AVR-Chat

--- In AVR-Chat@yahoogroups.com, Ralph Hilton <ralph@r...> wrote:

> I would be inclined to use an analog switch such an a 4053 and the 
ADC. Take a resistor
> from Vcc to an ADC pin. Connect the control of the 4053 to a high 
frequency signal. The
> pins ADC in and GND would connect to the switch which would reverse 
the output polarity at
> the frequency of the control signal. The 2 output lines then 
connect to the water
> container via small caps. The ADC pin would need a smoothing cap. 
thus the ADC would see
> an easily measured DC value but the probe would see AC.

Seems unnecessarily complicated to me. Why not use a (AVR generated) 
square wave signal capacitor coupled to the probes and measure the 
current thru a sense resistor just in the halfwave with the right 
polarity? Or - if really necessary spend some cents on an opamp which 
does precision rectifying (and amplification while we're on it) of 
the voltage across the current sense resistor.

Just my 2c,
Stefan