On Sat, Jan 27, 2001 at 04:11:24PM +0530, Jeethu Rao wrote:
> Hi guys,
>
> My PIC Start Plus stopped working a week back and I decided to construct a home made programmer for programming 16f877s. I checked the PicList pages and I could not find a single schematic for a 16f877 programmer ! almost all the programmers were for 16F84.
>
> So, I decided to construct my own programmer. And I set out. I took David Tait's TOPIC as the reference design.
>
> TOPIC uses a LM 317 to get the high voltage (12 to 14 volts as Microchip says). I want to use a 7812  12 volts regulator instead of a 317.
>
> When I checked the output of a 7812 in an existing circuit with a DMM, it showed 11.9 volts.
>
> Now, my question to the experienced gentlemen on PicList is weather I can program a PIC using  11.9 volts for the VPP
> (Programming voltage) ?

I'd suggest connecting the 7812 in the following way:

                        +--------+
 > +16 (unstab.)        |        |           ca. +13.5 (stab.)
------+-----------------+  7812  +----+-----+----
      |                 |        |    |     |
    --+--               +----+---+    |   --+--
    --+--                    |        |   --+--
      |          +--|<|-|<|--+-+===+--+     |
     -+-         |  2 diodes    3k         -+-
            GND -+-

That way you get almost stable 13.5V. It should be much safer solution than
trying to program 16F877 with 11.9V.
--
                                  HTH & Regards
                              Wojciech M. Zabolotny
        http://www.ise.pw.edu.pl/~wzab  <--> wzab@ise.pw.edu.pl

http://www.freedos.org  Free DOS for free people!

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads