🚀 go-pugleaf

I have an interesting Pulse Width Modulation design problem;

Given the following PWM waveforms:

  Minimum pulse width:

    <----------------- 18 mS ------------------->
    .--.                                        .--.
____|  |________________________________________|  |_____

  -->  <--
    1.0mS


  Maximum pulse width:
    <----------------- 18 mS ------------------->
    .----.                                      .----.
____|    |______________________________________|    |___

  -->    <-- 
    1.9mS

  The pulse width varies linearly with a transducer variance of
0 - 100%.  My question: is there a simple solution for the conversion
of this PWM signal into a corresponding analog signal, ie. a simple
circuit for the following black box?


             .----------.
   PWM in    |          |  Analog out
------------>|          |------------>
             |          |
             `----------'

where the analog output function looks like;


   Vcc  |                  .
        |               .
        |            .
        |         .  
        |      . 
        |   .
        |.
       -|-----------------,
        1.0              1.9

          Pulse Width (mSec)
           
  Obviously, if there exists a PWM De-modulator chip then this 
would be the answer, however I can find no such chip in any of
my Linear data books.  

  I currently have a solution using a oscillator, counter, and DAC
however, the chip count is higher than optimum (ie. one :-) ).


  Any suggestions would be appreciated.

    Darel.

-- 
Darel Mesher				...!uunet!mnetor!maccs!darel
McMaster University			    darel@maccs.mcmaster.ca