In message <018001c08850$1c770fe0$c79d56ca@swank>, Jeethu Rao
<jeethurao@CALTIGER.COM> writes
>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.

Try the P16PRO40, it accepts all the 'FLASH' programmable PIC's, the
circuit can be downloaded or you can buy it as a kit of bits with a PCB.
It works with my free software for all the FLASH chips. You can get it
from lots of different places, one is http://www.dontonics.com

>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

Personally I consider that a little too low, don't forget you lose a
little in the switching device. Add a silicon diode in the ground pin of
the 7812 to increase the voltage by about 0.7v. Most queries I get about
my software is down to insufficient Vpp voltage!. I always advise aiming
for 13v on the pin!.
--

Nigel.

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