Hi

I've done something similar once, but I can't find the schematics right now,
but if you want me to, I will do a little digging in my archives.
Its a little dificult for me to see the details in your ascii drawing, so
maybe you could post a better drawing, and I might be able to help you

Best regards

Henrik Nowak
Infocom Electronics


> -----Original Message-----
> From: Andres Tarzia [SMTP:ATarzia@SMART.COM.AR]
> Sent: 22. juli 1999 14:51
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [OT] Help needed: PIC-programmable power supply
> Sensitivity:  Private
>
> 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