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about voltage follower op amp

Discussion in 'General Electronics Discussion' started by yougarage, Aug 5, 2011.

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  1. yougarage


    Jul 13, 2011
    I'm going to "read" an analog signal with arduino, an ntc temperature sensor.
    The analog input pin has a very high impedance.
    If I connect the ntc directly to the pin everything works fine.
    Can I have any benefit if I interpose a voltage follower between the sensor and the arduino pin?
    I'm a novice so I don't know if this reasoning is right:
    If the sensor cable is short and the environment is quiet I don't need a buffer (voltage follower)
    If the sensor cable is long and / or the environment is noisy I should put the buffer very close to the sensor, and send the op amp output to the analog pin.
    Are these statements right?
  2. duke37


    Jan 9, 2011
    If it is working OK then adding an op-amp will not help, don't complicate matters if it is not necessary.
    The sensor will have a low output impedance, lowering this further with an op-amp near the sensor will make little difference.
    The temperature sensor will not be able to respond to very fast temperature changes so, if there is noise picked up by the cable then high frequency interference can be reduced with a resistor in series with the feed and a capacitor across the arduino input.
    Use a shielded cable to reduce interference.
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