converting duty cycle to voltage signal

Discussion in 'The Projects Forum' started by RotatingEmu, Sep 8, 2009.

  1. RotatingEmu

    Thread Starter Member

    Jun 15, 2007
    11
    0
    Hi I was wondering if anyone would have some advice for the following problem:

    I have 4 PWM signals that I want to convert to analog voltage signals.

    I realise I can use a simple LP filter to change the PWM signal into a voltage,

    the only problem is that the Peak to Peak of the 4 PWM signals is slightly different (but ideally should be the same).

    However, the duty cycle of each PWM is very accurate so I would like to find a way to convert the duty cycle of each PWM into a 0.7 to 5V signal.


    Could I use a transistor as a switch (or somesort of electronic switch), to get consistent p-p PWM signals, then just use a LP filter?

    Any suggestions would be appreciated.


    Thanks
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    What is the level of the existing PWM signals? Is it above the 5 volt level? If so, you could use 5 volt zeners with limiting resistors to limit the voltage to 5V/0V levels and use the LP filter to develop the variable voltage.
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Pass the PWM signals through a buffer and you will then have isolation, buffering and exactly equal output PWM signal level.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    The buffer idea is good, like using a CMOS hex buffer IC.

    But this might be simpler; instead of just using a RC lowpass filter, use a RC+R where the 2 resistors form a voltage divider. If you make one of the resistors a trimpot you can adjust the DC output voltage to calibrate it.

    At the very simplest level you only need 4 trimpot and 4 caps, but you probably will want finer calibration control so that's 4R 4C 4trim etc.
     
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