Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
22 Feb 2008 6:46 PicKit 2 FULL with TH components - Need help with layout
Greetings All,
I drew the original schematic for the PicKit 2 into Eagle using all through-hole components. I substituted the dual MOSFET with discrites, and replaced the op-amp with a through hole version. All of the other parts are identical to the original (just through-hole).
The problem is when I built the circuit, the device connects and is recognized by both MPLAB and PicKit software, but it disconnects randomly, the PicKit software detects either a short in Vdd, or Vdd=0V. Sometimes it reads correctly. Vpp is all over the place. Again, sometimes it reads correctly. When I test it with my meter, everything reads correctly. MCLR on/off works properly. 30kHz toggle works properly on both the PGC and PGD pins. I am also able to store a unit ID, but it will not calibrate. Vdd reads 4.26V on my meter.
I am pretty sure the schematic is correct. Maybe the MOSFET's and/or op-amp are too slow? I think it is the layout. The only way to keep it single-sided was to add several jumper wires and I think that added too much capacitance.
I am relatively new to designing PCB layouts. I dealt mainly with perfboard (hobbyist style). If somebody more experienced than I in designing layouts could assist me I would be most grateful. I will post my Eagle files. Thanks.
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Joined: 08 Jun 2004 Posts: 324 Helped: 51 Location: Sao Paulo - Brasil
22 Feb 2008 22:02 Re: PicKit 2 FULL with TH components - Need help with layout
Hi !
I could not see the files you posted, but I wonder what are the through hole discretes replacement mosfets you used instead of smd parts (I tried to find some mosfets with the same specifications of the mosfets used in the PICKIT2 original circuit, but I was not well succeded).
Returning to your problem: maybe your USB port cannot supply enough current to your PICKIT2 circuit. Have you used the decoupling 100nF capacitors near the supplying pins of the 18F2550 ?
Are the replaced mosfets electrically equivalent to the original mosfets ?
I think long wire jumps will not harm the functioning of the circuit (but i couldnīt see the layout).
23 Feb 2008 13:51 Re: PicKit 2 FULL with TH components - Need help with layout
Please check for proper polarity of pins of the MOSFETs used. while soldering some reversals possible. ensue this aspect
I could do the crosscheck of layout and the schematic if you could mail me directly at mvs_sarma(at)yahoo.com
oops! I may not have Eagle, but i will try to load it
Added after 1 hours 59 minutes:
Computerman29 wrote:
OOPS!!! I forgot. Thanks.
I soldered a 100nF 0805 between power pins on the bottom of board. It now passes all tests, but it still won't calibrate.
The software reads Vdd= 4.1v Vpp=Vdd on 3v devices and Vdd= 4.5v Vpp=11.9v on 5v devices.
My meter reads Vdd=4.23v Vpp=Vdd on 3v devices and Vdd=4.61v Vpp=12.04v on 5v devices.
Vdd seems a bit high for 3v devices, but the software says it passes.
BTW, the MOSFET's are ON Semiconductor. The N-channel is p/n:NTD3055L104 The P-channels are p/n:NTD20P06L. The op-amp is Microchip p/n:MCP6271-E/P.
The .zip file opens with Winzip or WinRar. The .sch and .brd files open with Cadsoft Eagle.
IT IS TOLD THAT LATER VERSIONS OF SOFTWARE DON'T HAVE THE CALIBRATION FACILITIES, THAT VER1.1 OR SOME VERSION HAD.
PLEASE READ THE picKIT2 RELATED INFO ON THE MICROCHIP FORUM
Joined: 08 Jun 2004 Posts: 324 Helped: 51 Location: Sao Paulo - Brasil
24 Feb 2008 1:18 Re: PicKit 2 FULL with TH components - Need help with layout
Check that the IRLML6402 mosfet replaced by the NTD20P06 is the voltage regulator element that makes the target Vdd variable. It acts as a variable resistor controlled by the amp op that has input coming from a PWM signal filtered by a RC network. Any difference in the specification of these mosfets can result to a different behavior of the voltage Vdd, not working as designed/programmed.
I did a fast read on the datasheets and I found some differences (for example: Threshold Vgs and on resistance).
Maybe using the correct parts or changing the feedback network resistors (e.g. R28) to a new adequate value will make a solution.
Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
25 Feb 2008 21:47 Re: PicKit 2 FULL with TH components - Need help with layout
I did some more tests and discovered that the output from the op-amp (the input to the NTD20P06) is 5.11v when 3v devices are selected and 3.66v when 5v devices are selected. Also, the datasheet of the NTD20P6 shows the gate threshold to be 1.5v compared to the .6v of the original part. The input and output capacitance is also slightly higher.
Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
28 Feb 2008 12:14 Re: PicKit 2 FULL with TH components - Need help with layout
SUCCESS!!!!!!!
I have discovered the problem. There is an error in my schematic. The drain and source of Q1 are reversed. The unit now calibrates and is fully functional!!! WOO-HOO!!!!!
Many thanks to all who helped. Special thanks to rkodaira for steering me in the right direction. I will post a corrected version of the .sch and .brd files and also a .pdf. Please feel free to improve the layout as needed.
Peace,
Computerman29
Added after 1 hours 52 minutes:
Here are the CORRECTED .sch and .brd files as promised. I cannot make .pdf files. Enjoy!
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Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
04 Mar 2008 6:04 Re: PicKit 2 FULL with TH components - Need help with layout
There is one more thing that I think I should point out to anybody who builds this:
OBSERVE THE POLARITY OF THE TRANSISTORS VERY CAREFULLY!!!!!!
The transistors in the circuit are ECB (not EBC like most others). They could easily be changed to avoid confusion or if BC639's and/or BC640's are unavailable locally. The only reason I used those transistors is because I was out of the 2N3904/2N3906's that I normally use. Have fun!!
04 Mar 2008 7:52 Re: PicKit 2 FULL with TH components - Need help with layout
Computerman29 wrote:
There is one more thing that I think I should point out to anybody who builds this:
OBSERVE THE POLARITY OF THE TRANSISTORS VERY CAREFULLY!!!!!!
The transistors in the circuit are ECB (not EBC like most others). They could easily be changed to avoid confusion or if BC639's and/or BC640's are unavailable locally. The only reason I used those transistors is because I was out of the 2N3904/2N3906's that I normally use. Have fun!!
Peace
Did you make a single sided PCB with all red wires hand wired with jumpers?
BTW, I have already indicated the need for checking the FET polarities in my post dated 28-2-08. That should be valid even for Transistors.
Congrats that you have made to work.
Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
04 Mar 2008 8:20 Re: PicKit 2 FULL with TH components - Need help with layout
Quote:
Did you make a single sided PCB with all red wires hand wired with jumpers?
Yes. That is correct. Quite a lot of jumpers, but it kept it single-sided. They seem to go all over the place, but I did not want to cross them and cause drc errors and other problems. Perhaps you or somebody else could do better. Like I said before, I am somewhat new to PCB layout design (but not to electronics).
Quote:
I have already indicated the need for checking the FET polarities in my post dated 28-2-08. That should be valid even for Transistors.
Yes you have, and it was that tip and rkodaira's mention of the function of Q1 that led me to the problem. Many thanks to both of you!! I was merely stating that the transistors in the schematic and layout use a different pinout than most general purpose transistors.
04 Mar 2008 10:12 Re: PicKit 2 FULL with TH components - Need help with layout
Computerman29 wrote:
Quote:
Did you make a single sided PCB with all red wires hand wired with jumpers?
Yes. That is correct. Quite a lot of jumpers, but it kept it single-sided. They seem to go all over the place, but I did not want to cross them and cause drc errors and other problems. Perhaps you or somebody else could do better. Like I said before, I am somewhat new to PCB layout design (but not to electronics).
................
Nice that being a newcomer to Eagle, you have taken up a large project and DID WELL I would say.
15 Apr 2008 5:13 PicKit 2 FULL with TH components - Need help with layout
Hi TS, can u translate the schematic and layout to pdf format as i dun have eagle. Or to a gif file?
THere is free pdf translator available, which is pdf995.
thanks.
15 Apr 2008 7:54 Re: PicKit 2 FULL with TH components - Need help with layout
wakaka wrote:
Hi TS, can u translate the schematic and layout to pdf format as i dun have eagle. Or to a gif file?
THere is free pdf translator available, which is pdf995.
thanks.
It would be better to install and use Eagle-The job wold be done and you learn too. the PDF converters carry some distortion as I experienced personally. Re-sizing would be a problem.
18 Apr 2008 1:39 Re: PicKit 2 FULL with TH components - Need help with layout
wakaka wrote:
i dun prefer to install eagle as I'm using P*otel now. So can anyone help? thanks.
wakaka-
Attached is the Picit2 PCB in P*otel 2.8 format and the schematic PDF. This is the same file posted earlier in this thread - it's just converted into a P*otel PCB for you with a PDF of the schematic since it can't be converted. Nothing is changed from Computerman29's original PCB file posted on 28 February except the jumpers have been moved to mechanical layer1 from the top copper layer to remove the shorts from the board.
There are lots of routing improvements that can be made, but that's up to you and the others who are interested in this board. I'm only providing the conversion services right now.
I saved the file in P*otel 2.8 ASCII format to permit folks to import it into all versions of P*otel or @ltium that have been released since version 2.8.
House_Cat
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Joined: 09 May 2007 Posts: 641 Helped: 15 Location: USA
18 Apr 2008 1:58 Re: PicKit 2 FULL with TH components - Need help with layout
Here is a you tube video on using an Au Group Electronics BB0703 (PICkit 2) to program a PIC without a PC:
(On the video a LED running code is programmed into a blank chip on a circuit board.)
18 Apr 2008 21:07 Re: PicKit 2 FULL with TH components - Need help with layout
To be honset that is the worse laid out PCB I have ever seen
and the board size is massive, The case would have to be big to fit it in, Sorry to say this but that's my 2 cents worth which is one more the funnynypd board
Why not buy the bare PCB form funnynypd, I f I remember it is on offer for 1cent
You could buy it and save yourself some time, It looks very nicley laid out and the video above just demo's how good it is with these new features, Program wihtout a PC
Joined: 09 May 2007 Posts: 641 Helped: 15 Location: USA
19 Apr 2008 3:41 Re: PicKit 2 FULL with TH components - Need help with layout
wizpic wrote:
To be honset that is the worse laid out PCB I have ever seen
and the board size is massive, The case would have to be big to fit it in, Sorry to say this but that's my 2 cents worth which is one more the funnynypd board
Why not buy the bare PCB form funnynypd, I f I remember it is on offer for 1cent
You could buy it and save yourself some time, It looks very nicley laid out and the video above just demo's how good it is with these new features, Program wihtout a PC
wizpic
I personally disagree.
We don't judge a design by size or shape. We do encourage people keep working and learning, especially at the beginning of a learning curve. It does take some time to make progress. I am pretty confident everyone of you will learn the skill-set one day and be able to do the fantastic job as many of our engineers do today.
Most of the engineers in my group went through the same learning curve as you did. So please don't give up.
Also Please don't be too upset. Once you have learned sth and gained some experience, that's a big achievement.
19 Apr 2008 8:27 Re: PicKit 2 FULL with TH components - Need help with layout
Quote:
I personally disagree.
We don't judge a design by size or shape. We do encourage people keep working and learning, especially at the beginning of a learning curve. It does take some time to make progress. I am pretty confident everyone of you will learn the skill-set one day and be able to do the fantastic job as many of our engineers do today.
Most of the engineers in my group went through the same learning curve as you did. So please don't give up.
Also Please don't be too upset. Once you have learned sth and gained some experience, that's a big achievement.
Having read it the second time and yes funnynypd is does sound very harsh and I would like to say sorry for my comments from above, You can give me a slap
I must if had one to many to drink
wizpic
19 Apr 2008 19:04 Re: PicKit 2 FULL with TH components - Need help with layout
Here is my version it's not single sided and it was designed to fit into a case I all ready use, all trhough hole compoents no SMT, I went double sided becasue I have got a tool that does it with out soldering both sides
wizpic
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Joined: 23 Jul 2006 Posts: 119 Helped: 4 Location: Valparaiso, IN USA
23 Apr 2008 13:32 Re: PicKit 2 FULL with TH components - Need help with layout
Hey wizpic,
It may not be pretty, but it works perfectly. For me, the size does not matter. I never planned on putting it in a case. I could have EASILY made it MUCH smaller if I used a two-sided board and/or SMT devices. The idea was to KEEP IT SINGLE SIDED so the average hobbiest could build it. It probably would have been much less trouble to just buy an original or a funnynypd clone, but as I have said in another post, Some people (like myself) just like to build things!!
To anybody who has read this topic, If you can make a better SINGLE-SIDED THROUGH-HOLED board, by all means go ahead.
And to anybody who does, I kindly ask that you share it.
