Garmin v1.0b Clock User Manual

GPS Upgrade Kit for IN-14 Nixie Clock
General Instructions
v1.0b
Instructions for Adding a Garmin GPS 18 LVC to a IN-14 Nixie Clock
 2007 Peter J. Jensen, LLC
Ann Arbor, MI
Scary Warning
DANGER: BUILDING OR MODIFYING THIS KIT
INVOLVES
WORKING
WITH
DANGEROUS,
POTENTIALLY LETHAL VOLTAGES. POWER LINE
VOLTAGES ARE DANGEROUS. IF YOU ARE NOT
EXPERIENCED WORKING WITH DANGEROUS,
POTENTIALLY LETHAL VOLTAGES, RETURN
THE KIT FOR A REFUND.
IF YOU DO NOT
ACCEPT FULL RESPONSIBILITY FOR WORKING
WITH THESE POTENTIALLY LETHAL VOLTAGES,
RETURN THE KIT FOR A REFUND.
BY BUILDING OR MODIFYING THIS KIT, YOU
ACKNOWLEDGE AND AGREE THAT PETER J.
JENSEN, LLC, AND ITS MEMBERS, BEAR NO
RESPONSIBILITY (OR AS LITTLE AS IS
PERMISSIBLE BY LAW) FOR ANY HARM TO
PERSON, PROPERTY, OR ANYTHING ELSE
ANYBODY CAN THINK OF, DUE TO YOU
WORKING
WITH
THESE
DANGEROUS,
POTENTIALLY LETHAL VOLTAGES OR BUILDING
THIS KIT.
Overview
A man with a watch knows what time it is. A man with two watches is never
sure. - Segal's Law
This document describes how to connect a Garmin GPS 18 LVC to the IN-14 Nixie
Tube Clock from tubeclock.com. The GPS unit will allow the clock to set and
maintain time display to sub-millisecond accuracy.
Timing accuracy comes from the GPS receiver in the Garmin GPS 18 hardware. The
GPS 18 receives signals from the network of satellites which orbit the Earth and
transmit accurate time codes via radio waves. These time codes are typically used for
calculating position for navigational purposes, but they also provide a highly reliable
time source.
GPS Advantages and Disadvantages
The advantages of GPS time synchronization include a high degree of accuracy over
long periods of time (it is referenced to atomic clocks), and it's ubiquitous availability
anywhere on the Earth.
The disadvantage is that the signal is very weak, so the GPS 18 hardware should be
placed in a position where it has a line of site view of the sky. The unit will work
indoors, but at least placing it on a window sill is a good idea. Even thin material, like
paper, will effect the receiver's performance. The Garmin GPS 18 LVC has a
magnetic base, and also a screw to help with mounting.
Search on amazon.com or the web for part numbers 010-10541-00 (suction cup
mount) or 010-10453-00 (flange mount) if you would like mounting hardware for the
GPS 18 LVC.
Operation
The Nixie Clock will communicate to the GPS-18 via two mechanisms: first is an RS232 serial port for communicating the time and setup information; and second is a
Pulse Per Second (PPS) signal which will keep the clock in sync when the serial
communications are not in use.
A copy of the complete GPS-18 manual can be found on the Garmin website:
http://www.garmin.com/manuals/425_TechnicalSpecification.pdf
When the clock is turned on, the GPS will take from a few seconds to five minutes to
acquire the satellites' signal. During this time, the clock will run using it's on-board
oscillator, and you will need to set it to within 15 minutes of the correct time. This is
necessary because the GPS system does not provide time zone information. When the
signal is acquired, the GPS will send a signal to the clock (by beginning strobing of the
PPS line) and the clock will then read the next serial port message and adjust the time.
Once the PPS signal has begun, the GPS unit will continue sending one pulse per
second until power is turned off, regardless of the satellite tracking state. The clock
will synchronize its second counter to this PPS signal.
In addition to setting the time on the first PPS signal, every morning at 2:45am the
clock will query the GPS unit over the serial line. It will adjust the clock to the nearest
half-hour offset of the UTC time provided from the GPS.
The GPS provides the Universal Coordinated Time (same as Greenwich Mean Time).
The clock assumes the user has set the time to within half an hour of the correct local
time (i.e., plus or minus 15 minutes) and uses the the UTC time from the GPS
calculate the exact time.
Parts
The first rule to tinkering is to save all the parts. -- Paul Erlich
Part Name
Description
PIC16F688 Microcontroller
Updated microcontroller with support for GPS
1 Watt, 100Ohm Resistor
Replaces ½ Watt, 1k Ohm Resistor R1. This will allow more 5V power supply
current to power the GPS-18
Wire
Optional, to connect nixie decimal point display to AUX_A or AUX_B driver
output. This will cause the nixie decimal point to light up a Pulse Per Second
(PPS) signal is being received
Garmin GPS 18 LVC
The GPS antenna and receiver on a 5 meter cable. Make sure the GPS-18 has
a view of the sky, as unobstructed as possible. It will work indoors, but at
least placing the unit on a window sill is a good idea.
12V DC Power Adapter
The 12V power adapter included with the GPS upgrade kit is a switch-mode
power supply. WARNING: Please make sure to use the GPS modified
clock ONLY with a switch-mode 12V power adapter, a 12V battery, or
other true 12V source. The 12V power adapter which shipped with the nonGPS kit is transformer-based, and provides too high a Voltage for the GPS
modified clock. The transformer-based power adapter can actually output up
to about 18V, which will burn out the 100Ohm dropping resistor.
If you would like mounting hardware for the GPS 18 LVC, search on amazon.com or
the web for part numbers 010-10541-00 (suction cup mount) or 010-10453-00 (flange
mount).
How To Connect The GPS
Furious activity is no substitute for understanding. -H. H. Williams
These instructions assume that you are adding the GPS upgrade to a completed IN-14
nixie clock kit purchased through tubeclock.com. If you are adding the upgrade at the
same time as building the kit, you will not need to remove the standard parts. Simply
substitute the parts that came with the GPS upgrade kit instead. If you purchased a
completed IN-14 nixie clock, you may use these instructions to upgrade the clock
yourself.
1) To provide sufficient current for the GPS unit, resistor R1 will need to be replaced.
This resistor was a ½ Watt 1k Ohm part, located on the right hand side of the PCB.
Remove R1 and replace it with the 1 Watt, 100 Ohm part provided.
2) There are six wires which lead to the GPS-18. Each of these wires connects to a
solder pad on the Nixie Clock circuit board. Snip off the connector provided on the
GPS-18, strip the wire ends, and solder them to the pads on the clock PCB as listed in
the table below.
Yellow
GPS
18
Pin #
Color
Signal Name
Wire
Gauge
Connection Point on
Clock
1
Yellow
Pulse Per Second Output
28
RA0
2
Red
Vin – 5V Power In
26
5V_A
3
Black
Ground
28
GND_A
4
White
GPS Serial Transmit
28
RC1
5
Black
Ground
26
GND_A
6
Green
GPS Serial Receive
28
RC0
Black (two wires)
Green
White
Red
Replace Microcontroller
Replace R1
with 100Ohm 1W
3) Gently pry the old microcontroller from the socket, and insert the new PIC16F688.
4) Finally, the 12V DC power adapter will need to be replaced. WARNING: the 12V
power adapter which shipped with the non-GPS kit is transformer based, and provides
too high a Voltage for the GPS modified clock. The transformer based power adapter
can actually output up to about 18V, which will burn out the 100Ohm dropping
resistor. Please make sure to use the GPS modified clock ONLY with a switchmode 12V power adapter, a 12V battery, or other true 12V source. The 12V
power adapter included with the GPS upgrade kit is a switch-mode power supply
which will work without problems.
Jumper Wire
New 100Ohm,
1Watt
Resistor R1
Optional PPS Active Indicator
5) Optionally, although recommended, you may wish to run a jumper wire from the
AUX_A pad to the decimal point indicator on the seconds nixie. This will light up the
decimal point on the right hand nixie as long as PPS signal has been received from the
GPS within the last second. Remember that the GPS takes about five minutes to
get synchronization on power-up before the PPS signal will be received.
The decimal point pins on the nixies are directly to the left and right of the bottommost pin- approximately in the 5 o'clock and 7 o'clock positions. You can use any
decimal point you wish as the indicator.
The AUX_B pad can also be used, except this pad will toggle on or off each time a
new pulse is received on the PPS line. The effect of connecting to the AUX_B pad is
the indicator will turn on for a second, then off for a second, and then repeat so long
as the PPS signal is active. If the PPS signal stops, the AUX_B connected indicator
will maintain it's last state.
Conclusion
A conclusion is the place where you got tired of thinking. - Harold Fricklestein
When you power up the GPS modified clock, with the GPS plugged into it, it will at
first appear and function as it did without the GPS. Set the time to within 15 minutes,
and let the clock run. When the GPS acquires the satellite signal, the time displayed
will correct itself, and stay locked onto the GPS PPS output from then on.
Additionally, every morning, at 2:45am local time, the clock will recheck that it has the
correct time according to the GPS unit.
If you connected the jumper wire to one of the nixie decimal places, it will light up to
indicate that the GPS has synchronization and is sending PPS signals If the GPS does
not acquire synchronization within five minutes, you may need to move the GPS
antenna to a location closer to a window, or away from obstructions.
I hope you enjoy your GPS upgrade. If you have trouble with the unit, please contact
me, Peter Jensen, at jensen@peterjjensen.com.
Update
The new revision of the the PCB has a place to put a header to mate with the
connector which is already on the GPS unit. The surface mount header is shown in
the picture below, and is now included with the GPS upgrade kit. Connecting to the
thru-hole connection points as described in this manual still works, but using the
header is a cleaner and easier method. This manual will be updated soon to reflect this
change.
In this picture the header shown is oriented with the pins facing the bottom of the
image, while it needs to be soldered into place with the pins facing the top of the
image. Make sure the six pins on the header line up with the six pads, and the two
support pins on the front of the header line up with the two support pads on the PCB
(closest to the edge of the PCB).
The board header which mates directly with the connector on the GPS 18 is
Digikey.com part number 455-1806-1-ND.