I've posted several snippetts recently in that section of the forum and have (at least) another three "in the pipleine". After each measurement the PICaxe program simply toggles the output pin. The third pin measures the voltage on the other side of the resistor, so the current can be calculated. One of the pair of linked pins drives current alternately from the supply and ground, the other pin measures the voltage across the output driver FETs (an "unknown" and potentially not negligible voltage). The other electrode goes via a capacitor to ground. So, what I would try is two PICaxe pins connected to one end of a resistor, with the other end going to a third PICaxe pin and one electrode. It's even possible to estimate the current purely by measuring the rate of change of voltage across the capacitor, but that's a rather more "advanced" method (on which I happen to be preparing a "code snippet"). Also, you then no longer need a bridge configuration. no dc) provided that there are no circuit connections which can "bypass" the capacitor. A capacitor "guarantees" that there can be no net current flow (i.e. However, there are advantages in using a capacitor (probably to ground) in series with one electrode. But the PICaxe ADC operates fully between the supply rails, so a single resistor can be used, with the resistor on one electrode measuring relative to ground or to the supply, depending on the phase. Then measure the voltage on each electrode (pin) relative to ground. I presume the current is less than the PICaxe is able to drive comfortably?Ī Bridge is one way to generate a reversing current flow and you could put a resistor in series with each output pin. Also it's the current which needs to be measured, which can be done synchronously, i.e. IMHO it would be better to forget about "ac" and just consider the system as a (repeating) period of time divided into two "halves", when current flows in opposite directions to cancel electrolysis.
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