I no longer own a laptop with a parallel port, but I had one at one point BEFORE I made this particular version of the programmer. I also find the instructions very confusing. You have to disconnect power or the icsp cable when not in use, though, so as to avoid shorting power and ground. Why would you go behind your computer to turn your circuit on/off? I just add a switch to my breadboard/circuit to control Vdd. I have added a manual switch in some of my other progammers, but it never gets used. I don't like this, because then you can't run your pic from the programmer's power source. FYI, the original TAIT uses DB25 pin 4 to control Vdd. Because you double invert the Vpp line, you will leave it alone. :) Because you are buffering with the use of inverters, when you use a TAIT compatible programming softare, you will need to go into the programmer settings and invert the clock, data out, and data in. I still don't know what it's for, though. I also show the 10k pull down resistor that I omitted earlier. The collector connects to the 5k base resistor of the pnp transistor. The pnp base is already pulled up to Vpp. Collector does not attach to a pullup resistor. You should have another npn transistor to buffer the port from the potentially hazardous voltages at the pnp's base. Bonus points for anyone who can tell me why this is bad idea. At any rate, I have recklessly omitted this resistor. In addition, MCLR pin is an active sink of a few microamps. But that would be silly, since MCLR is usually going to be connected to an external pullup, anyway. I think it is to ensure that the PIC's MCLR pin does not float. The schemmy I used also showed a 10k resistor between collector and ground. When pin 5 of your parallel port goes low, it pulls the base low, via the 5k resistor. The 10k resistor keeps the base high - thus programming voltage off. Eventually, you will be connecting the emitter to 12.5V source. You can connect collector to Vpp pin, now, since it is close. Solder one end of your 5k (actually I used 3.3k cuz I had it lying around) to the base. Solder the 10k resistor between emitter and base. On my particular circuit, that's what I did, and it registers 4.24V as high, which should be enough.) Picture 2: The pnp transistor gets two base resistors wired as a divider. This makes the divider 2/10, which should still suffice. (Alternatively, you could just leave things the way they are, but connect Data Out transistor's collector to all remaining 5 10k pullups. I just realized that these two resistors will form a voltage divider, and if each is 10k data high will be 2.5V. Also, data out tranny should not be pulled up with the 10k resistor network. **EDIT: the base resistor for the "data in" tranny should be 22k. I messed up the pnp transistor in this pic. You need: A male DB25 socket 4x NPN transistors, such as the 2n3904 1x PNP transistor, such as the 2n3906 1x 7805 voltage regulator 1x LM317 voltage regulator (and appropriate resistors to make 12.5V) 1x 10k SIP resistor network 4x 10k resistors 1x 22k resistor* update for step 3 1x 5k resistor 1x 1k resistor* update for step 3 1x machined-pin chip socket soldering iron, protoboard, wraping wire, wrapping tool, glue gun. See step 7 for pics of the software I use and how to set up the programmer. These changes are already reflected in this list, but are not updated in all the pics. I had to add an additional npn transistor and change a couple of resistor values. :) There are a couple of changes, but everything worked out in the end. I have built several variations, and I thought I was on top of things. Click the smaller images below! ** This is a new variation and it didn't work 100% correctly on the first attempt. Best of all, it uses just two voltage regulator and 5 transistors! *** I added a pic of the final result, and pics of my new mini-programmer with a clear top. It is very reliable and there is good programming software available for free. This is a variation of David Tait's classic design. Make your own PIC programmer for your computer's parallel port.
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