Hi,

I am trying to design a PIC-programmable pwer supply. I'd like to select by
software any voltage between 1.5V and 15V. PCB space is VERY small.

So I decided to use a Dallas DS1804 8-pin programmable potentiometer managed
by a PIC 12C509 or similar to drive a LM317L (100mA is enough). The problem
here is that the DS 1804 can't stand more than 5V on ANY pin, including the
potentiometer pins. So, I can't use it to directly drive the LM317L.... It
follows that I have to use a transistor or FET to convert levels. While I
have no problems with digital circuits, I have little experience with Analog
ones, so I don't exactly how to do this.

My circuit so far is:

                                               +--------------+
                                               |              |    o 20V
     +-------+           +-------+ pote high   |              |    |
     |       | 3-wire    |     --|-------------|              |   +-----+
     |       |-----------|    /  |             |              |   |
|----0
     |       | interface |    \  | pote wiper  |              |   |LM317|
Out
     |       |-----------|    /<-|-------------|  "BLACK BOX" |   +-----+
     |       |           |    \  |             |              |      |Adj
     |       |-----------|    /  | pote low    |              |------+
     |       |           |     --|-------------|              |
     +-------+           +-------+             |              |
      12C509A              DS1804              |              |
                                               |              |
                                               +--------------+

Anyone can help me on what to put in the "BLACK BOX"?

Thank you in advance!

Regards,
Andres Tarzia
Tecnology Consultant, SMART S.A.
e-mail: atarzia@smart.com.ar