User Manual - Electronic Kits
LOC3 Dual Laser Occupancy Detector
User Manual
Version 1.02
July 25, 2011
by
Mike Dodd
[email protected]
This manual and the LOC3 firmware programmed into the microprocessor are copyright © 2011 Michael M. Dodd
All rights reserved
Table of Contents
Introduction........................................................................................................................................................ 4
User manual road map..................................................................................................................................... 4
My LOC3 is a kit....................................................................................................................................... 4
My LOC3 is already assembled.............................................................................................................5
What is the SYC3?........................................................................................................................................ 6
Chapter 1 – Assembly...................................................................................................................................... 7
Getting started.............................................................................................................................................. 7
Identifying the components........................................................................................................................8
Parts list...................................................................................................................................................... 12
1Component Layout..................................................................................................................................14
Step-by-step assembly instructions.........................................................................................................15
Chapter 2 – Testing.........................................................................................................................................21
Choosing a power supply..........................................................................................................................21
Connecting the power supply...................................................................................................................21
Voltage checkout........................................................................................................................................ 21
Basic circuit checkout............................................................................................................................... 22
Microprocessor checkout..........................................................................................................................24
Laser and photocell checkout..................................................................................................................26
Chapter 3 – Planning for Installation...........................................................................................................29
Understanding yard throat occupancy detection...................................................................................29
Covering the throat.................................................................................................................................... 30
Chapter 4 – Installing and Wiring the Lasers and Photocells..................................................................33
What wire to use........................................................................................................................................ 33
Network cable........................................................................................................................................ 33
Telephone cable.................................................................................................................................... 33
Hookup wire........................................................................................................................................... 34
Wiring pin header connectors.............................................................................................................34
Laser and photocell wiring........................................................................................................................35
Detector output wiring...............................................................................................................................36
Isolated output....................................................................................................................................... 37
Direct output.......................................................................................................................................... 37
Testing the laser and photocell wiring...............................................................................................38
Laser mounting.......................................................................................................................................... 39
Photocell mounting....................................................................................................................................39
LOC3 Dual Laser Occupancy Detector User Manual
Page 2
Mirror mounting......................................................................................................................................... 40
Aiming the laser......................................................................................................................................... 40
Fine-tuning the aim...............................................................................................................................40
Aiming factors........................................................................................................................................ 41
Mirrors..................................................................................................................................................... 41
Finally...................................................................................................................................................... 41
Connecting the LOC3 to other equipment..............................................................................................42
Connecting the LOC3 to an SYC3........................................................................................................42
Connecting the LOC3 to generic equipment.....................................................................................42
Schematic Diagram........................................................................................................................................ 44
LOC3 Dual Laser Occupancy Detector User Manual
Page 3
INTRODUCTION
The LOC3 Dual Laser Occupancy Detector is an electronic circuit that flashes a laser beam across a
model railroad yard throat and signals when the throat is vacant or occupied. It offers these features:
✔ Monitors two separate yards.
✔ Powers two red lasers, and has two independent detection circuits.
✔ Adjustable photocell sensitivity reduces the effect of ambient room light.
✔ Programmable detection delay so gaps between cars moving through yard throat don't trigger
false “vacant” signals.
✔ Laser beam can cover even large yard throats by using mirrors to direct it.
✔ Interfaces directly to the SYC3 Staging Yard Controller for simple automated hidden staging yard
operation.
✔ Can interface to most other model railroad electronic devices requiring an “occupied/vacant”
signal.
✔ Operates from a single 12V DC power supply.
USER MANUAL ROAD MAP
Even though the LOC3 is a simple electronic device, integrating it into your model railroad requires
considerable thought and planning. Consequently, this user manual, at 44 pages, contains a lot of
important information and illustrations.
A significant portion of the manual covers assembling the LOC3 kit and checking it out. If you
purchased your LOC3 assembled and tested, you can skip these sections, and get started planning your
staging yard and installing the LOC3 on your railroad.
I recommend following this road map. Throughout this manual, “hot links” to other pages and even
Web sites are shown in blue (unless right next to the target location). Click the mouse pointer on one of
these links to go directly to that location . For example, clicking this link: Getting started takes you
directly to the Getting started section on page 7. You can use your PDF reader's Back button [] to
return to where you were.
My LOC3 is a kit
1. Begin with the Getting started section, especially the part about soldering and installing
electronic components on the PCB.
2. Refer to the table starting on page 8 to identify the components.
3. Inventory the parts that came with the kit, and check them against the list on page 12.
4. Look over the Component Layout to become familiar with the LOC3 circuit board.
5. Assemble the LOC3, following the instructions starting on page 15.
6. Choose a power supply and check out the LOC3, starting on page 21.
7. Check out the lasers and photocells on page 26.
8. Read Chapter 3 – Planning for Installation to plan your staging yard(s), and locations for the
lasers and photocells, and possibly mirrors.
9. In particular, read Understanding yard throat occupancy detection so you know how the
LOC3 works.
LOC3 Dual Laser Occupancy Detector User Manual
Page 4
10. Also read Covering the throat for tips on designing a yard throat that lends itself well to laser
occupancy detection.
11. Read Chapter 4 – Installing and Wiring the Lasers and Photocells to install these
components for reliable operation.
12. Read Wiring pin header connectors to learn how to attach wires to the metal contacts used in
the plastic connectors that plug onto the LOC3's pin headers.
13. Read Detector output wiring again to verify that the LOC3's detection output type is correct, and
to learn how to connect he LOC3 to your equipment (reading this the first time is part of the
assembly instructions).
14. Connect and test the LOC3 to the SYC3 or generic equipment needing occupancy signals. This
begins on page 42.
My LOC3 is already assembled
Your assembled LOC3 was tested with the included photocells (and lasers, if you ordered them at the
same time), and was fully operational when shipped. It needs only to be connected to a 12V DC power
supply, along with the lasers, photocells, and equipment needing occupancy signals.
You can skip the assembly and testing steps above, but you still should read about how the LOC3
works, and how to integrate it into your railroad.
But first, read Detector output wiring to confirm that the LOC3 output type is correct for your
equipment. The LOC3 was assembled for “direct” or “isolated” outputs according to information you
provided when you placed the order.
I recommend these pieces of the user manual:
1. Read about Choosing a power supply and connecting it, on page 21
2. Read Chapter 3 – Planning for Installation to plan your staging yard(s), and locations for the
lasers and photocells, and possibly mirrors.
3. In particular, read Understanding yard throat occupancy detection so you know how the
LOC3 works.
4. Also read Covering the throat for tips on designing a yard throat that lends itself well to laser
occupancy detection.
5. Read Chapter 4 – Installing and Wiring the Lasers and Photocells to install these
components for reliable operation.
6. Read Wiring pin header connectors to learn how to attach wires to the metal contacts used in
the plastic connectors that plug onto the LOC3's pin headers.
7. Connect and test the LOC3 to the SYC3 or generic equipment needing occupancy signals. This
begins on page 42.
LOC3 Dual Laser Occupancy Detector User Manual
Page 5
What is the SYC3?
This manual sometimes mentions that the LOC3 can be used with the SYC3 Staging Yard
Controller. What is the SYC3?
The SYC3 is an electronic device that solves the hassle of running trains into and out of hidden
staging yards where the trains can't be seen. It does three things:

Aligns the turnouts to the correct track, so train crews don't have to throw multiple toggle
switches. The train crew selects the track with a single switch, then presses a button. The
SYC3 does the rest.

Turns on track power to the designated track only when a train is supposed to be moving on
it. When the train clears the yard throat, the SYC3 turns off power to that track.
• This feature prevents a careless crew from running an inbound train into the end of the
staging track.
• Having unpowered staging tracks also prevents DCC-equipped engines and lighted cars
from “cooking” while sitting in the staging yard.

Monitors the train's progress through the yard throat, and signals the crew.
• Knowing when an inbound train is completely in the yard and stopped on an unpowered
track tells the crew that it's okay to shut off the throttle – the trip is over.
• For outbound crews, the throat-occupied signal is a comforting indication that the train is
actually moving out of the yard.
The LOC3 works seamlessly with the SYC3, but it also can connect to other equipment needing
“occupied” and “vacant” indications for yard throats – it is not limited to the SYC3.
SYC3 details and ordering information can be found at http://electronics.mdodd.com/syc3.html
LOC3 Dual Laser Occupancy Detector User Manual
Page 6
CHAPTER 1 – ASSEMBLY
Getting started
You need to know how to solder electronic circuits to assemble the LOC3 kit. If you are unfamiliar
with soldering techniques, you can find a good tutorial on the Web, such as this one at
http://www.aaroncake.net/electronics/solder.htm
You also can purchase a solder practice kit, such as this one:
http://www.makershed.com/ProductDetails.asp?ProductCode=MKEL2 It is wise to be confident of your
your soldering skills before assembling the LOC3.
Soldering electronic components requires the use of a low-wattage soldering iron, about 35 to 45
watts. Ideally, use a temperature-controlled soldering station such as the Weller WTCPT that maintains a
tip temperature of 700° to 800°. The WTCPT is available from many electronics distributors, including
HMC Electronics: http://www.hmcelectronics.com/cgi-bin/scripts/product/1980-0217/?
gclid=CPaA2vaMuZ4CFchn5QodJ2l0pg
Use only rosin-core solder on electronic circuits. Never use acid-core solder, and never use flux of
any kind.
Remember: Rosin-core solder only and no flux. You can buy rosin-core solder at Radio Shack
(#64-009 (http://www.radioshack.com/product/index.jsp?productId=2062715) or other electronics
suppliers, such as Digi-Key (http://www.digikey.com/) or Mouser (http://www.mouser.com/).
The LOC3 is built on a high-quality printed circuit board (PCB) with plated-through holes. Platedthrough holes have metal walls, so the solder readily flows into the hole and out onto the soldering pad
on the opposite side of the PCB.
This means you can solder components such as resistors and diodes from the front side of the PCB,
and the molten solder will flow through to the back side. This eases assembly because you can press the
component firmly against the PCB while soldering (if soldering from the back side, it's possible that the
component could drop away from the PCB).
Trim long component leads close to the back of the PCB after soldering. This applies to resistors,
capacitors, LEDs, and diodes, not to IC sockets, pin headers, or terminal blocks.
Resistors and diodes used on the LOC3 PCB have 0.4” hole spacing. It is helpful to buy or make a
lead-bending jig to avoid measuring each time such a component must be installed. This photo shows a
commercial jig holding a resistor with its leads bent downward 90° at the correct 0.4” spacing. A similar
jig could be easily fabricated from styrene.
Figure 1: Lead-bending jig.
LOC3 Dual Laser Occupancy Detector User Manual
Page 7
Identifying the components
This table describes the parts you'll find in the LOC3 kit, and includes photos to help you identify
them. If an item is noted as “polarized,” pay extra attention to its orientation when you insert it into the
PCB, and be sure to orient it exactly as directed.
Component
Integrated circuit (“IC”
or “chip”)
Description
Rectangular package
with two rows of legs.
Photo
Notes
ICs can be destroyed by
static electricity, so keep
them in their black
conductive foam until
ready to insert them into
the sockets on the PCB.
Before handling one,
touch your hand to a
metal object to discharge
any static electricity.
ICs are polarized, and
must be inserted into
their sockets with the
end-notch oriented as
shown on the
component layout
printed on the PCB and
shown on page 14.
Voltage regulator or
transistor
Black, semi-circular
device with three leads
on the bottom. Labeled
LM317, 2N3904, or
78L05.
Polarized. Install with the
flat side as shown on the
component layout
printed on the PCB and
shown on page 14.
Resistor
Small cylinder with
colored bands that
identify the resistor's
value.
The assembly
instructions state the
color code for each
resistor when it is
installed.
Important! This kit
contains resistors having
values of 470Ω, 4.7K,
and 47K. The only
difference in these
resistors is the color of
the third band from the
left. The first two bands
of these resistors are
yellow and violet. If the
third band is brown, the
resistor's value is 470Ω.
If red, the value is 4.7K.
If orange, the value is
LOC3 Dual Laser Occupancy Detector User Manual
To read the color code,
place the gold band to
the right, then read the
other bands from left-toright. This 470Ω
resistor's color code is
yellow-violet-brown.
Ignore the gold band.
Use care identifying the
colored bands; installing
the wrong resistor will
result in improper
Page 8
47K. Refer to the photo
to the right to identify
this band. The resistor in
the photo has a brown
third band, so has a
value of 470Ω.
operation or no
operation at all. If in
doubt about a resistor's
value, measure it with a
multimeter.
An electrolytic capacitor
is a black cylinder and
has its value and other
symbols printed on its
case.
Electrolytic capacitors
are polarized.
Capacitor
A ceramic capacitor has
two leads on one edge,
and is marked with
numbers to indicate its
value.
Electrolytic capacitor
Ceramic capacitor
Ceramic capacitors are
not polarized.
Diode
Black cylinder with a
band on one end.
Polarized. Install with the
banded end as shown
on the component layout
printed on the PCB and
shown on page 14.
LED
Red or yellow cylinder
with two pins on one
end. The cylinder has a
flat side at the base, and
one lead is slightly
longer than the other.
LEDs are polarized.
LOC3 Dual Laser Occupancy Detector User Manual
Important! Sometimes
the an LED's flat side
may be very difficult to
identify, or might not
match the orientation
printed on the PCB.
Please ignore the flat
side, and install LEDs
with the long lead in
the hole with the
square solder pad.
Page 9
Photocell
Clear cylinder two pins
on one end. The cylinder
has a flat side at the
base, and one lead is
slightly longer than the
other.
Polarized. This
component is installed in
your yard throat, not on
the PCB. Wire it
according to the
instructions. on page 35.
Laser module
Metal cylinder with two
(purchased separately) wires connected to one
end, and an opening on
Laser modules may be
the opposite end.
purchased from me,
from online electronics
Danger! Never look
dealers, or salvaged
directly at an operating
from inexpensive laser
laser or point one at
pointers.
someone’s face. The
laser is bright enough to
The LOC3 requires one
permanently damage
laser for each yard
eyes. It is okay to look at
throat being monitored
the spot projected on a
(i.e., two lasers for two
wall or other object.
yards).
Polarized. This
component is installed in
your yard throat, not on
the PCB. Wire it
according to the
instructions starting on
page 35.
Pin header
Black plastic strip with
square metal pins.
Provides connections to
external components
using header connectors
with metal contacts (next
item).
Solder the short pins into
the PCB
Header connector and
contacts
White plastic block with
square holes that accept
metal contacts. Mates
with a pin header.
Used to connect the
laser, photocell, and
other equipment to the
LOC3. This plugs onto
the pin header shown
above.
Header
connector
contacts
Terminal block
Rectangular plastic block
with holes along one
side, screws along the
top, and pins on the
bottom.
LOC3 Dual Laser Occupancy Detector User Manual
Contacts must be
attached to wires and
inserted into the square
holes in the plastic
housing. See page 34
for details.
Install with the side holes
facing outward from the
PCB.
Page 10
Note: The terminal block
might have the wire
holes on top and the
screws on the side, such
as this one. Install this
style with the screws
facing outward from the
PCB.
DIP switch
Black plastic block with
multiple slide switches
on the top and pins on
the bottom.
LOC3 Dual Laser Occupancy Detector User Manual
Polarized. Install with the
switch numbers as
shown on the
component layout on
page 14 and printed on
the PCB.
Page 11
Parts list
The LOC3 kit contains these parts. Please check the kit contents against this list to verify that all
components are present. Items with a light yellow background are not mounted on the PCB, but instead
are installed on your layout or used to connect other equipment. Note that laser modules must be
purchased separately.
Refer to the table starting on page 8 for details about identifying the components.
Quantity
Description
Identifying Marks
Designation
1
Printed circuit board
1
47ųF Electrolytic capacitor
47ųF
C1
3
0.1ųF Disk capacitor
104
C2, C3, C4
4
1N4001 diode
1N4001
D1, D2, D3, D4
1
2-position screw terminal
block
PCB
J1
Note: The following three pin headers must be cut from the single long header provided.
2
2-position pin header
Black strip with pins
J2, J4
2
3-position pin header
Black strip with pins
J3, J5
1
dual 4-position pin header
Black strip with pins (cut two 4-position
headers)
JB1
1
2-position jumper block for
JB1
Black plastic block with 2 holes and
metal contacts inside
2
Yellow LED
LED1, LED3
2
Red LED
LED2, LED4
1
2N3904 transistor
2N3904
Q1
1
220Ω resistor
Color code: red-red-brown
R16
7
470Ω resistor
Color code: yellow-violet-brown
R4, R5, R7, R11,
R12, R13, R15
3
4.7K resistor
Color code: yellow-violet-red
R1, R8, R17
4
47K resistor
Color code: yellow-violet-orange
R2, R6, R9, R14
2
20K potentiometer
203
R3, R10
1
PIC16F267 customprogrammed microprocessor
16F627
U1
1
78L05 5V regulator
78L05
U2
1
LM317 voltage regulator
LM317
U3
1
LM324 op amp
LM324 or 324
U4
2
4N29 optical isolator
6-pin DIP chip
U5, U6
1
28-pin DIP socket for U1
X1
1
14-pin DIP socket for U4
X4
2
6-pin DIP sockets for U5, U6
X5, X6
LOC3 Dual Laser Occupancy Detector User Manual
Page 12
2
2-position pin header socket
connector for J2, J4, plus
contacts
White plastic block with holes; metal
contacts are separate
2
3-position pin header socket
connector for J3, J5, plus
contacts
White plastic block with holes; metal
contacts are separate
2
Photocell
Clear plastic cylinder with 2 wire leads
Quantity
ordered
Laser module
Brass cylinder with 2 wires
LOC3 Dual Laser Occupancy Detector User Manual
Laser (optional;
purchase
separately)
Page 13
1 Component Layout
Refer to this component layout while assembling the LOC3. The “front” side of the PCB is shown
here; the reverse side is referred to as the “back” side in the assembly instructions on the following
pages.
Figure 2: LOC3 component layout.
LOC3 Dual Laser Occupancy Detector User Manual
Page 14
Step-by-step assembly instructions
Print this page and the next one so you can check off each step as you complete it. Then you'll have
a record in case you are interrupted.
The strategy is to install the low-profile components (resistors, diodes) first,then progressing to taller
components. This provides the best access for soldering on the front side of the PCB.
Follow the step-by-step Instructions in order, and solder only when the instructions say to do so.
 Install three resistors R1, R8, and R17 (4.7K ohms, color code: yellow-violet-red). Bend the
leads at 0.4” spacing, insert into the holes, and solder. Oops! The PCB component layout
erroneously shows a 10K value for R1 and R8. The correct value is 4.7K, as stated here.
 Install four resistors R2, R6, R9, and R14 (47K ohms, color code: yellow-violet-orange). Bend
the leads at 0.4” spacing, insert into the holes, and solder and trim the leads. Cut off the excess
leads on the back side of the PCB.
 Install seven resistors R4, R5, R7, R11, R12, R13, and R15 (470 ohms, color code: yellow-violetbrown). Bend the leads at 0.4” spacing, insert into the holes, solder, and trim the leads. Cut off
the excess leads on the back side of the PCB.
 Install one resistor R16 (220 ohms, color code: red-red-brown). Bend the leads at 0.4” spacing,
insert into the holes, solder, and trim the leads. Cut off the excess leads on the back side of the
PCB.
 Install four diodes D1, D2. D3. and D4. Bend the leads at 0.4” spacing and insert into the holes.
Diodes are polarized – double-check the orientation before soldering. Solder as quickly as
possible to avoid heat damage, then trim the leads. Cut off the excess leads on the back side of
the PCB.
Your PCB should look like this after installing diodes D1 – D4.
Figure 3: PCB with low-profile components.
LOC3 Dual Laser Occupancy Detector User Manual
Page 15
 Install X1, the 18-pin socket for U1 and X4, the 14-pin socket for U4. Be sure the end notch
matches the notch on the PCB and component layout. Insert all the pins into the holes, then bend
opposite-corner pins slightly on the back side of the PCB to hold the socket in place. Press each
socket tightly against the PCB, and solder all pins on the back side. Double-check to ensure that
all pins are soldered – a pin that's not soldered will prevent correct operation.
STOP! Before installing X5 and X6, the 6-pin sockets for U5 and U6, read Detector output
wiring on page 36. You must know what type of input circuit is present on the equipment using the
LOC3's detection outputs so you can choose “isolated” or “direct” outputs for the LOC3.
Note in this table the type of LOC3 output needed for each piece of equipment. You will need this
information in the next few steps, when inserting the chips into the sockets, and when connecting
your other equipment to the LOC3.
Connector
Town Name
Equipment
LOC3 Output Type
J2
 Isolated – Install X5
 Direct – Omit X5
J4
 Isolated – Install X6
 Direct – Omit X6
Table 1: LOC3 output types
 Refer to Table 1 above. If the J2 output type is “isolated,” install X5, the 6-pin socket for U5. Be
sure the end notch matches the notch on the PCB and component layout. Insert all the pins into
the holes, then bend opposite-corner pins slightly on the back side of the PCB to hold the socket
in place. Press each socket tightly against the PCB, and solder all pins on the back side. Doublecheck to ensure that all pins are soldered.
 Refer to Table 1 above. If the J4 output type is “isolated,” install X6, the 6-pin socket for U6, as in
the preceding step. Solder all pins on the back side.
Your PCB should look like this after installing the jumpers for the “isolated” detector output. Note
the sockets for U5 and U6.
LOC3 Dual Laser Occupancy Detector User Manual
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Figure 4: PCB with U5/U6 “isolated” sockets.
 Refer to Table 1 above. If the J2 output type is “direct,” use component lead cutoffs to install
jumper wires in the U5 location: Pin 1 to pin 5; pin 2 to pin 4. Follow the red lines in Figure 5,
below. Insert the bare wires into the designated holes, then solder. Cut off the excess leads on
the back side of the PCB.
 Refer to Table 1 above. If the J4 output type is “direct,” use component lead cutoffs to install
jumper wires in the U6 location: Pin 1 (square pad) to pin 5 (middle of opposite row); pin 2 to pin
4. Follow the red lines in Figure 5. Insert the bare wires into the designated holes, then solder.
Cut off the excess leads on the back side of the PCB.
Figure 5: U5 and U6 jumpers for direct outputs.
The PCB should look like this after installing the jumpers for the “direct” detector output. Note the
wire jumpers in the U5 and U6 positions.
LOC3 Dual Laser Occupancy Detector User Manual
Page 17
Figure 6: PCB with U5/U6 “direct” jumpers
 Install two potentiometers R3 and R10. Polarized – insert the three leads into the holes, then
solder and trim the leads. Note: Unfortunately, the PCB layout places LED1 and LED2 in front of
R3, and U4 (in its socket) in front of R10. These components prevent easy access to the
adjusting slot with a screwdriver.
To provide easier access, consider tilting R3 and R10 backward about 25º when installing them.
Simply rest the rear of the potentiometer on the PCB and solder those two leads. Then tilt it back
and solder the single front lead. This photo shows the tilted potentiometers; the better access is
readily apparent. You also can bend LED1 and LED2 slightly toward the PCB edge if more
clearance is needed for R3.
Figure 7: R3 and R10 tilted backward.
 Install capacitor C1 (47μF, round, black). Polarized – double-check the orientation before
soldering. Match the “+” sign on the capacitor with the “+” sign on the component layout. The
LOC3 Dual Laser Occupancy Detector User Manual
Page 18
capacitor's long lead goes into the hole with the square solder pad. Hold the capacitor against the
PCB, bend the leads slightly on the back side to hold it in place, then solder on the back side. Cut
off the excess leads on the back side of the PCB.
 Install three capacitors C2, C3, and C4 (0.1μF, dark red, marked 104). Solder, then cut off the
excess leads on the back side of the PCB.
Note: The following three steps install a transistor and two voltage regulators in packages with
three leads on the bottom. The PCB holes are spaces wider than the component lead spacing so
that if you spread the leads slightly to fit the holes, then press the component toward the PCB, the
splayed leads will hold it in place as you solder. Leave the component standing about ¼” above
the PCB. If you press it closer, the leads could break off.
I recommend inserting all three components before soldering. Then solder one lead on each
component in turn, come back and solder the second lead, and finally the third. This allows time
for each component to cool before the next lead is soldered, lessening the chance of heat
damage than if all three leads are soldered at once.
 Install U2, the 78L05 voltage regulator.
Error! The PCB is incorrect for U2 – it must be installed rotated 180º from the component layout.
Orient the component so the flat side is opposite to that shown on the PCB diagram, insert the
three leads into the holes, leaving the component about ¼” above the PCB, then solder the three
leads. This photo shows the correct orientation for U2. The orientation diagrams are correct for
U3 and Q1, installed in the next two steps. Trim the leads on the back of the PCB.
Pay attention to this! If the PCB is powered-up with U2 installed incorrectly, U2 will be
destroyed. See page 22 in the Checkout section.
Figure 8: Correct orientation for U2.
 Install U3, the LM317 voltage regulator. Orient the component so the flat side matches the
diagram on the PCB, insert the three leads into the holes, leaving the component about ¼” above
the PCB, then solder the three leads. Cut off the excess leads on the back side of the PCB.
 Install Q1, the 2N3904 transistor. Orient the component so the flat side matches the diagram on
the PCB, insert the three leads into the holes, leaving the component about ¼” above the PCB,
then solder the three leads. Cut off the excess leads on the back side of the PCB.
 Install J1, the 2-screw connector block. Hold it firmly against the PCB, and solder on the back
side, and trim the leads.
 Using wire cutters, snip two 2-pin sections from the long pin header strip, and install J2 and J4,
the 2-pin headers. Insert the short pins into the holes and solder on the back side of the PCB.
 Snip two 3-pin sections from the long pin header strip, and install J3, and J5, the 3-pin headers.
Insert the short pins into the holes and solder on the back side of the PCB.
 Snip two 4-pin sections from the long pin header strip, and insert these into the two rows of four
holes at JB1, the Detector Delay Seconds location. Insert the short pins into the holes and solder
LOC3 Dual Laser Occupancy Detector User Manual
Page 19
on the back of the PCB, then trim the leads.
 Install yellow LED1 and LED3. LEDs are polarized – double-check the orientation, then solder on
the back side of the PCB. Please see the note on page 9 about the LED flat side. Ignore the flat
side and insert the long lead into the hole with the square solder pad. Solder as quickly as
possible to avoid heat damage. Cut off the excess leads on the back side of the PCB.
 Install red LED2 and LED4. Polarized – double-check the orientation, as above. Ignore the flat
side and insert the long lead into the hole with the square solder pad, then solder as quickly as
possible on the back of the PCB. Cut off the excess leads on the back side of the PCB.
This completes assembly of the LOC3. Your PCB should look like Figure 29 below. When you're sure
everything is right, continue to page 21 to check-out the system.
Figure 9: PCB assembly complete.
LOC3 Dual Laser Occupancy Detector User Manual
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CHAPTER 2 – TESTING
Choosing a power supply
The LOC3 requires a DC power source that produces12V ±1.5V. A good choice for this is a
“switching” power supply such as those used to charge laptop computer batteries. Switching power
supplies produce “clean” (low-noise) regulated voltage that is ideal for electronic circuits. Switching
power supplies can be purchased inexpensively from All Electronics (http://allelectronics.com/).
The LOC3 draws, on average, about 23 milliamps (0.023A) with both lasers off, increasing to about
80 milliamps (0.08A when both lasers are on (the “on” current varies with the lasers used). A typical
switching power supply is this one: http://www.allelectronics.com/make-a-store/item/PS-12170/12-VDC1.7-AMP-SWITCHING-SUPPLY/1.html which produces 12V at 1.7 amps, which is far more than
sufficient. (Note: This model might not always be available. All Electronics sells industry surplus, and
when an item sells-out, it's gone. If this is the case, simply look for a similar item.)
Do not use an unregulated “power adapter” commonly sold for use with inexpensive electronic
equipment such as portable radios. These are notorious for producing voltages nowhere close to
their stated output. For example, a “12V” power adapter might actually produce a voltage as low as
8V or as high as 16V, and it might vary with the load. Since the LOC3 flashes two lasers on and off,
its current draw fluctuates, so it needs a power supply that produces a stable voltage. Your best
choice is a switching power supply.
Rather than dedicating a single power supply to the LOC3, you might want to run a power bus
around your layout. Run one wire for +12V and another wire for common. You can tap into this
power bus everywhere you need +12V for electronic devices, lights, or stall-motor switch machines.
A second power supply and a third wire gives you -12V as well, which allows controlling stall-motor
switch machines with SPDT switches instead of larger and more-expensive DPDT switches.
If you decide to do this, choose power supplies capable of supplying the maximum current you'll
need. A 1.7-amp supply will power several electronic devices plus at least 50 stall-motor switch
machines. Larger supplies are readily available at All Electronics. This one:
http://www.allelectronics.com/make-a-store/item/PS-1235/12VDC-3.5A-SWITCHING-POWERSUPPLY/1.html produces 12V at 3.5A and costs $12.50 (again, this item might not always be
available).
Connecting the power supply
Check with a voltmeter to be sure you know which power supply wire is positive and which is
negative. Connect the positive power supply wire to the “+12V” screw terminal on J1 and the negative
wire to the Com screw terminal on J1. Do not turn on the power at this time.
Voltage checkout
At this point, your PCB should have all soldered components installed, empty U1 and U4 sockets
(and empty U5 and U6 sockets if using isolated outputs), and the power supply wired to J1.
LOC3 Dual Laser Occupancy Detector User Manual
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You will need a multimeter capable of reading DC voltage to 15V. Connect the negative multimeter
lead to the Com pin on J3 or J5, and keep it there for all of the checkout tests.
You also will need a “test lead” that can clip onto or touch connector header pins, component leads,
and integrated circuit pins. This can be as simple as a length of wire with bare ends or a wire with a
spring-loaded clip (e.g., E-Z Hook) or “alligator clip” on each end.
Refer to the component layout on page 14 to identify the location of the points to touch the positive
multimeter lead or the test lead in the following steps. Orient your PCB so it matches the component
layout orientation. When the instructions mention the “top edge” of the PCB, this is the edge at the top of
the component layout.
 Connect the positive multimeter lead to the PCell pin of J3 or J5.
 Turn on the power supply. The multimeter should read 5V. If it does not, turn off the power. If the
reading is close to the power supply voltage, it is likely that U2 is installed backwards, and has
been destroyed (remember the orientation diagram error caution on page 19).
If U2 is destroyed, email me for a free replacement.
If the multimeter reads no voltage at all, it is likely that one or more of diodes D1, D2, and D3 are
installed backward. This damages nothing, but prevents the LOC3 from operating. Unsolder the
backward diode and install it correctly.
 Connect the positive multimeter lead to the Laser pin of J3 or J5.
 Turn on the power supply. The multimeter should read approximately 3.5V. If it does not, turn off
the power. If the reading is close to the power supply voltage, it is likely that U3 is installed
backwards, and has been destroyed.
If U3 is destroyed, replace it with a new LM317 from Digi-Key (http://www.digikey.com) or Mouser
Electronics (http://www.mouser.com).
 With the power supply on and the multimeter reading about 3.5V, clip one end of your test lead to
the Pcell pin of J3 or J5.
 Locate R17, near JB1, the Detector Delay Seconds jumper block. Touch the free end of your test
lead to R17's lead closest to the PCB top edge (arrow in xxx. The multimeter reading should drop
to about 1V. If it does, not, Q1 is likely defective. Replace it with a new 2N3904 from Digi-Key
(http://www.digikey.com) or Mouser Electronics (http://www.mouser.com).

Figure 10: R17 test point.
At this point, the LOC3's power supply section is working, and so is the laser power circuit.
Basic circuit checkout
With the power supply working, we can move on to checking the components that monitor the
photocell and signal “occupied” or “vacant.”
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 Insert the LM324 14-pin chip into the socket at U4. If the LM324's two rows of pins are splayed
outward, carefully bend them inward slightly by laying the component sideways on a flat surface
and pressing gently. The pins should line up with the socket contacts. Be absolutely certain that
the notch or dimple in one end of U4 matches the notch in the end of the socket. The socket
notch is adjacent to the red LED4, as shown in this photo.

Figure 11: U4 LM324 orientation.
 Connect one end of your test lead to the Com pin on J3 or J5. You may disconnect the
multimeter's negative lead, or just use the free Com pin on the other header.
 Turn on the power. All four LEDs should light up. If yellow LED1 is off, adjust R2 until it lights. If
yellow LED3 is off, adjust R10 until it lights. If the red LEDs are off, don't worry about them now.
 Touch the free end of your test lead to the PCell (center) pin of J3. Yellow LED1 should turn off
each time the pin is touched. If not, check that the other end is actually connected to the Com pin.
Also check that U4 is inserted into its socket correctly, and that all pins are in their socket
contacts, not bent under or outward.
If U4 is inserted backward, turn off power , then remove it and insert it correctly. Turn on power
and try the test again. If the yellow LED still doesn't turn on, U4 is probably destroyed. Replace it
with a new LM324 from Radio Shack, Digi-Key (http://www.digikey.com) or Mouser Electronics
(http://www.mouser.com).
 Touch the free end of your test lead to the PCell (center) pin of J5. Yellow LED3 should turn off
each time the pin is touched. If not, check and correct the U4 items listed above.
With both yellow LEDs working, we can move on to the red LEDs. Do not proceed until the yellow
LEDs work, because U4 also controls the red LEDs.
 Leave 24one end of your test lead connected to the Com pin on J3 or J5.
 Touch the free end of your test lead to pin 1 of the empty socket for U1 (see Figure 12 below to
identify this pin). Red LED2 should turn off each time the pin is touched. If not, check and correct
the U4 items listed above. If LED2 is off when not touching the pin, skip this step – the “floating”
input to U4 is likely switching to the opposite state, producing a useless indication. This condition
will be corrected when U1 is installed in its socket.
LOC3 Dual Laser Occupancy Detector User Manual
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Figure 12: U1, pins 1 and 3.
 Touch the free end of your test lead to pin 3 of the empty socket for U1 (see Figure 12 above to
identify this pin). Red LED4 should turn off each time the pin is touched. If not, check and correct
the U4 items listed above. If LED4 is off when not touching the pin, skip this step, as described in
the previous step.
 Turn off the power.
At this point, the circuit that connects the LOC3's microprocessor to your layout is functional.
Microprocessor checkout
With the power supply and interface circuitry working, we can move on to checking the
microprocessor, and verify that the LOC3 operates the lasers and monitors the photocells.
 Install the small black shunt block on two pins of JB1 to set the detection delay; one or two
seconds is a good choice for now. Refer to this photo for details.
Figure 13: JB1 shunt for 2 seconds.
 Insert the PIC16F527 18-pin chip into the socket at U1. Caution! Static electricity can destroy
this chip. Keep it in its anti-static black foam until inserting it into the socket, and touch
something metallic to discharge static from your body before touching the chip. The pins
should line up with the socket contacts because the chip was inserted into a socket for testing
LOC3 Dual Laser Occupancy Detector User Manual
Page 24
before shipment, so there should be no need to straighten. Be absolutely certain that the notch or
dimple in one end of U1 matches the notch in the end of the socket. The socket notch is adjacent
to JB1, as shown in this photo. The paint dot identifies the chip as programmed for the LOC3.
Figure 14: U4 PIC 16F627 orientation.
 Turn on the power and watch the two red LEDs. Both LEDs should flash five times, then remain
lighted on the sixth flash. If they do not flash, turn off the power. Check the orientation of U1 and
reverse it if it was installed backwards, then turn on the power again and watch for the flashing
red LEDs. If they still do not flash, U1 probably was destroyed by the incorrect orientation, or by
static electricity while handling it. Email me to buy a replacement.
If the red LEDs flash, the microprocessor is working, and the LOC3 is almost ready to put into
service.
 Connect one end of your test lead to the PCell pin on J3. Touch and hold the free end to the Com
pin on J3. The yellow LED1 should turn off. After the number of seconds set on JB1, the red
LED2 should turn off.
 Remove the test lead from the Com pin on J3. The yellow LED1 and red LED2 should both turn
on immediately.
 Repeat the previous two steps for J5, watching yellow LED3 and red LED4. For each pin header,
J3 or J5, the corresponding yellow LED should turn off when you touch the test lead to Com, and
one to five seconds later (set by the JB1 shunt), the corresponding red LED should turn off. When
you break the connection to Com, the corresponding yellow and red LEDs should turn on.
LOC3 Dual Laser Occupancy Detector User Manual
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What does this test mean?
Connecting the PCell pin to the Com pin is exactly what the photocell does when light falls on it.
Light striking the photocell means the yard throat is vacant (no obstructions). Each time this occurs,
the microprocessor, U1, begins timing. If the connection remains unbroken for the number of
seconds set by the JB1 shunt, U1 decides that the throat really is vacant, and turns on the red LED
(and also activates the detector output signal on J2 or J4).
If, however, the connection is broken, even for an instant, U1 concludes that an obstruction is
blocking the light, stops timing, does not turn on the red LED, and waits for the next PCell–Com
connection (“vacant”).
A train moving through the yard throat will break the beam, causing the photocell to open the
PCell–Com connection (“occupied”). But if the laser beam passes between coupled cars, the JB1
delay prevents U1 from immediately signaling “Vacant,” which would be false.
You can demonstrate this by jiggling the test lead connection. The jiggles represent gaps
between cars, and the yellow LED should flash with each jiggle. But the red LED won't turn on until
the connection is stable for the required number of seconds.
The fact that the red LED turns on nearly simultaneously with the yellow LED proves that the
LOC3 signals “occupied” immediately – the delay applies only to the “vacant” signal.
Laser and photocell checkout
In this section, we will connect a laser and photocell to each of the two LOC3 inputs, and verify that
each works separately and together. To do this, you will need to connect these components to J3 and J5,
where you connected your test lead in the previous steps.
Here, you must make a choice. If you have test leads that can attach to the three pins of J3 or J5
simultaneously, you can connect the laser and photocell using them (you will need four test leads). An
alternative is to wire the laser and photocell to the connectors you'll use when installing the system on
the layout. However, this requires final-length cables, so you'll need to know where the laser, photocell,
and LOC3 will be located, and cut the cables accordingly. So you should read Chapter 3 – Planning for
Installation and Chapter 4 – Installing and Wiring the Lasers and Photocells to determine these.
I recommend using test leads with spring-clip tips that will fit on the small header pins. If you choose
to make up final cables, please read the Wiring pin header connectors section starting on page 34.
Let's go for it. When the instructions say to “connect” a laser or photocell wire, they mean to do it with
a test lead or a metal contact in a 3-pin header connector, and soldering the distant end of the wire to the
laser or photocell wire.
 Turn off the power.
 Connect the short lead of a photocell to the PCell pin of J3.
 Connect the long lead of the same photocell to the Com pin of J3.
 Turn on the power. All four LEDs should light up.
 Shine a bright light (e.g., a flashlight) into the end of the photocell. Yellow LED1 should turn off
while the light is striking the photocell. If not, adjust R3 until it does.
 Remove the light from the photocell, and LED1 should turn on.
 Turn off the power.
 Connect the short lead of a photocell to the PCell pin of J5.
LOC3 Dual Laser Occupancy Detector User Manual
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 Connect the long lead of the same photocell to the Com pin of J5.
 Turn on the power. All four LEDs should light up.
 Shine a bright light into the end of the photocell. Yellow LED3 should turn off while the light is
striking the photocell. If not, adjust R10 until it does.
 Remove the light from the photocell, and LED3 should turn on.
 Turn off the power. Leave the photocell connected to J5.
Warning! Danger!
You will connect and test the laser in the next steps.
Never look directly at an operating laser or point one at a person's or animal's face. The laser
is bright enough to permanently damage eyes.
It is okay to look at the spot projected on a wall or other object, but do not look into the open end
of an operating laser. Point the laser in a safe direction where there are no mirrors, and secure it
(tape it) to your workspace so there is no chance that anyone could look into it or that it could move
and point toward another person or a pet.
One laser sign humorously (and accurately) warns, “Do not look at laser with remaining eye!”
(http://www.ariven.com/store/ariven/warninglaser)
 Connect the red lead of a laser to the Laser pin of J5.
 Connect the black lead of the same Com to the PCell pin of J5, along with the long lead of the
photocell.
 Turn on the power. All four LEDs should turn on and the laser should begin flashing.
 Point the laser into the end of the photocell and hold it steady. Yellow LED3 should blink off each
time the laser flashes. This will be a very short blink, and might be hard to see. After the laser has
been aimed at the photocell for the number of seconds set by the JB1 shunt, red LED4 should
turn off. Remove the laser from the photocell, and LED4 should turn on.
 Turn off the power. Next, we will repeat the test for the other channel.
 Connect the short lead of a photocell to the PCell pin of J3.
 Connect the long lead of the same photocell to the Com pin of J3.
 Connect the red lead of a laser to the Laser pin of J3.
 Connect the black lead of the same Com to the PCell pin of J3, along with the long lead of the
photocell.
 Turn on the power. All four LEDs should turn on and the laser should begin flashing.
 Point the laser into the end of the photocell and hold it steady. Yellow LED1 should blink off each
time the laser flashes (again, this is quick, and might be hard to see). After the laser has been
aimed at the photocell for the number of seconds set by the JB1 shunt, red LED2 should turn off.
Remove the laser from the photocell, and LED2 should turn on.
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 Move the JB1 shunt to various delay times, and repeat the previous step for each delay. Measure
or estimate the number of seconds that pass between striking the photocell with the laser and
when LED2 turns on. This delay should correspond to the shunt position on JB1, as labeled on
the PCB. If the shunt is removed entirely, the delay is five seconds. To prevent loss of the shunt,
press it on any one pin of JB1 if you want the five-second delay.
Congratulations! Your LOC3 is fully functional, and ready for installation on your layout.
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CHAPTER 3 – PLANNING FOR INSTALLATION
This chapter discusses how to plan for laser detection of trains moving through yard throats –
typically in hidden staging yards.
Running trains into and out of a hidden staging yard can be nerve-wracking because crews can't see
their trains. The LOC3 was designed specifically to work with the SYC3 Staging Yard Controller, although
it can be used with other equipment for other purposes as well. The SYC3 needs to know when a train
enters and exits the yard throat, so it can signal the crew and also turn off power to the selected yard
track when the movement is complete.
The laser and photocell locations must be carefully planned, and often mirrors must be installed so
the laser beam covers the entire yard throat. The laser must sit high enough so the beam doesn't shoot
under car frames, but at the same time doesn't pass over flat cars.
Train speed through the yard throat also is a factor. Gaps between cars in a slow-moving train can be
detected as a vacant yard throat. The LOC3 allows you to set time delays from 1 to 5 seconds to
minimize false “vacant” detections.
Laser and photocell installation involves these steps:

Draw your yard throat layout and determine the best laser beam path and locations for the laser,
photocell, and mirrors. Refer to the illustrations and discussion starting on page 30 for ideas.

Measure the height of flat car bodies, so you can install the laser, photocell, and mirrors at this
height.

Install the laser, photocell, and possibly mirrors according to your diagram, and at the correct
height.

Set the LOC3 “vacant” detection delay according train speed through the yard throat.

Aim the laser and test for proper operation, using the LOC3's onboard LEDs.

Connect the LOC3's detection output to other equipment (e.g., SYC3) as needed.

Test the complete system for proper operation.
Understanding yard throat occupancy detection
The LOC3 detects train occupancy in a yard throat, not individual yard tracks. A laser beam is aimed
at a photocell. The beam covers the entire throat, and when it falls on the photocell, the throat is vacant.
When a train or any object breaks the beam, the throat is occupied, regardless of where in the throat that
object is located.
The LOC3 was designed for use in hidden staging yards, and interfaces directly to the SYC3 Staging
Yard Controller, which signals train progress and also shuts off power to the selected track when a train
clears the throat. The SYC3 is not required – the LOC3 can easily interface to other equipment.
With a hidden staging yard, operators need to know when their outbound train has entered the throat
(“Is my train running?”) and when their inbound train has cleared the throat so they can safely stop it
without fouling another track.
For outbound trains, an immediate “occupied” signal is needed – the sooner an operator knows a
train is moving, the better. The LOC3 signals “occupied” immediately when the laser beam is broken.
On the other hand, for inbound trains, it's necessary to wait briefly before signaling “vacant.” If too
quick, or if gaps between cars are detected, the operator might stop an inbound train before it clears the
throat. Likewise, the SYC3 (if used) would shut off track power – immediately stopping the train before it
is in the clear.
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The LOC3 has switch-selectable delays of one to five seconds before signaling “vacant.” The laser
beam must remain steady and unbroken on the photocell for the selected number of seconds before the
LOC3 considers the throat truly vacant.
This delay affects mainly inbound trains. An operator (or the SYC3) will continue running the train
until the “vacant” signal occurs. If the delay is set to five seconds, the inbound train will run for five
seconds after its caboose clears the yard throat.
This might be an issue if the train is close to its maximum length for the selected track. At a scale
speed of 25 mph, an HO scale train travels only 0.4 feet in one second, but in five seconds it travels 2.1
feet. Will the extra 1.7 feet result in the train hitting the end of the track?
(The delay is not relevant for outbound trains. The throat simply remains “occupied” for a few
seconds after the train has left the yard.)
Covering the throat
Detecting a train's presence in a yard throat is not a trivial task. Short trains and even individual
engines or self-propelled cars must be detected. To accomplish this, the LOC3's laser beam must cover
the entire throat.
Figures 15 and 17 illustrate how to design a yard and arrange the laser, photocell, and mirrors so the
beam covers the entire yard throat. Figures 16 and 18 show how to arrange them for less-than-optimal
yards.
These diagrams show gaps in the track for electrical isolation. The gaps are needed only if you want
to switch power on and off to individual yard tracks, as the SYC3 does. The gaps have absolutely
nothing to do with occupancy detection – the LOC3 does not sense electrical current. The gap between
the main track and the yard throat is optional – there is no reason these two blocks can't be wired
together. The gap is shown to help distinguish the yard throat.
Figure 15: Simple yard throat.
Figure 15 shows a simple yard with a very desirable property: The throat tracks are short and roughly
the same length. This allows the laser to shoot straight down the ladder, so that any train – even a single
engine – will break the beam (“occupied”).
Another benefit of a simple ladder like this is that the laser beam is angled relative to the train. This
minimizes the likelihood that the beam will shine through gaps between cars. With this reduced chance
of false “vacant” detection, the LOC3's delay can be set to a short time. This may sound trivial, but the
LOC3 Dual Laser Occupancy Detector User Manual
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delay represents the time between when a train clears the throat and when the LOC3 signals “vacant.” A
train can travel quite a distance in 4 or 5 seconds, so a shorter delay is better.
Figure 16: Unequal-length throat tracks.
Figure 16 is similar to Figure 15, but the yard tracks are all the same length, causing the throat track
lengths to vary considerably. Now a single laser beam down the ladder doesn't cover the entire throat.
Instead, a mirror must redirect the beam straight across the right end of the throat. The distance between
the two beams sets the length of the shortest train that can pass through the throat while continuously
breaking the laser beam for an “occupied” signal. A short train can become “lost” while moving between
the beams, causing a false “vacant” signal.
Another drawback to this arrangement is that the straight-across laser beam can shine through gaps
between cars when the angled beam is not interrupted, again causing false “vacant” signals, or
mandating that a longer-than-optimal detection delay be set.
If your yard is already built with this arrangement, the laser pointing in Figure 16 will work fine. Just
be aware of the shortcomings, and set the detection delay accordingly.
Figure 17: A symmetrical yard .
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Figure 17 illustrates a yard based on the principles described for Figure 15. The throat tracks are
short and roughly the same length, and only two mirrors are needed for the laser beam to cover the
entire throat. This arrangement offers all of the benefits as Figure 15, with only minimal additional effort
to set up.
Figure 18: Symmetrical yard with equal-length yard tracks.
This yard has the same drawbacks as Figure 16, and needs three mirrors instead of the two in Figure
17 – extra work and materials with a negative benefit. Try to avoid this kind of yard arrangement.
Again, as with Figure 16, if your yard is already built like this, the laser pointing shown here will work.
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CHAPTER 4 – INSTALLING AND WIRING THE LASERS AND PHOTOCELLS
You need one laser and one photocell for each yard, along with any mirrors identified in the planning
phase. With locations identified for these components, it's time to install and wire them to the LOC3.
What wire to use
For each yard, you will need two wires from the LOC3 to the laser two wires to the photocell, and two
wires to the equipment receiving the LOC3's detection output (e.g., SYC3). These may be individual wires, but
cables containing multiple wires are more convenient.
Network cable
Computer networking cable is ideal for this purpose. Commonly known as “Ethernet” cable or simply
“CAT5” or older “CAT3”) cable, it contains four pairs of wire, with each pair twisted together. The wires may
be solid or stranded – both will work equally well. CAT5 cable is readily available at stores such as Lowe's,
Best Buy, Radio Shack, and others. If you have some older CAT3 cable, that will work fine, too.
Figure 19: CAT5/CAT3 network
cable.
Each wire pair is color-coded. One wire has a solid color (e.g., blue) and the other wire is white with a
matching color (e.g., white/blue).
The wires fit loosely inside a plastic jacket, and often it's possible to pull them out and use just the wire
pairs, without the bulk of the jacket and unused wires. This might be helpful in some cases, but using the
entire cable – even with unused wires – is much easier.
Important: If using the entire cable, be sure to remove at least 9” of the jacket at both ends to reduce
strain on the LOC3 pin header connectors as well as the laser and photocell. Secure the cable nearby – don't
let it hang from the connectors or the laser and photocell.
Telephone cable
Telephone cable also is ideal. It's small and inexpensive, and contains four wires, each with a distinct
color.
LOC3 Dual Laser Occupancy Detector User Manual
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Figure 20: Telephone cable.
Hookup wire
You also may use individual lengths of 22- or 24-gauge hookup wire, but this can result in a “rat's nest”
of wires under the layout, which makes it difficult to track down a problem.
Ethernet (CAT3/CAT5) cable or telephone cable is strongly recommended over individual hookup wires.
Wiring pin header connectors
Lasers, photocells, and equipment using the LOC3's occupancy detection signals are wired to the
PCB with connectors that plug onto the pin headers. These connectors consist of a plastic housing that
holds contacts to which wires are attached.
The metal contacts are designed to be crimped onto wires using a special tool, then inserted into the
connector housing. However, you can use the following procedure to crimp and solder the wires without
the special tool.
1. Cut each contact from its connecting strip. Strip about 1/8” of insulation from a wire. Lay the wire
into a contact so that the bare end extends to the smaller set of crimping tabs. Use needlenose pliers to
bend these small tabs over and hold the wire in place, as shown here.
Figure 21: Bend small tabs to hold wire
against contact.
2. Touch your soldering iron to the small tabs and the wire, and solder the wire to the contact; the
solder should flow under the small tabs. When cool, use pliers to bend the large tabs over the wire
insulation. The result should look like Figure 22.
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Figure 22: Solder wire to contact, bend
large tabs over insulation.
Note: J3 and J5 require two wires on the contact inserted into pin 3 (see Figure 24). For this, twist the
bare wires together and solder both to the contact. Bend the large tabs over both wires' insulation.
3. Insert the contact into a large hole in a connector housing. Orient the contact so the tiny prong
projecting from its back side will engage the rectangular slot on one side of the housing, as shown here.
Use a small screwdriver to push the contact fully into the housing until the prong snaps into the slot.
Figure 23: Insert contact into the housing.
Laser and photocell wiring
The laser is wired to pins 1 and 3 of a connector that plugs onto J3 or J5 on the LOC3. The photocell is
wired to pins 2 and 3 of the same connector. As you can see, two wires go to pin 3. The easiest way to
accomplish this is to use one cable for the laser and a second for the photocell, and solder the two common
wires to the connector's metal contact. Running separate cables to the laser and photocell is simpler than
running one cable to the laser, and then extending two wires from it to the photocell.
Figure 24: Laser and photocell wiring with separate cables.
LOC3 Dual Laser Occupancy Detector User Manual
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Figure 24 illustrates how to wire the laser and photocell using separate cables. Here are important points
to know:

The laser's red wire (positive voltage) goes to J3/J5 pin 1.

The laser's black wire (common) goes to J3/J5 pin 3.

The photocell's short lead (positive) goes to goes to J3/J5 pin 2.

The photocell's long lead (common) goes to goes to J3/J5 pin 3, along with the black common
wire from the laser.

Figure 24 shows heat-shrinkable insulating tubing on the laser's wires that is ready to be slid over
the soldered connections and shrunk, to prevent a short-circuit there. Insulate these connections.

Likewise, longer insulating tubing should be used on the photocell's leads. It was omitted in the
photo to clearly show the connections.

Make up the laser and photocell cables with connectors as described above. Mark a
permanent dot on each connector's pin #1 (Laser) position. You will use this to ensure correct
orientation when plugging the connector onto the header. For future reference, print this page and
write in these tables the wire colors in the cables you used for the connections. Be sure to label
both ends of each cable.
Yard Name:
LOC3 J3 Pin
Connection
1 (Laser)
Laser red lead
2 (PCell)
Photocell short lead
3 (Com)
Laser black lead
3 (Com)
Photocell long lead
LOC3 J5 Pin
Connection
1 (Laser)
Laser red lead
2 (PCell)
Photocell short lead
3 (Com)
Laser black lead
3 (Com)
Photocell long lead
Wire Color
Yard Name:
Wire Color
Detector output wiring
The LOC3's two detection outputs (J2 and J4) can connect to other equipment using one of two
interface configurations. In order to choose the right one, you'll need to know what your equipment
expects.
This section describes the interfaces and how to configure the LOC3 for each. Some of the terms are
technical, but hopefully your equipment's user instructions uses similar terms.
The LOC3 has “optically-isolated” outputs on the detection outputs, J2 and J4. If the equipment
connecting to these outputs has its own optical isolator, we must omit the isolator on the LOC3.
To establish a convention, the term “isolated” output means that the LOC3 has its optical isolator
(U5 or U6) installed, and “direct” output means that the LOC3 does not have its optical isolator (U5 or
U6) installed.
LOC3 Dual Laser Occupancy Detector User Manual
Page 36
Isolated output
Refer to Figure 25. Here, the other equipment does not contain an optical isolator, so the LOC3 must
have one. Connecting pins 1 and 2 on the other equipment signals an “occupied” state to the other
equipment, and this is exactly what the LOC3 does.
Figure 25: LOC3 isolated output.
If your equipment's instructions say that it can connect to an “open-collector transistor” or relay
contacts, then the LOC3 needs the isolated output. This “open-collector” or “relay contacts” interface is
very common. Just be sure that your equipment expects a circuit closure to signal “occupied.”
Direct output
Refer to Figure 26. Here, the other equipment does contain an optical isolator. Since one isolator
cannot feed another without additional components, we must replace the LOC3's isolator with jumper
wires.
The SYC3 has its own optical isolator. If you are interfacing to an SYC3, use this direct output
configuration when assembling the LOC3. Remember the instructions on page 16.
It is more common for equipment not to have an isolator, but having one, like the SYC3, is better
practice. The isolator protects the delicate logic circuits from voltage spikes that might be picked up by
the cable between the LOC3 and the equipment. Without the isolator, the spikes are fed directly into the
logic circuits. The LOC3 has a buffer, so its logic circuits are protected in the direct output configuration.
With the direct output, the LOC3 applies +5V to pin 1 of J2 or J4 to signal “occupied,” and 0V
(connected to common) to signal “vacant.” Verify that your equipment will work with these voltage levels,
and doesn't require some other voltage like 9V or 12V. The LOC3 has no provision to produce a different
voltage or a negative voltage. Also, the +5V “occupied” signal is not capable of actuating an external
relay.
Make up the detector output cables with connectors as described above. Mark a permanent dot
LOC3 Dual Laser Occupancy Detector User Manual
Page 37
or “X” on each connector's pin #1 position. You will use this to ensure correct orientation when plugging
the connector onto the header. Print the following page and write in the table the wire colors in the cables
you used for the detector output connections. Pins for he SYC3 and older, but functionally-identical,
SYC2 are included for convenience.
Be sure to label both ends of each cable.
Detector Outputs Table
Yard Name
LOC3
SYC3
Header, Pin Header, Pin
SYC2 Pin
J2, 1 (X1)
J3, 1 (OcX)
J3, 8 (D1)
J2, 2 (Y1)
J3, 2 (OcY)
J3, 9 (D2)
J4, 1 (X2)
J3, 1 (OcX)
J3, 8 (D1)
J4, 2 (Y2)
J3, 2 (OcY)
J3, 9 (D2)
Other Equipment
Connector, Pin
Wire Color
While making and connecting the cables, take a moment to write each yard's town name in the
rectangles printed on the PCB near the pin headers, such as in this photo.
Figure 27: Town names written on PCB.
Testing the laser and photocell wiring
Check out one “town” (laser and photocell) at a time. J3 is associated with yellow LED1 and red
LED2. J5 is associated with yellow LED3 and red LED4.
 Plug the laser/photocell cable onto the relevant pin header. Be sure that the mark you applied to
each connector (page 36) matches the Laser pin.
 Turn on the power. All four LEDs should turn on and the laser should begin flashing.
 Point the laser into the end of the photocell and hold it steady. The relevant yellow LED should
blink off each time the laser flashes (the blink is quick, so it might be hard to see). After the laser
has been aimed at the photocell for the number of seconds set by the JB1 shunt, relevant red
LED should turn off. Remove the laser from the photocell, and the red LED should turn on.
 If the yellow LED is not illuminated and blinking, it is likely that strong ambient light is
overpowering the photocell while the laser is off. Adjust the relevant potentiometer (R3 for
J3/LED1, R9 for J5/LED3) until it does.
 Move the JB1 shunt to various delay times, and repeat the previous step for each delay. Measure
or estimate the number of seconds that pass between striking the photocell with the laser and
when LED2 turns on. This delay should correspond to the shunt position on JB1, as labeled on
the PCB. If the shunt is removed entirely, the delay is five seconds.
 Use the JB1 shunt to select the detection delay you want, and leave it there. To prevent loss of
the shunt, press it on any one pin of JB1 if you want the five-second delay.
After testing both lasers and photocells, you can install them on your layout.
LOC3 Dual Laser Occupancy Detector User Manual
Page 38
Laser mounting
Each yard's laser and photocell (and mirrors, if any) must be mounted securely so the laser beam
reliably hits its target. At the same time, the laser, photocell, and mirrors should be adjustable so the
beam can be aimed accurately. You might want to read Aiming the laser before fabricating your
mounting.
In Figure 28, the laser is attached to the side of a wooden block (a short length of 1x2 stock). A ¼”
hole is bored vertically through the block to attach it to the layout benchwork with a length of ¼”-20
threaded rod. This allows pivoting the block to aim the laser. A nut on the top of the threaded rod holds the
block firmly in place.
Figure 28: Laser mounting.
Notice that the laser is attached with a metal clip made from part of a cylindrical fuse holder. Secured
to the block with a single screw, the clip can be swiveled to aim the laser up or down.
It is very important to be able to adjust the laser up and down, since it's nearly impossible to attach it
and the photocell at exactly the same height. Also, wooden mounting blocks “move” with changes in
temperature and humidity, so you need to be able to quickly adjust the laser pointing when this happens.
Photocell mounting
Glue the photocell inside a hole drilled horizontally through a wooden block like the one used for the
laser. This shields it from ambient light. The ¼” pivot hole is bored off-center so it clears the photocell.
Figure 29:
Photocell
mounting.
LOC3 Dual Laser Occupancy Detector User Manual
Page 39
Mirror mounting
Figure 30 shows a mirror glued to a similar wooden block with a pivot hole. This 1” x 1” mirror was cut
from a drugstore makeup mirror using a glass cutter.
Figure 30: Mirror
mounting.
 Install the laser, photocell, and any mirrors in their designated locations, and connect the cable to
J3 or J5 on the LOC3.
Do not turn on power to the LOC3 until the next section.
Aiming the laser
In this section, we aim the laser at the photocell and verify that yard throat detection works.
 Ensure that no one can look directly into the laser beam when power is applied. This is
especially important when reflecting it with mirrors.
 Temporarily cover the laser end with a piece of cardboard, then turn on the power. Carefully
remove the cardboard from in front of the laser and look at the yard throat to determine where the
beam is headed.
 Place a piece of white cardboard in front of the photocell. Rotate the laser (and mirrors, if any)
until the red dot appears on the cardboard. Keep adjusting until the dot falls approximately where
the photocell is located behind the cardboard.
 Remove the white cardboard and adjust the laser/mirrors until the beam goes into the photocell
hole and strikes the photocell. If necessary, rotate the photocell so the beam goes straight in, and
doesn't illuminate the hole wall. If you can not get the beam to strike the photocell, read Finetuning the aim below for tips on accomplishing this.
 Look at the relevant LEDs on the LOC3 PCB. The yellow LED should be blinking off in
synchronization with the laser, and the red LED should be off, since the yard throat is vacant.
Interrupt the laser beam with your hand or other object. The red LED should immediately turn on
(throat is occupied). Remove the obstruction from the laser beam, and the red LED should turn
off after the delay set by the JB1 shunt.
 Turn off the power and repeat these five steps for the other yard throat.
Your LOC3 is operating properly, and is detecting occupancy in both yard throats.
Fine-tuning the aim
It is possible – even likely – that the laser beam does not strike the photocell. Maybe it's too high or
LOC3 Dual Laser Occupancy Detector User Manual
Page 40
too low, or way off to one side. Aiming the laser accurately can be tricky and time-consuming. These tips
might be helpful.
Aiming factors
 The laser beam travels a great distance across the yard throat, so a miniscule adjustment
moves the beam a great deal at the target. For example, suppose the laser and photocell
are 10 feet apart. Rotating the laser only 0.2º moves the spot ¼” at the photocell. That's
approximately the full diameter of the photocell, so a 0.1º rotation might be needed to
bring the spot dead-on.
Even if your yard throat is small (say, four feet), it takes only a 0.3º rotation to move the spot the
same ¼” at 48”.

If the beam is not centered vertically, possibly your benchwork is not exactly true. Add shims of
cardboard or wood under the low component's mounting block to raise it.

Use sturdy hardware to attach the mounting blocks to the benchwork. ¼”-20 threaded rod works
well, and can be screwed directly into a hole in the benchwork wood if the hole is tapped ¼”-20 to
accept the rod. This avoids drilling a clearance hole completely through the edge of a benchwork
member, and using a bolt and nut. It also allows the fastening nut to be placed on top of the
mounting block, where it can be tightened after an adjustment.

Consider attaching the laser to its mounting block with a bracket that can be swiveled up and
down, as shown in Figure 28. This is especially convenient for tiny vertical adjustments. Use
shims to get close, then zero-in by swiveling the laser on its mounting.

Place white cardboard in front of one mirror at a time to find and center the laser beam on that
mirror. Start with the first mirror, and adjust the laser. Then check the second mirror, and adjust
the first mirror to center the beam on the second. Repeat until you reach the photocell; adjust the
final mirror to center the beam on the photocell. When done, any tweaking can be done at the
laser – it's unlikely that the mirrors will need further adjustment.

Take steps to minimize wood movement due to humidity changes. If you're using wooden
mounting blocks, seal them – especially the end grain – with sanding sealer or several coats of
varnish.
Mirrors

Mirror mounts should be rotatable, just like the laser and photocell mounts.

Mirrors should be mounted exactly perpendicular to the laser beam. Otherwise, the beam will be
reflected up or down, and you'll end up shimming the laser or photocell to compensate.

Another source of movement is the layout benchwork itself. Seal the benchwork under the yard
throats if possible, or consider adding a length of steel angle iron beneath the laser path.
Finally....

Some laser modules have the capability of focusing the beam by rotating the lens on the end of
the cylinder, either with a finger and thumb, or with a large flat-blade screwdriver. Use care trying
to turn the screwdriver-slot focuser. Some are hard to turn.
It is better for our purpose if the beam is unfocused, and not a pinpoint. An unfocused beam
produces a larger spot, which is less-critical to position on the photocell. This might be an oval instead of
a perfect circle, but that's okay. As disconcerting as this might be for the compulsive among us, the oval
works fine – it's easily bright enough to activate the photocell.
I recommend leaving the laser unfocused, or de-focusing one that produces a tiny spot.
LOC3 Dual Laser Occupancy Detector User Manual
Page 41

Once the lasers are aimed, you can expect the LOC3 to operate reliably each time it is poweredup. If the LOC3 indicates that a yard throat is occupied when it is not (red LED on when it should
be off), the first thing to check is whether the laser beam is striking the photocell. Look at the
photocell and adjust the laser to center the spot.
Congratulations! Your LOC3 is installed on your railroad, and is ready for service. All that
remains is to connect it to your SYC3 or other equipment needing the occupancy signals.
Connecting the LOC3 to other equipment
As mentioned earlier, the LOC3 works seamlessly with the SYC3 Staging Yard Controller (see page
6), but it also can connect to other equipment needing “occupied” and “vacant” indications for yard
throats – it is not limited to the SYC3.
This section first explains how to connect the LOC3 to an SYC3, then gives generic instructions for
connecting the LOC3 to other (unknown) equipment. For the latter, you must refer to your equipment's
instructions to determine the connections to be made.
Connecting the LOC3 to an SYC3
This section tells how to connect the LOC3 to an SYC3 (or older, but functionally-equivalent) SYC2
Staging Yard Controller. For convenience, “SYC” is used to refer to either one.
 Refer to the SYC user manual, and ensure that your SYC is operating properly with no
occupancy detector connected.
 Refer to Direct output on page 37, and the Detector Outputs Table you completed on page 38
when you made up the detector output cables. Plug one of these cables into the LOC3's J2 or J4,
and the other end into an SYC3' J3. Ensure by looking at wire colors that the LOC3's “X” (X1 or
X2) pin connects to the SYC3's J3 OcX pin (SYC2: J3-8, D1), and that the LOC3's “Y” (Y1 or Y2)
pin connects to the SYC3's J3 OcY pin (SYC2: J3-9, D2).
 Power-up the LOC3 and SYC3 (SYC2). With the laser covering your yard throat and striking the
photocell, the SYC's red LED should illuminate, indicating that the SYC is awaiting a track
selection an train movement.
 Interrupt the leaser beam with your hand or other object. The SYC's red and green LEDs should
begin flashing alternately, indicating that the SYC has detected something unexpected in the yard
throat. Remove the obstruction, and the flashing should stop, with the red LED remaining
illuminated. This confirms that the LOC3 is correctly signaling the SYC.
 If you'd like additional confirmation, select a track with the SYC's switch, then press the SYC's
Start button. The SYC's green LED should come on,meaning it's okay to move a train through
the throat.
 Interrupt the leaser beam with your hand or other object. The SYC's yellow LED should turn on
(SYC2: yellow and green LEDs both illuminate), indicating that the SYC has detected a “train” in
the throat.
 Remove the obstruction. The SYC's yellow LED (SYC2: yellow and green LEDs) should turn off,
and the red LED should turn on, indicating that the “train movement” is complete.
 Repeat these steps for your other staging yard and SYC, connecting the cable to the LOC3's
other detector output header J2 instead of J4, or J4 instead of J2).
Connecting the LOC3 to generic equipment
This section tells how to connect the LOC3 to other equipment that needs an occupancy signal. By
necessity, these instructions are generic, and you must refer to your equipment's instructions to
understand how it works, and what connections are needed.
LOC3 Dual Laser Occupancy Detector User Manual
Page 42
 Refer to the equipment's user manual, and ensure that it is operating properly with no occupancy
detector connected.
 Refer to the Detector Outputs Table you completed on page 38 when you made up the detector
output cables. Plug one of these cables into the LOC3's J2 or J4, and the other end into your
equipment's detector input. Ensure by looking at wire colors that the LOC3's “X” (X1 or X2) pin
connects to your equipment's “positive” or “input” pin, and that the LOC3's “Y” (Y1 or Y2) pin
connects to your equipment's “common” or “ground” pin.
 Power-up the LOC3 and your equipment. With the laser covering your yard throat and striking the
photocell, your equipment should indicate “vacant.”.
 Interrupt the leaser beam with your hand or other object. Your equipment should indicate
“occupied.”
 Remove the obstruction. Your equipment should indicate “vacant.”
Congratulations! You have successfully integrated the LOC3 into your railroad, and it is ready
for service.
LOC3 Dual Laser Occupancy Detector User Manual
Page 43
SCHEMATIC DIAGRAM
LOC3 Dual Laser Occupancy Detector User Manual
Page 44
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