*** I added a pic of the final result, and pics of my new mini-programmer with a clear top. Click the smaller images below!
** This is a new variation and it didn't work 100% correctly on the first attempt. I guess I got ahead of myself.. I have built several variations, and I thought I was on top of things. :) There are a couple of changes, but everything worked out in the end. I had to add an additional npn transistor and change a couple of resistor values. These changes are already reflected in this list, but are not updated in all the pics. See step 7 for pics of the software I use and how to set up the programmer.
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.
Step 1: Index Card
Then bend the legs of the SIP resistor network, and glue as shown.
Step 2: ICSP Port
Now glue port down.
Now is also a good time to glue your transistors on. You can also solder the emitter of your npn transistors to the ground plane, now. I have labelled each transistors purpose here.
The three npn transistors will be wired as inverters. They will essentially "take power away" from their respective pullup resistor when a current is placed onto their base pin.
The PNP transistor (upside down) will control the programming voltage. It is also going to invert it's signal.
**EDIT: I just realized an omission in this design. There should be one additional npn transistor that is used to drive the PNP transistor. This will buffer your computer port from the voltages at the pnp's base. My bad. This will also uninvert the signal. See step 8.
Step 3: Base Resistors
**EDIT: the base resistor for the "data in" tranny should be 22k. Also, data out tranny should not be pulled up with the 10k resistor network. Instead, pull it up with a 1k resistor. I just realized that these two resistors will form a voltage divider, and if each is 10k data high will be 2.5V... no good. (Alternatively, you could just leave things the way they are, but connect Data Out transistor's collector to all remaining 5 10k pullups. This makes the divider 2/10, which should still suffice. On my particular circuit, that's what I did, and it registers 4.24V as high, which should be enough.)
The pnp transistor gets two base resistors wired as a divider. Solder the 10k resistor between emitter and base. Solder one end of your 5k (actually I used 3.3k cuz I had it lying around) to the base. You can connect collector to Vpp pin, now, since it is close.
Eventually, you will be connecting the emitter to 12.5V source. The 10k resistor keeps the base high - thus programming voltage off. When pin 5 of your parallel port goes low, it pulls the base low, via the 5k resistor.
The schemmy I used also showed a 10k resistor between collector and ground. I'm not sure what it's for. I think it is to ensure that the PIC's MCLR pin does not float. But that would be silly, since MCLR is usually going to be connected to an external pullup, anyway. In addition, MCLR pin is an active sink of a few microamps. It doesn't float. At any rate, I have recklessly omitted this resistor. Bonus points for anyone who can tell me why this is bad idea.
Step 4: DB25 Port
You may glue it on the edge of the card, for now.
No wait! You glued it too soon! First make pins 18-25 common, as they will be common ground pins. Oh.. it's ok, cuz the card can bend.
Actually, a better way to do this part is to bend each pin over onto it's neighbor, then solder them down. I am just trying to illustrate how the connections should go.
Step 5: DB 25 Connections
Pin 3 is the clock out pin. Connect it to the "clock out" base resistor.
Picture 2: pin 10 is the data IN pin. Connect this to the pullup resistor of the "data in" transistor, as seen in blue circles.
Pin 5 is the programming voltage pin, or Vpp pin. See step 8. You will need to add a fourth npn transistor, and connect this line to it's base resistor. The transistor's collector will connect to the 5k base resistor of the pnp transistor. The emitter will connect to ground plane.
Step 6: ICSP Port Side
The ICSP data pin will connect to BOTH the pullup resistor for the "data out" tranny AND to the base resistor of the "data in" tranny. BLUE circles **EDIT: pull up Data Out with either a 1k resistor, or with all 5 remaining 10k pullups on the resistor network. Using just one 10k resistor will cause data high signal to be divided down to 2.5V.. That won't register as high, as CMOS parts running at 5V need about 3.5V to register high.
The Vpp pin will connect to the PNP transistor's collector.
The Vdd pin will connect with your network resistor pin 1. ORANGE circles If you want an on/off switch on the programmer, insert it between these points.
The ground pin will connect somewhere on the ground strip.
The clock pin will connect with the pullup resistor of the "clock out" transistor. YELLOW circles
Step 7: New Pictures... Finished and Tested.
I pulled out my LCD for a quick test. It reads, writes, erases. What more can you ask? Check the pics for a screenshot of how to set up ICProg or PICPgm programming softwares. Also check step 8 for detail of a couple of corrective measures that are featured here.
I added two lm317's for 5V and programming voltage.
Step 8: Correction!!!
You should have another npn transistor to buffer the port from the potentially hazardous voltages at the pnp's base. This is depicted in the top left. Collector does not attach to a pullup resistor. The pnp base is already pulled up to Vpp. Emitter is grounded. The collector connects to the 5k base resistor of the pnp transistor. I also show the 10k pull down resistor that I omitted earlier. I still don't know what it's for, though. :)
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. Because you double invert the Vpp line, you will leave it alone.
FYI, the original TAIT uses DB25 pin 4 to control Vdd. I don't like this, because then you can't run your pic from the programmer's power source. I have added a manual switch in some of my other progammers, but it never gets used. 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. You have to disconnect power or the icsp cable when not in use, though, so as to avoid shorting power and ground.
Step 9: Schemmy, Using a 9V Battery! and a Gratuitous Kitty Photo :)
OR you could leave the 9V battery connected to the pnp transistor, but disconnect it from the 7805. Then insert your external power source, less than 35V, to the 7805. Well, now that you understand how the programmer works (ya do, right?), you can modify it any way you like from here. Adding some indicator LEDs might be nice?
Pic 2: Smurfy. Shhhh, she's sleeping.