>
>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
>

>In message <199701291619.KAA07644KILLspamhouinet1.hou.moc.com>, "D. R. Chicotel" write
>s:
>>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.
>
>        The LM338 adjust pin is a good place to start.  The usual
>configuration is to have a resistor leading from the adjust pin to ground.
>The value will be somewhere in the 2-5 K-ohm range to allow you to get 12
>Volts out.  There is also a 250-ohm resistor which acts as a feedback from
>the regulated output (case) to Adjust.
>
>If you are feeding more than 17 volts in to the un-regulated side of the
>LM338, you can put a fixed resistor between Adjust and ground to set 17
>Volts.  Call this R1.  Take a second resistor which we will call R2 and
>choose its value so that when paralleled with R1 the output of the 338 drops
>to 12 Volts.  This is your modulation input.  Instead of grounding R2,
>connect it to the open-collector (or drain) output of the PIC.
>
>        In the high state, R2 just won't be there and the output should be
>17 Volts.  In the low state, R2 is paralleled with R1 and should give you
>12 Volts.
>
>        The LM338 has some protection circuits which are supposed to detect
>thermal and over-current overloads so I don't know how fast you can modulate
>without causing strange things to start happening.  I don't even know if
>it is an issue, but keep it in mind.  Also, if the PIC output can not handle
>the current or voltage involved, one might need to add a transistor and
>connect R2 to the collector of that instead of directly to the PIC.
>
>

>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