AD630 Lock-in Module Resistor Experiment Troubleshooting

Thread Starter

Arman00

Joined Oct 25, 2021
5
Hello everyone,

I'm trying to use this board as an analog lock-in amplifier; however, I'm running into some difficulties due to a lack of any documentation on the use of this device in lock-in experiments, save for PhysicsOpenLab blog post that performs the experiment I'm trying to replicate. I've tried contacting numerous sellers on eBay for a device manual, including the seller I got the board from, but have yet to receive any documentation besides the manual for the AD630 chip itself.

The experiment:
Circuit:
1k resistor and 1-ohm resistor in series. The input signal is a 1Vpk, 1kHz square wave. I want to obtain the voltage signal across the 1-ohm resistor using the AD630 board. When I measure across the 1-ohm resistor directly with my oscilloscope, I do not get a very clear reading, as expected. The goal is to send the signal to the board and connect the output of the board to the oscilloscope. But I also get no reading this way.

I'm powering the AD630 board using a 9V battery connected to the board with 9V battery connectors. I know the board is on because a sequence of red LEDs turns on when I connect the battery. I connect the input signal (V across 1-ohm) and reference signal (square wave input) to the board and still fail to get an output. The board comes pre-configured in phase-lock mode and supposedly has a gain of 10, so I should surely be seeing something resembling a square wave, I'm only looking for millivolt sensitivity here.

Has anyone used this module in a similar experiment before?
 

michael8

Joined Jan 11, 2015
230
Why does the board have 3 power supply terminals?

basic opamps:
http://www.ece.uprm.edu/~mtoledo/5205/Docs/basic_apps.pdf

which says: Most op amps are designed to work with two supplies usually connected
to positive and negative voltages of equal magnitute (like the uA741 which works with±15V).


AD630 Analog Devices web page:
https://www.analog.com/en/products/ad630.html#product-overview

AD630 datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/AD630.pdf

Page 3 says: SPECIFICATIONS At 25°C and ±VS = ±15 V, unless otherwise noted

This is in line with normal op-amp circuits which use both positive and negative supplies
around a central 0 voltage. And power supplies are usually assumed to exist.

I'd suspect it can't work with just one voltage. How did you connect your 9 volt battery?
 

Thread Starter

Arman00

Joined Oct 25, 2021
5
Why does the board have 3 power supply terminals?

basic opamps:
http://www.ece.uprm.edu/~mtoledo/5205/Docs/basic_apps.pdf

which says: Most op amps are designed to work with two supplies usually connected
to positive and negative voltages of equal magnitute (like the uA741 which works with±15V).


AD630 Analog Devices web page:
https://www.analog.com/en/products/ad630.html#product-overview

AD630 datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/AD630.pdf

Page 3 says: SPECIFICATIONS At 25°C and ±VS = ±15 V, unless otherwise noted

This is in line with normal op-amp circuits which use both positive and negative supplies
around a central 0 voltage. And power supplies are usually assumed to exist.

I'd suspect it can't work with just one voltage. How did you connect your 9 volt battery?
The 3 terminals are for positive, negative, and ground. I connect the black wire of the 9V battery connector to the negative terminal and the red wire to the positive. I connect the board to the resistive circuit ground. According to the PhysicsOpenLab blog post, the board works with 5-18V power supply.
 

crutschow

Joined Mar 14, 2008
28,154
The 3 terminals are for positive, negative, and ground. I connect the black wire of the 9V battery connector to the negative terminal and the red wire to the positive
You need two separate supplies, each connected to circuit ground.
One 9V battery is only one supply.
 

Thread Starter

Arman00

Joined Oct 25, 2021
5
You need two separate supplies, each connected to circuit ground.
One 9V battery is only one supply.
So I use two 9V batteries and two sets of connectors (4 wires in total, 2 positive 2 negative). Do I connect the negative wires to circuit ground and the positive wires to the positive and negative power inputs of the board?
 

michael8

Joined Jan 11, 2015
230
Be careful, connecting power with the wrong polarity might damage something on your circuit board. A dual supply
looks like this:

dual-battery-supply1.png


Running off of 9 volt batteries isn't usually a good choice, they don't hold much power and will run down
with the voltage dropping as they are used. The voltage endpoint is usually considered 6V. With
two they may not run down at the same rate leaving your dual supply unbalanced. This may
or may not have an effect on your circuit.
 

Thread Starter

Arman00

Joined Oct 25, 2021
5
Be careful, connecting power with the wrong polarity might damage something on your circuit board. A dual supply
looks like this:

View attachment 251195


Running off of 9 volt batteries isn't usually a good choice, they don't hold much power and will run down
with the voltage dropping as they are used. The voltage endpoint is usually considered 6V. With
two they may not run down at the same rate leaving your dual supply unbalanced. This may
or may not have an effect on your circuit.
Thank you for the diagram. I noticed in the linked blog post that they were using 9V batteries and the board worked just fine, so I did the same to replicate their experiment. I could also use a 9V adapter and wall plug if the batteries cause issues.
 

Thread Starter

Arman00

Joined Oct 25, 2021
5
I noticed in the linked blog post that they were using 9V batteries

I missed that -- looking at it now, the only "reference" to batteries I can see is in the picture
at:
https://physicsopenlab.org/wp-content/uploads/2019/08/LockInAmpli2-768x700.jpg

This section here (no batteries, but two battery connectors):
View attachment 251219
I'm not really sure what those connectors are actually connecting to (definitely not a power supply/generator), but seeing as the board is designed for 5-18V power supply, I figured 9V batteries would be fine. For my purposes, the board won't need to be powered on for long and continuous periods, so replacing them as the voltage dwindles won't be a major inconvenience.
 
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