I am trying to amplify the galvanic skin response of my body and am having quite the trouble doing it...I have one penny connected to the 3.3V output of the Arduino and the other penny going into the positive input of the LF353N. The LF353N is being powered by two 9V batteries (but practically at +/- 7V). I have wired a 1k resistor from the negative input to ground and a 2.2k resistor going from negative to output. In theory, this would be a non-inverting op-amp with a gain of 3.2. The experimental value of my GSR is around 0.6 V. When I measure the output of the op-amp, I get outputs that jump wildly from 0 to 1.8V. When I connect the electrodes to my fingertips, the output goes to 5.4 V. Is there some design aspect I'm ignorant of with regards to the LF353? Or perhaps something with the way I have my batteries wired that I should be aware of?
That circuit won't work as you intend, because the input impedance of the op amp is extremely high and there is no effective path to ground for the currents flowing though the skin. What you are doing is amplifying stray voltages picked up by your body.
A google image search for "galvanic skin response" will produce lots of alternative circuits (many of which will probably be poor), but the ones that work will show a resistor to ground in series with the probes. Here is one example: GSR respuesta galvánica del piel
You should use a battery to power the probes and not the Arduino power supply, to isolate potential noise sources.
I am trying to follow this schematic for a "truth meter":
Instead of using the MCP6002 I am using the MCP6004. However, I am getting nothing at the output. I am using 2 9V batteries as the V+ and V- and powering the MCP with the 3.3V arduino output. Could anyone see any potential pitfalls in the design?
