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Help with simple circuit/opamp project

Discussion in 'General Electronics Discussion' started by bears13, Feb 19, 2013.

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  1. bears13


    Feb 19, 2013
    I am working on a project in which I have to attach a hydrocarbon sensor to a microcontroller in order to read in the voltage and know if the sensor has detected something. I have attached the circuit for the hydrocarbon sensor. As you can see there are two resistors in parallel so the voltage will be constant. We need to figure out what supporting circuitry will be needed in order to read a voltage and amplify it so that our microcontroller can read it. We were thinking of connecting an opamp or two to amplify our signal, but we are not sure how to connect them to the sensor.
    We are really confused and need a good, easy-to-understand explanation. Any help would be appreciated.
  2. Laplace


    Apr 4, 2010
    Drive your sensor with a current source that will generate 5 volts to ground at the sensor's maximum resistance. 15 uA for 330 Kohm, 150 uA for 33 Kohm. Connect one end of the sensor to ground, the other end of the sensor to the current source & micro-controller analog input. You could place a 0.1 uF ceramic capacitor in parallel with the sensor to aid charging the internal S/H capacitor quickly. Construct the current source from a 9 to 12 volt power source, PNP transistor, emitter resistor, bias resistor and shunt voltage regulator such as the LM4041. The same regulated voltage can be used for both current sources.
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