Read 4-20mA, output 0-5VDC t0 MCU Ain

Discussion in 'The Projects Forum' started by MCUman, May 15, 2007.

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  1. MCUman

    Thread Starter New Member

    Apr 4, 2007

    I am trying to read the pressure sensor output which is a 2-wire 24vdc powered loop and convert it to 0-5Volts for a MCU to read into its ADC circuit.

    I have experimented with the simple series Voltage Drop (ie 1% accuracy type). The output varies quite a lot. The accuracy is not acceptable.

    The ic RCV420 has also been ruled out due to cost, delivery factor, dual PSU rail +ve -ve issue(spell: cost).

    Any other cheap and accurate way?

    -Mcuman (1st post)
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    A 100 ohm resistor should do nicely as a curent-to-voltage converter. 4 mills current will be 40 mv, and the 20 mills will become 2 volts. A op amp with the output trimmed to zero for the 40 mv input, and with the gain adjusted for 5 volts for the 20 ma limit should do the trick for you A to D input.
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