Switch mode power supplies do not generally provide isolation. You have to use a topology, usually with a transformer, that does provide isolation. If there is significant capacitance from the circuit common to "earth", you will have major problems. For this kind of application, you really need to have it battery powered so that it is genuinely isolated.
Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net
Jim very sorry,
What i meant to say was that i will have an analogue switch , was an error say smpt.
Yes it is battery powered.
My switch will be SN74LVC1G66
Once again sorry for the error
What is the function of that "switch" and what drives it? The output of an MCU is just as good.
As its analogue switch it will isolate the probe connectors and the known resistance.
This way only one of them will be getting the outputted square that will be feed into the op amp.
But yes i agree that i could have two separate GPIO pins outputting a pulse 1. to Connector 2. resistor, both then feeding to the op amp.
It just accord to me that any GPIO can be used as i no longer using a PWM dedicated pin.
Again, if you don't have exactly (or very near so) 50% duty cycle, you will destroy your sensor. Maybe adding some capacitive coupling in the drive would be helpful--that ensures no DC component (assuming good low leakage cap).
In direct drive methods, sometimes an integrator is used (as a feedback ) to force the DC average to zero.
When in the dark remember-the future looks brighter than ever.
Will keep it 50% duty cycle ,
how would it destroy the senor? I will be using steel probes.
Yes I will be adding coupling cap on pins that is outputting the wave. Is there away to calculate best value for my applications?
The sensor cannot tolerate DC, so an exact 50% (perfect balance) is required. Also, if you add caps, then that wave will curve itself to enforce a zero dc condition.
Yes my signal is 50%. I have made sure with the timer/counter.
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