Fluid level meter version 2


Posted on Feb 5, 2014

IC4 is a counter/oscillator combination and is the key element in the circuit. The oscillator outputs its AC signal on pin 7. This signal is lead (through voltage divider R3/R4) to pin 3 of IC5 (multiplexer IC) which is used as an input. The same signal is also lead to the rectifier/demodulator build up with D1/R1/R5. The resulting rectified signal is compared (with IC2, an opamp) with a constant voltage. If a selected electrode is under water, there will be an extra load on the AC signal, which causes the output of the demodulator to drop a little bit. The comparator will react by changing its output level. All this takes a fraction of a second because the multiplexer will only handle one electrode at a time by connecting the AC signal to the selected electrode.


Fluid level meter version 2
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