Mesure sensor voltage by 328p and OP Amp in parallel

I am designing a circuit to measure the temperature via a thermistor via the ADC pin on a 328p and I am looking for some advice. As a failover I am also using an OP Amp as a comparator, to see whether the voltage exceeds a certain threshold. My question is the following. What can I do to protect the analog voltage line of the thermistor from interferences from the 328p? Can I connect the thermistor out directly to the 328p and to the MCU? My ideas are the following:

  • Using an in-line diode before the 328P adc pin, so that it can measure voltage but not interfere with it.
  • Using an OP Amp voltage follower to provide the voltage to the 328p pin

Is there a better way to do so? Are my possibilities feasible or are there any problems? What are the advantages and disadvantages of one or the other solution?

I am thankful for any help or advice.


Why would it be necessary to protect your thermistor from the 328P? As long as the connected ADC pin on the 328P remains configured as an input, there's no reason to assume that the 328P will interfere with the thermistor in any significant way. Or is there crucial information on how you intend to use the 328P that may bring particular safety concerns?

Having said that: idea 2 would be superior to idea 1 IMO due to the inevitable voltage drop across D1 in idea 1.

This looks like a school project. I would use idea1 without the diode but a 10K resistor replacing it incase you get transients in the sensor line.

The 328p is used to switch a relay while taking safety mesures (temperature, smoke,...). There is a analog safety circuit (comparators etc). Si I am afraid if, for any reason, the 328p locks up or is buggy, it may interfere with the voltage mesure lines...

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