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'[PIC]: Homemade Programmer 16F877'
2001\01\27@060628 by Jeethu Rao

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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) ?

Regards,

Jeethu Rao

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2001\01\27@071701 by wzab

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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.
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                             Wojciech M. Zabolotny
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2001\01\27@111417 by Bob Ammerman

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You could add  a diode or two to the ground leg of the 7812 to bump its
output voltage up about 0.6 volts per diode.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\01\27@113019 by Dan Michaels

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Wojtek Zabolotny wrote:

>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.


This ckt is good. If you want to be able to adjust Vpp, use a
little potentiometer instead of the diodes, a .5-1K pot should
fine work with the 3K resistor shown.

Less safe would be to replace both 3K and diodes with a 5K pot
[less safe in that it is more easy to fry something in case where
the pot is adjusted to the wrong position].

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2001\01\27@115659 by Anand Dhuru

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Just break open the ground pin connection of the 7812 and put a diode in
series, cathode towards the circuit ground, anode towards the 7812 ground;
each such diode will raise the output of the 7812 by about 12V

Regards,

Anand.

{Original Message removed}

2001\01\27@123619 by Gary Chung

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Jeethu,
You can add a diode (IN4148) in between Pin 2 and the ground.
Your output will be 11.9V + 0.6V = 12.5V
Adding two diodes will further increase the 7812 output to 1.2V

Regards
Gary

DIY Electronics
Website : http://www.diyelectronics.com
Email      : .....Gary.ChungKILLspamspam@spam@diyelectronics.com


{Original Message removed}

2001\01\29@112051 by jamesnewton

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I count at least three simple 877 programmers at
http://www.piclist.com/techref/microchip/devprogs.htm

I hope you will contribute your programmer to the collection when you get it
working.

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jamesnewtonspamKILLspampiclist.com 1-619-652-0593
PIC/PICList FAQ: http://www.piclist.com or .org

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