LNLD Differential Amplifier Remote Control Interface (SP 1`004a)

LNLD Differential Amplifier Remote Control Interface (SP 1`004a)
Physics Basel
Electronic Lab
Klingelbergstr. 82
CH-4056 Basel
Switzerland
SASCHA LINDER & MICHAEL STEINACHER
0041 61 207 37 21 (22)
TEL:
0041 61 207 37 84
FAX:
SASCHA.LINDER@UNIBAS.CH
E-MAIL:
MICHAEL.STEINACHER@UNIBAS.CH
E-MAIL:
HTTP://WWW.PHYSIK.UNIBAS.CH
WEB:
LNLD Differential Amplifier
Remote Control Interface (SP 1’004a)
User’s Manual | Revision 1.1 | June 2016
Features
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Fits to the LNLD Differential Amplifier (SP 1’004)
Helpful if the Differential Amplifier is difficult to access
Remote control of gain and LP cut-off frequency
Reads and displays the Overload LED
Reads and displays the Offset Compensation LED
Intuitive operation with a color backlighted touchscreen
No deterioration of noise performance of the amplifier
Also controllable by simple ASCII-commands via serial port
Restores the last settings at power up
Small size (130 x 70 x 40 mm), low weight (190 g)
4 meters 10 pin interconnection flat cable included
3 meters 9 pin D-SUB RS-232 cable (1:1) included
Wide input (100…240 VAC) wall-plug power supply included
Description
To reach the best noise performance of the Low Noise Low Drift Differential Amplifier (LNLD Diff Amp) it
is recommended to install it as close as possible to the sample. That’s why the device is often mounted
directly on the break-out box on top of the cryostat. So it may be difficult to access the knobs on the
front panel where the gain and the low-pass filter cut-off frequency are selected. Further the important
red Overload and green Offset LED may not be visible.
For such installations this Remote Control Interface (SP
1’004a) is a helpful device. It allows controlling the gain
and the low-pass filter cut-off frequency remotely and it
also displays the status of the Overload and Offset
Compensation LED.
By pressing the corresponding field on the touchscreen
(see photo on the left) the GAIN and LP-Filter settings
are remotely changed. Since the fields are on the touch
screen are pretty small, the operation with the fingernail
is proposed. The Overload indicator changes its color
from gray (OFF) to red (ON) if the amplifier gets
overloaded. The Vin Offset Compensation indicator
changes its color from gray (OFF) to green (ON) if the input stage of the amplifier is compensated. The
actual settings are periodically stored and after power up the last settings are automatically recovered.
The booting of the device takes around one and a half minute; during the booting phase the gain is set
to 1’000 and the cut-off frequency may varying.
User’s Manual Rev 1.1
LNLD Diff Amp Remote Control Interface (SP 1’004a)
Page 1 of 5
In parallel to the manual touch-control of the GAIN and LP-Filter settings the device can also
communicate via a standard RS-232 serial port with a computer. By sending simple text commands
(ASCII) the GAIN and LP-Filter settings can be altered and the actual settings (GAIN, LP-Filter, Overload
and Vin Offset Compensation) can be readout.
Settings and Connections
While using the remote control interface it is important that the two rotary switches on the LNLD Diff
Amp (SP 1’004) are set to the position “Remote” (see photo on the left). The GAIN has to be in the
position “x1’000, Remote” and the fcut must be set to the position “100Hz, Remote”
If local settings (by the two rotary switches) are preferred the cable at the Remote Control I/O
connector has to be disconnected or the remote control
interface has to be turned off.
The Remote Control I/O connectors (10 pin) of the
remote control interface and the LNLD Diff Amp have to
be interconnected by a 1:1 cable (see below). A 4 meter
long flat interconnection cable is included and it is
equipped on both sides with the suitable connectors
(Minitek 2x5P, 89947-710LF). Note that the plugs are
coded with a recess on the upper side and the connector has a central key which must be orientated to
the upper side of the devices so that the flat cables leave the connectors on the top.
10 pin cable 1:1 (4 m)
Serial-port
connection 1:1
(RS-232)
The remote control signals are galvanically isolated by optocouplers inside the LNLD Diff Amp.
Therefore no ground-loops or interference can occur when using the remote control interface.
Nevertheless, make sure that no high-frequency noise is coupled into the remote control I/O
interconnection cable. Otherwise the high-frequency noise may capacitive coupling into the sensitive
electronics of the amplifier. In low-interference laboratory environment an unshielded flat cable up to a
length of around 5 meters should be fine. If the remote control cable has to travel over a large distance
in noisy environments, a shielded interconnection cable between the remote control interface and the
LNLD Diff Amp may be necessary.
For further information about the remote control see the datasheet of the LNLD Diff Amp (SP 1’004),
chapter “12. Remote Control”.
The included wide input (100…240 VAC) wall-plug power supply (HNP10ImicroUSB, 5 V, 2.1 A) has to be connected to the remote control interface on
the top right side (see left).
Make sure that the orientation of the microUSB connector and the plug are
correct before connecting.
The remote control interface can be turned off by disconnecting this
connector or by switching off the mains of the wall-plug power supply.
User’s Manual Rev. 1.1
LNLD Diff Amp Remote Control Interface (SP 1’004a)
Page 2 from 5
Serial Communication
Besides the manual selecting of the GAIN and the LP-Filter cut-off frequency, the remote control
interface can also communicate with a computer. The communication between the remote control
interface and the computer works via a serial connection using the RS-232 standard. A 9 pin D-SUB
cable with a 1:1 wiring has to be used for the interconnection. Such a cable with a length of 3 meters is
included. The settings of the serial port are the following:
Baudrate = 9’600
Databits = 8
Stopbits = 1
Parity = None
Flow control = None
A simple text communication (ASCII - which is not case sensitive), is used for data transmission.
Therefore a terminal program (e.g. putty, running on a PC) can be used for testing the communication.
If a command cannot be correctly interpreted, the remote control interface sends a help text-string.
SET Commands
The GAIN and the LP-Filter cut-off frequency of the LNLD Diff Amp can be programmed by sending the
ASCII commands “SET”. Each command must be terminated by a Carriage-Return <CR> (0x0D). When
the command was correctly interpreted, the remote control interface responds with an “OK” followed
by a Carriage-Return <CR> (0x0D) and a Line-Feed <LF> (0xA).
To set the GAIN, the following command must be used:
“SET G” followed by a <SPACE> and then the desired gain “1E2”, “1E3”, “1E4” or “100”, “1000”,
“10000” ended with a <CR>.
For example, to set the GAIN to 100 the following ASCII command must be used:
SET G 100 <CR> or SET G 1E2 <CR>
The device responds with:
OK <CR> <LF>
To set the LP-Filter cut-off frequency, the following command must be used:
“SET F” followed by a <SPACE> and then the desired LP-Filter cut-off frequency (100 Hz…1 MHz/full) and
ended with a <CR>. The cut-off frequency can be typed with Hz or without and the “k” is interpreted
correctly.
For example setting the LP-Filter cut-off frequency of the amplifier to 1 kHz can be done with one of the
following commands:
SET F 1000 <CR>
SET F 1000Hz <CR>
SET F 1k <CR>
SET F 1kHz <CR>
In all cases above the device responds with:
OK <CR> <LF>
To set the LP-Filter cut-off frequency of the amplifier to its maximum 1 MHz (full) the following
command must be used:
SET F FULL <CR>
The device responds with:
User’s Manual Rev. 1.1
LNLD Diff Amp Remote Control Interface (SP 1’004a)
Page 3 from 5
OK <CR> <LF>
GET Commands
By using the “GET” ASCII commands the actual settings of the amplifier can be read out. The command
must be terminated by a Carriage-Return <CR> (0x0D). When sending “GET” without a parameter the
remote control interface responds with the GAIN, the LP-Filter cut-off frequency and the status of the
Overload and Offset Compensation LED on four separated lines; each line is terminated with a CarriageReturn <CR> (0x0D) and a Line-Feed <LF> (0xA).
For example, when the LNLD Diff Amp is actually set to a GAIN of 1’000, the LP-Filter cut-off frequency
is set to 1 kHz, the Overload LED is turned OFF and the Vin Offset Compensated LED is turned ON, the
“GET” command reads the following:
GET <CR>
The device responds with:
Gain: 1000 <CR> <LF>
Filter: 1kHz <CR> <LF>
Overload: OFF <CR> <LF>
Vin Offset Compensated: ON <CR> <LF>
To read-out only the actual GAIN, the command “GET G” must be used:
GET G <CR>
The device responds with:
Gain: 1000 <CR> <LF>
To read-out only the actual LP-Filter cut-off frequency, the command “GET F” must be used:
GET F <CR>
The device responds with:
Filter: 1kHz <CR> <LF>
To read-out only the actual Overload status, the command “GET O” must be used:
GET O <CR>
The device responds with:
Overload: OFF <CR> <LF>
To read-out only the actual Vin Offset Compensated status, the command “GET C” must be used:
GET C <CR>
The device responds with:
Vin Offset Compensated: ON <CR> <LF>
User’s Manual Rev. 1.1
LNLD Diff Amp Remote Control Interface (SP 1’004a)
Page 4 from 5
Commands Send Automatically
When a changing Overload or Offset Compensated status is detected, a text message is automatically
send via the serial port. This allows that an attached computer can react on the Overload state
transition and automatically changes the GAIN [V/A], for example.
When the Overload status changes from OFF to ON, the following message is send automatically:
Overload: ON <CR> <LF>
When the Overload status changes from ON to OFF, the following message is send automatically:
Overload: OFF <CR> <LF>
When the Offset Compensated status changes from OFF to ON, the following message is send
automatically:
Vin Offset Compensated: ON <CR> <LF>
When the Offset Compensated status changes from ON to OFF, the following message is send
automatically:
Vin Offset Compensated: OFF <CR> <LF>
Background
The remote control interface is based on a single-board computer “Raspberry Pi B+” running a Linux
operation system. The 2.8” touchscreen has a resolution of 320 x 240 pixels and comes from the
company “Adafruit”. The application of remote control interface is written in the programming
language “Phyton”.
User’s Manual Rev. 1.1
LNLD Diff Amp Remote Control Interface (SP 1’004a)
Page 5 from 5
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