Electrochemistry of Plant Life
Analog to Digital Converter (ADC)
Using the arduino we can measure analog voltages using the 6 Inputs ADC. The analog voltage between 0 and 5 V is converted into a 10bit digital number, from 0 to 1023. this can be used to read a value from a sensor, eg a temperature sensor such as the TMP36, a potentiometer or from the electrodes.
Sound Card - Line In
If the potentials we want to measure are mostly changes/modulations in voltages, we can also use the analog-to-digital converter from the sound card. Although that means we cannot measure static voltages, but only fast changes changes, frequencies above ~ 1hz. The sound card is a very fast and precise ADC (single if mono, or double for stereo), sampling at 44khz or up to 96khz and 24 bit resolution.
If the signals are to low, such as µV in the example of potentials in plants, we need to amplify the signal and make sure we do not have too much noise or other garbage in our signals. INA118 is a high end instrumental amplifier, with low noise. But maybe cheaper amp might do the trick aswell, such as the LM386
If we want to measure more inputs we can multiplex them. meaning we measure one input at the time using a chip (4051), which got 8 inputs which are then routed to one single input on the arduino. read more about using the 4051 multiplexer/demultiplexer
because every conducting wire, electrode or other parts of a measurement setup are also acting kinda as "antennas", its easy to pick up some artefacts, noise, humms from the electromagnetic environment. typical stuff the measure are the 50Hz humming from all the electric power and lamps or "biipbuupbiiiiip" from mobile phones. to prevent these one can use shielded cables or build a faraday cage around the whole setup.
DIY Glass Pipette Electrodes
Getting on Plant's Nerves @ HAIP festival, Ljubljana, Nov 2010
its not electro-physiology, hehehe