polarity detection circuit

Discussion in 'The Projects Forum' started by nobody102, Aug 29, 2010.

  1. nobody102

    Thread Starter New Member

    Dec 27, 2009
    3
    0
    I am trying to re-purpose an RC/remote control to interface to an Atmel AVR MCU. The existing output of the R/C receiver drives a small DC motor with +/- 3 volts on two wires out. The motor will be discarded. This corresponds to pressing one of two switches on the transmitter. Let's call them S1 and S2. When S1 is pressed, the receiver outputs 0,+3V. When S2 is pressed, the receiver outputs 0,-3V, i.e. the polarity on the two outputs is reversed. I need a simple/cheap cicruit that can detect the polarity and drive two mutually exclusive outputs (A,B) to Vcc. When no switch is pressed (0 volts out on the R/C), both should be low. When +3v is present, A goes high.
    WHen -3 volts is pressed, B goes high. I am thinking I need some kind of comparator, did some googling for "polarity detection circuit" and have not had much success. Any suggestions would be appreciated!

    Thanks,
    Leor
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    If common grounding isn't necesssary just feed the output through a bridge rectifier then you'll always have 0 - 3V regardless of the button pressed. Use that to drive a small reed relay or some other sort of creative output circuit.
     
  3. nobody102

    Thread Starter New Member

    Dec 27, 2009
    3
    0
    Thanks. However, I need to distinguish between the two voltage states, not take the absolute value of them.
     
  4. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    Does the 2nd output ever go to zero? If not, you can just put a diode in series which will output ~2.3V (a logic high on CMOS 3.3V) when forwards and 0V or so in any other state.
     
  5. nobody102

    Thread Starter New Member

    Dec 27, 2009
    3
    0
    Thanks. I will play around with some diodes.
     
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