Post by thread:Programmer Power - Thanx for the Suggestions

Thanx for all the replies. Oh well, it seemed like a good idea at the time (is there a sheepish grin character?). Peter, 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? 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). myke {Quote hidden}>> >> Hi Folks, >> >> I want to develop my own Programmer (Everybody else is doing it), but I want >> to do a couple of things differently. >> >BIG Snip > >Myke. > Why not use an opto isolator to drive the Vpp pin the source current >of the driving diode is quite small and the speed of switching is more >than fast enough. It's what I used. As for the programming voltahe I >used a LM7812 regulator and placed a Diode in series with the Vref to >ground. this has the effect of raising the OP voltage to about 13.5 >volt. > > you can use the same trick for the 5 volt rail and a couple of >buffers/inverters for the programming lines. > > So there you have it 2 voltage regs,2 optos and one 7404. Your >programmer is complete. > > >Cheers Peter...... > >================================== >= New Ideas come from those who = >= didn't know it wasn't possible = >================================== > > 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

At 08:57 AM 11/25/96 EST, you wrote: {Quote hidden}>Thanx for all the replies. Oh well, it seemed like a good idea at the time >(is there a sheepish grin character?). > >Peter, > >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? > >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.) > Mike, 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 need one for the 5v Vdd, just use any GP PNP transistor and a single resister in the 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 arrangement 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! :-) Regards Jim -------------------------------------------------------- Jim Robertson NEWFOUND ELECTRONICS Email: spam_OUTnewfoundTakeThisOuTne.com.au http://www.labyrinth.net.au/~newfound PHOENIX Shareware Picstart 16B upgrade coming. For more details, send email to .....newfoundKILLspam@spam@ne.com.au with "subscribe phoenix mail list" in the BODY of the message. --------------------------------------------------------

myke predko wrote: {Quote hidden}> > Thanx for all the replies. Oh well, it seemed like a good idea at the time > (is there a sheepish grin character?). > > Peter, > > 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 > 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 = ==================================

Myke, > 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. Cheers, -- Martin Martin Nilsson http://www.sics.se/~mn/ Swedish Institute of Computer Science E-mail: mnKILLspamsics.se Box 1263, S-164 28 Kista Fax: +46-8-751-7230 Sweden Tel: +46-8-752-1574