Bipolar input to two unipolar outputs

Discussion in 'The Projects Forum' started by sotkoon, Oct 5, 2012.

  1. sotkoon

    Thread Starter New Member

    Sep 24, 2012
    Hi all,

    I am in a robotics project that requires control of DC brushed motor. I have a controller box that output one bipolar control signal to tell the motor how much to turn.

    I would like to turn this signal into two unipolar signal as described in the picture below, so that it can be fed into MCU to turn into PWM signal, before sending it to PWM motor driver (Pololu DRV8833) to drive the motor.

    Any experts can point me the direction/reference on what I should be looking at? I am aware that there is this summing amplifier technique to raise the voltage level into unipolar signal.

    Your kind assistance will be much appreciated. Also, please let me know if my description is not clear.

  2. bertus


    Apr 5, 2008

    You could go the following route:
    Attenuate the input signal ( you will have +5 and -5 Volts )>
    Add 5 Volts ( you will have +10 and 0 Volts )>
    Invert this signal ( you will have the 0 and +10 Volts ).

    I have made a simple circuit that will do the trick, in an other way:


    The used chip is an 40106.
    It will need buffering, when high current loads are used.

    Last edited: Oct 5, 2012
  3. DickCappels


    Aug 21, 2008
    That's a pretty clever circuit.

    Bertus, I am pretty sure that your circuit will work with a 10V power supply if a CD4000 or CD4500 series part is used, but in that case, would the resistor values have to be different?

    Is there some concern about enough current getting through the 2k resistor to cause SCR latchup?
  4. bertus


    Apr 5, 2008

    The 4000 series will work between 3 and 15 Volts.
    You can take higher values for the resistors, as long as the ratio is the same.
    You can not make them to high as the input current of the ports will influence the circuit.
    I do not know where the +10 / - 10 Volts signal comes from.

    I see I made a mistake as the output of the voltage divider / adder will change between 0 and 5 Volts.
    The 40106 will probably not switch on those voltages when powered with 10 Volts.

    When you change the 1K resistor to 10K and leave the others 2K, the voltage will change from 0 to 9 Volts.
    The 40106 will switch on that when powered with 10 Volts

    Last edited: Oct 5, 2012