D. R. Chicotel wrote:
>
> I have a PIC that is producing a serial data stream that I want to
> superimpose on a constant DC source such that a 0 bit is 12V and a 1 bit is
> 17V.  The DC source is provided by a LM338 which is a three pin adjustable
> voltage regulator.  I want to connect an output pin from the PIC to the
> reference pin on the LM338 in some way, but I have no idea what would be the
> correct way to do this.
>
> A related question:
>
> How would you extract the logic level voltage from this DC source just
> described so that another PIC could read the data stream?  A zener diode
 maybe?
>
> I am trying to provide power to a motor and serial commands to a PIC using
> the same two
> wires.  The PIC would sit between the motor and the power and issue the
> appropriate PWM signals to the motor as directed by the data stream.
>
> Does anyone have any ideas please?
>
> Thanks - DRC
You could clean up the edges of your signal if you use a shcmitt trigger
opamp configuration.Or consider impressing a frequency shift key signal
on the 12v line.If you use a voltage divider on lm338 simply pull it up
with a diode from the pic output. my 2 cents. Tony M.