Skin Conductivity Circuit- HELP PLS!

I built a circuit using an arduino uno that measures skin conductivity. It has two electrodes connected to two different fingers. A 5 volt current is sent through the electrode on one finger, then the second electrode connects back to the A0 port in order to read the current. This should tell you how much your body is resisting the initial 5v current. I based my circuit off of a website online (http://ftmedia.eu/diy-gsr-sensor/) that said to use a 0.1uf capacitor as well as a 10k resistor to "reduce noise". However, when I try to read the value, i keep on getting 0's.

Here is a pic of the ciruit: Imgur: The magic of the Internet

Test your electrodes by connecting a 10K Ohm resistor between them. If everything is OK, you should get a reading of about 2.5V (about 512 analogRead value).

A 10K resistor seems way too small. Try 1M or 10M.

The resistance between your fingers will be in the megohms. With your body resistance as the "top" of a [u]voltage divider[/u] and 10K as the "bottom" resistor, almost all of the voltage will be dropped across your body with almost zero measured across the resistor.

I tried using the 10k resistor between the electrodes and left the circuit exactly how it is now and I got a consistent reading of 30 from the serial monitor. Then when I placed my fingers on the electrodes I kept getting 0's.

Also, I tried removing the capacitor and resistor from the circuit, and put my fingers on the electrodes and got values from 300-600 on the serial monitor, and then got 1023 when I tried putting a 10k resistor across the electrodes.

Any idea why this is happening? Do the resistor+capacitor that are put in the circuit to reduce noise, at too high of a resistance or something causing my readings to be too low?

Any idea why this is happening?

Yes, we could have predicted all your results, they are exactly as expected, except this one:

I tried using the 10k resistor between the electrodes and left the circuit exactly how it is now and I got a consistent reading of 30 from the serial monitor.

From your description, you should have got a reading around 512, not 30. So I think you have not wired up your circuit correctly. Post a schematic diagram please. Hand drawn is ok.

You should read up on "voltage dividers" on Google, then try the suggestions you have been given.

anjaleen:
IAlso, I tried removing the capacitor and resistor from the circuit, and put my fingers on the electrodes and got values from 300-600 on the serial monitor, and then got 1023 when I tried putting a 10k resistor across the electrodes.

Any idea why this is happening? Do the resistor+capacitor that are put in the circuit to reduce noise, at too high of a resistance or something causing my readings to be too low?

Without the capacitor and resistor you get true readings. Only fix what's broke. If the reads jitter then try the cap but not until.

These can vary on the mood of a person, that is how polygraph tests work.

1023 on a 5V Arduino means 5V, it is the highest analog read value. You should have gotten a smaller number with 10K between.

1023 on a 5V Arduino means

...just slightly less than the reference voltage.

Or more which gets the same value.

Hi,
OPs picture.

Tom.. :slight_smile:
PS. Have you measured your 10K resistor, to make sure it is 10K?

anjaleen:
said to use a 0.1uf capacitor as well as a 10k resistor to "reduce noise".

The capacitor is to reduce noise. The resistor is required and acts as half of a voltage divider (with your skin being the other half).