How do I convert voltage from 0 to 5V into -10 to 10V

Discussion in 'General Electronics Chat' started by kevin.cheung19, Nov 28, 2011.

  1. kevin.cheung19

    Thread Starter New Member

    Nov 22, 2011
    24
    0
    I want to use a microcontroller to control a motor. The output voltage that I can control from microcontroller is 0-5V, but I need to be able to input -10V to 10V analog input to the motor controller to control the speed of the motor. Is there any chip that can map a 0-5V signal into a -10V to 10V signal. I can supply a +15V and a -15V supply.

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I did almost the identical circuit for someone else awhile back.

    See the attached.
     
    kevin.cheung19 likes this.
  3. kevin.cheung19

    Thread Starter New Member

    Nov 22, 2011
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    0
    This is awesome! But I was wondering is there any pre-built IC chip that I can use here? If not, then I can build the circuit myself
     
  4. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    SgtWookie,

    Very nice circtuit, and exactly what he needed. For anyone interested, the transfer function for his circuit is: Vout = 4Vin - 10

    Try plugging in 0-5V for Vin and you'll get the same numbers that his graph shows.

    One small idea to simplify the circuit ... For a non-critical application like this, why not make the 5V reference voltage with a simple voltage divider? You can increase the op-amp feedback resistors to 100K and then use 1K resistors for the voltage divider with minimal error. Resistors cost less and take up less room than a 5V linear regulator.
     
  5. tgil

    New Member

    May 18, 2011
    19
    4
    Try looking at the Si9986 from Vishay. I have used this before for motor control using a microcontroller. You will need to use a pulse width modulated signal to control the motor speed. The overall setup is very simple. You just need the MCU, the IC, and two power supplies. A 5V supply for the MCU and a 10V supply for the motor. The H-bridge takes care of the -10V.

    Good Luck
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    In a prior iteration, I'd used a pair of 20k resistors with a 10v source; this worked out to have minimal errors.

    I like to present circuits that have very close (if not exactly) to what the inquiring member needed, in a hopefully easy-to-understand manner.

    The circuit I presented does have some minor errors due to the input offsets of the two opamp channels; the left opamp would have its' input multiplied by four, the right opamp by two - and the errors are cumulative. The total error in this circuit would be somewhere around 16mV, and that will change depending on the accuracy of the 78L05; as it's error will also be multiplied.

    I suppose one might use a couple of 1k resistors - or a 2k pot to provide adjustment. I like to keep resistive dividers having somewhere between 100uA and 2mA current; I more or less automatically discard values above 2mA due to excessive current. 6mA certainly would not be excessive in this case, as the idle current of a 78L05 is about that anyway.
     
  7. AdrianN

    Active Member

    Apr 27, 2009
    97
    1
    This is a unipolar to bipolar converter. It can be done with one op amp. You can use a differential amplifier to design it. Use this calculator to find the resistor values.

    http://masteringelectronicsdesign.com/differential-amplifier-calculator-2/

    Also, this article gives you step by step instructions on how to design a unipolar to bipolar converter:

    http://masteringelectronicsdesign.c...-converter-for-a-unipolar-voltage-output-dac/
     
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