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'Programmer Power - Thanx for the Suggestions'
1996\11\25@085830 by myke predko

Thanx for all the replies.  Oh well, it seemed like a good idea at the time
(is there a sheepish grin character?).


I think I would go with your suggestion.  I presume the circuit would be:

+15V-----+----------| 7812 |-----+--------------------+      +--- To Pwr
         |          |______|     |                    |      |    Control
        ---Filter       |       ---Filter              \|    -
        ---Cap          -       ---Cat                  |    ^
         |              ^Diode   |                     /|    |
         |              |        |                    |      |
         +--------------+--------+                    |      +--- To +5V
                        |                          To PIC
                       Gnd                         to be

For the Programming Voltage?

Also, thanx for the suggestion about doing +5V as well (I forgot about
that).  I already have a 7805 in the Circuit, so adding this won't be a
problem.  (Just an opto-isolator in this case.)

Just out of curiosity,

Again, thanx to Antti, Martin, and Hank for pointing out that my circuit
wouldn't work for 16C61s, and 16C71s (which is really what I wanted it for
rather than just the 16C84).


{Quote hidden}

Today, the commercial sector is advancing computer and communication
technology at a breakneck pace.  In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).

Aviation Week and Space Technology, October 28, 1996

1996\11\25@094418 by Jim Robertson

At 08:57 AM 11/25/96 EST, you wrote:
{Quote hidden}


You need at least one more diode in the common pin of the 7812. I use two but
I noticed Robin Abbott goes with Three. Either will put you in range but just
one diode is a little low.

I think using an opto coupler is a little extravagant. You certainly don't
one for the 5v Vdd, just use any GP PNP transistor and a single resister in
base line. (High = off and low = on.)

For the 13V Vpp, you need to do some level shifting. An opto coupler
can do that but I think a PNP transistor switched by a common emitter NPN
transistor is a cheaper alternative. You will need 3 resisters, 2 in each base
line and one on the collector-base junction of the PNP "series pass" switch.

You can also use two NPN transistors and a zener diode reference. configure
the first NPN as a common collector with 14V worth of zener/led/diode drop
on the base
and a pullup to unreg 16V. This will give 13.4 volts out on the emitter. To
turn it off, the second (common emitter) NPN is biased on and its collector
pulls the base
of Q1 to ground thus turning Vpp off.

This is how the parallax programmer does it. You will also see the same
shortly when the postman comes. Feel free to copy me because I copied it from
parallax already. :-)

Sorry I have not done any diagrams but at  1:45AM and, for nothing, forget
it! :-)



Jim Robertson

PHOENIX Shareware Picstart 16B upgrade coming.
For more details, send email to with
"subscribe phoenix mail list" in the BODY of the message.

1996\11\25@134532 by efoc

myke predko wrote:
{Quote hidden}

That looks like it but might i suggest a pull down on the open end of
the opto to pull it back to GND when it is not switched on. It will just
float otherwise and not return to GND. I used a value of 10K for mine.

Peter ........

= New Ideas come from those who  =
= didn't know it wasn't possible =

1996\11\27@085055 by Martin Nilsson

picon face

> I think I would go with your suggestion.  I presume the circuit would be:
>                       ______
>  +15V-----+----------| 7812 |-----+--------------------+      +--- To Pwr
>           |          |______|     |                    |      |    Control
>          ---Filter       |       ---Filter              \|    -
>          ---Cap          -       ---Cat                  |    ^
>           |              ^Diode   |                     /|    |
>           |              |        |                    |      |
>           +--------------+--------+                    |      +--- To +5V
>                          |                          To PIC
>                         Gnd                         to be
>                                                   Programmed
> For the Programming Voltage?

It seems you placed the diode upside-down in your diagram. If you use
several diodes in the bias path of a series regulator, remember they
reduce stability.

I wouldn't recommend using an optoisolator this way. It may work, but
you will have problems staying within specs. The C84 requires a Vpp
rise time of 1us. Optoisolators which have such short rise times are
usually for lower voltages and rarely accept 12V Vce. Also, they have low
CTR (current transmission ratio), which means you have to send a lot
of current through the primary side to get anything out of the
secondary side. For non-C84 PICs with higher Ipp, the current limit
for the diode might be exceeded.

The rise time is something to keep in mind. I know a report of
problems with the AN-589 due to slow switching. (The programmer ended
up programming from location 1 instead of 0.) I agree with Jim's
suggestion of going with PNP transistors, but even there you have to
be careful.


-- Martin

Martin Nilsson                 
Swedish Institute of Computer Science    E-mail:
Box 1263, S-164 28 Kista                 Fax: +46-8-751-7230
Sweden                                   Tel: +46-8-752-1574

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