Producing the PIC programming adapter

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Producing the PIC programming adapter

September 24, 2010, 11:30:44 am

I'm prepping the PIC programming adapter for a small test batch. It's still largely untested and unsupported, but it should be available to potential developers as is. I have used it to read the ID from a PIC 18F2550.

Here's the final partlist:
http://dangerousprototypes.com/docs/Bus ... ng_adapter

When I double-checked the boost converter values the Ct came out 2701pf instead of 270pf (55khz?) I've been using. I'm not sure if I got it wrong before, of if something is wrong now. I'll check by hand instead of using the design tool before finalizing the value.

Re: Producing the PIC programming adapter

Reply #1 – September 25, 2010, 01:11:06 pm

If you want, I can double check your calculations as well. Just PM me the numbers that you are using.

I'm dealing with some software and hardware failures on my 24F development board these days. Once I solve them, I'll try BP with the 24F256GB110 on board.

Re: Producing the PIC programming adapter

Reply #2 – September 25, 2010, 02:37:56 pm

That would be awesome, thanks!

I used this before:
http://www.nomad.ee/micros/mc34063a/index.shtml

With the values shown in the image capture attached. I used to get expected values for the Ct depending on the frequency, now it seems to be wrong. FOr example 470pf is the traditional cap for 43khz, but this calculator now gives 6302pF. I've been doing prototyping at 100khz with a ~240pf cap to keep the inductor small.

Quote

The circuit which was made this time used the 470-pF capacitor. In this case, it becomes ton=20ÂµS, toff=3ÂµS. Because it is, the frequency is f = 1/(ton+toff) = 43kHz. I used the value which is mentioned to the sample circuit of the data sheet as the value of the capacitor.

I'll do it by hand too, but it would be great to have an independent verification before producing the first 20 adapters.

Re: Producing the PIC programming adapter

Reply #3 – September 25, 2010, 02:52:25 pm

Here is a spreadsheet that I wrote to do some MC34063 calculations.

Re: Producing the PIC programming adapter

Reply #4 – September 25, 2010, 11:55:35 pm

I did some quick calculations by hand by using the formulas on the datasheet. Vf is 0 and Vsat is 1V in my calculations.

t_on/t_off is 2, (t_on+t_off) is 18 usec, t_off is 6 usec, t_on is 12 usec which makes Ct around 480 pF if I didn't do any mistakes in my calculations.

If I continue other calculations as well, I get I_pk 120 mA, R_sc is 2.5 ohm, L is 400 uH and C_o is 43 uF. I did minimal rounding while calculating these values.

Re: Producing the PIC programming adapter

Reply #5 – September 28, 2010, 01:07:37 pm

I got part way through the research on this, but ran out of time. One thing I noticed is that the Fairchild data sheet has absolutely no text or any hints about the capacitance. I guess you really need the Texas Instruments data sheet.

Re: Producing the PIC programming adapter

Reply #6 – September 28, 2010, 01:26:37 pm

Yes, the log charts are ok, but not particularly clear. I got hung up on that too.

Re: Producing the PIC programming adapter

Reply #7 – September 28, 2010, 02:00:03 pm

ON Semiconductor datasheet has good explanations, I used it for the calculations.

Re: Producing the PIC programming adapter

Reply #8 – October 05, 2010, 02:59:41 pm

Thanks for the help everyone. I ordered 20 of these today for developers.

Re: Producing the PIC programming adapter

Reply #9 – October 27, 2010, 01:00:27 pm

The adapter is now available at seeed for $7. This is intended for developers only, there is NO software support:

http://www.seeedstudio.com/depot/bus-pi ... Path=61_68

Re: Producing the PIC programming adapter

Reply #10 – October 27, 2010, 01:48:30 pm

It turned out very nice! I really like the stacking!

On my prototype I soldered a long .1" header and used a small cable to the BP.

Re: Producing the PIC programming adapter

Reply #11 – October 27, 2010, 03:27:46 pm

Is it ok that I order one to test and maybe try to program PIC's I have on hand or do you have determined a group of people to get them?

Re: Producing the PIC programming adapter

Reply #12 – October 27, 2010, 03:31:33 pm

They;re free to order, but there is currently no support. You might want to check out the piratePICprog code to make sure you would be able to add your PIC and compile it yourself. It's VERY rough right now. This is primarily to encourage a few programmers to buy them and maybe contribute some code

Re: Producing the PIC programming adapter

Reply #13 – October 27, 2010, 03:40:32 pm

Actually I would buy one to test it out and contribute to the project.

Just have to survive this week, then I'm free for some time.

Re: Producing the PIC programming adapter

Reply #14 – October 27, 2010, 03:48:59 pm

That would be fantastic, that's why I had them made