Last one...I mean it

[GatorGnet]

At least for this weekend. While waiting on things to arrive in the mail, I took another stab at a simple JDM inspired programmer. This time I added the 12 to MCLR for those serial ports that aren't doing it. I will take whatever feedback you can give.

**broken link removed**

 

[Pommie]

On this page you will find this diagram for an improved JDM programmer. The BAT42 diodes aren't necessary.

**broken link removed**

Mike.

 

[GatorGnet]

That is what I was after. What is the benefit of going from TxD to a NPN then to a PNP to MCLR?

Would the one I sketched work?

 

[ericgibbs]

That is what I was after. What is the benefit of going from TxD to a NPN then to a PNP to MCLR?

Would the one I sketched work?

No,

You cannot put 12V into a 12Vreg and get 12V out..

 

[skyhawk]

That is what I was after. What is the benefit of going from TxD to a NPN then to a PNP to MCLR?

Would the one I sketched work?

In order to turn on an NPN transistor, the base must be about .7V above the emitter. Or put another way the emitter is .7v below the base. In your circuit the maximum possible potential for the base is the maximum for TxD, the maximum potential at the emiter will be .7V less than that.

Rule of Thumb: Use PNP transistors for high side switching and NPN transistors for low side switching.

 

[colin55]

You actually need more than 12v Vpp to turn on some chips.

I designed a lot of programmers and you need 13v to 13.5v to guarantee some chips turning into programming mode.
Other than that I have programmed thousands of chips with JDM-type programmers.
All chips program the first time but some F628's won't reprogram as they get "locked up."
Other times they take 6 "goes" to reprogram.

 

[skyhawk]

If you've got 4 NPN transistors, 1 PNP transistor, and 5V and a 12V regulators in your parts box you might want to look at this Tait style programmer, while you wait for your parts order to arrive.

5 transistor PIC programmer *Schematic added to step 9!

The implementation there is ugly, but the circuit should work. Build it on a breadboard instead.

You can boost the output of a 12V regulator by putting one or 2 diodes in the ground leg. The input to a 78xx needs to be at least 2.5V higher than the desired output. I've found a cheap 12V ac wall wart will produce 19-20V when rectified, filtered and run with a light load. I've obtained similar results with an unregulated 12V wall wart. YMMV!

 

[GatorGnet]

Thank you everyone for the great help. It may seem like it but I'm not trying to cut corners only learn the who what and why things are done. I'll end up building a PicKit 2 but I wanted to try some others too for more practice and learning experience.

What if I just put the 12v wall wart directly to the Vpp? Since TxD turns on the Vpp and Vdd at the same time, can Vpp be on at all times during read/write operations? Or do they have to be applied at the same time?

Colins55, I hear you on that one. I can't remember what chips I use to use but since I switched to the 628a's they wont program on a standard JDM.

 

[colin55]

To convert previous versions of Programmers:
Cut the track connecting pin 10 to 5v rail.
Fit a 10k resistor between pin 10 and 0v rail.

The PIC16F628A has some different features to the PIC16F628 and cannot be programmed on the old version of IC PROG (version v105c). The new version is called (v105c-a) **broken link removed**.

 

[GatorGnet]

Holly Crap! I tried the 105c-a version and my JDM worked! I tried all different software builds and none of them worked but this. Well this will allow me to at least finish what I have been working on...!!!!!!!!!!!!

Was there something changed in V106? I have been trying it and it hasn't been working.