Because the joystick port requires a variable resistance rather than a
voltage this isn't overly simple.  A digital pot is the easiest way as you
have already found.

You could use the PIC's PWM, (low pass filitered) to drive a FET which will
operate as a crude voltage controlled resistor.  Linearity should be
reasonable, but it will have a fairly high temperature coefficient.  Take a
look at http://www.vishay.com/document/70598/70598.pdf for lots of
information on using FET's as voltage controlled resistors.

Regards

Mike

> -----Original Message-----
> From: BBJ [SMTP:bbj@plz.co.za]
> Sent: Friday, May 10, 2002 6:02 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [pic]: Analog values using PWM
>
> I have an application that uses the joystick ports on a pic to read values
> on 4 20K pots.
>
> apart form using digital pots, which i may very well have to use, how can
> i
> simulate the pot values with a PIC ( some PWM ?? ) ??
>
> Accuracy is not THAT important, as i think the  A/D on the joystick port
> isnt all that acurate anyway.  I do however need decent linearity.
>
> The end result is a pic will receive a signal via rs485 that it must then
> "send" to the joystick ports. I dont have access to the original pc side
> program to change the way it works.
>
> Any ideas???
>
> John
>
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