Home built PickIt2 not behaving normally.

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi All,
I am having a strange problem with a homebuilt PickIt2. It is wired just as MicroChip designed it, but I substituted a few parts to facilitate thru hole construction. I subbed a BS250P P channel MOSFET for the IRLML6402 and the Q2 part of U5, and a TN0702N3 for the Q1 part of U5. I also subbed a MCP6041 op amp for the MCP6001 op amp. The board is recognized by the PickIt2 v2.61 software. The problems are as follows:

1) When first plugged I get the error message bo that says "Pickit 2 VDD voltage level error. Check target and retry operation." I get this error message whether a PIC is connected or not.

2) When I hit OK the PickIt 2 Programmer software runs and shows that a PickIt 2 was found and connected. Sometimes it finds a connected device, other times it doesn't.

3) If it finds a device, pressing Erase or Blank Check brings up the VDD error box again, and then the software reports "No device detected".

When I run the troubleshooter, the following occurs:

Step 1 passes but I always have about .2V difference between what I set and what I read in the results bo and on my DMM.
Step 2 Pressing "Test VPP" the first time gives me a "Test Failed: VDD Short Detected" error. I can see with my scope that the level is high, and I can measure around +12V with the DMM. If I press "Test VPP" a second time it reports that the test passed with a voltage reading close to what I get on my DMM. When I press "/MCLR On" the VPP level drops to 0.
Step 3 I can control the PGC and PGD lines during step 3 testing.

I feel that Step 2 is the main problem, but tracing my connections has shown no miswires. Plus if there was a miswire, just running the step a second timee would not pass the test.
Did one of my substitutions break something?
Any ideas on how to get this working would be greatly appreciated.

Thanks for reading!
Regards,
Mike
 

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi spinnaker and R!f@@,
I am an old school type. I like to build my own stuff. It is wired correctly. Someone on another forum pointed out that the MOSFET that I substituted for has an RdsOn of 65mOhms, and the one that I used has an RdsOn of 14 Ohms. I am going to order the correct part and then I will report back.
I picked subs because I wanted to try using all thru hole parts. This part comes in a SOT 23, so I will be using a SOT 23 to DIP adapter.
Thanks for reading.
Regards,
Mike
 

DickCappels

Joined Aug 21, 2008
6,389
Be patient and don't be too discouraged, there is a good chance that somebody who understands or can figure out the problem will come along.

Toward that end, it would probably help if you post some details of the design or a link to the project.
 

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi DickCappels,
Thanks for the response. The schematic is out of the MicroChip PickIt2 User's Guide pages 81-82. I just swapped out leaded partd for the SMT ones, the MOSFETs and the op amp. It was pointed out to me about a parametric disparity between the IRLML6402 and a BS 250 that I subbed for it. The RdsOn for the IRLML6402 is 65mOhm and the RdsOn for the BS 250 is 14 ohms. So I will order the SMT part and report back to this forum.
Regards,
Mike
 

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi R!f@@,
Yes I did.
The RdsOn for the IRLML6402 is 65mOhm and the RdsOn for the BS 250 is 14 ohms. So I will order the SMT part and report back to this forum.
Regards,
Mike
 

takao21203

Joined Apr 28, 2012
3,695
shouldnt make a difference since sourced currents are negible. The OpAmp behaves differently you need to dig into the firmware and find out whats happening, and the UI software on the Windows side as well.

Theres certain sections dealing with detection of erroneous conditions you need to examine these.
 

be80be

Joined Jul 5, 2008
2,042
Pickit 2 VDD voltage level error that only happens when the pickit is reading a short or a powered target
But the rest of the list sounds more like a USb problem.
I've made a bunch of these clones and they work fine but at first i had some of the problems your talking about
to long of usb cord caused a lot of them to not work and the D+ And D- lines like to be side by side and the same link.
 

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi takao21203,
Thanks for the response. Looking at the output of the op amp with my scope shows a wonky waveform. Perhaps that 14 ohm RdsOn is causing problems. I have ordered the correct part with 65m ohm RdsOn, and then we shall see if that fixes the problem.

Hi be80be,
Thanks for answering another one of my posts again! I have built a clone of your circuit where you have to manually select 3.3 or 5 volts, and it works great! I just wanted to have an "original" where I could software control the VDD and have the programmer to go functionality. I am pretty sure it is the MOSFET that I am using in the VDD_TGT circuit. The one that I am using, a BS250P, has an RdsOn of 14 ohms. The specced one, an IRLML6402, has an RdsOn of 65m ohms. I have ordered some IRLML6402, and when I get them installed I will report back to this forum.
 

takao21203

Joined Apr 28, 2012
3,695
Ive once built a RS232 PIC programmer and flashed 16F716 with it no difficulties.

Modified the circuit on the fly- generating VPP from 2xAAA batteries, a transistor and two coils.
The circuit was such it could power the PIC as well when flashed- the high voltage would break down to a few volts, only about 1mA are needed. The softwares for these old style programmers are not really good but also its just a few chips they support.

The PICKIT programmers dont show the current but most small PIC circuits can be powered directly.

Vpp I have seen complicated approaches but a booster that simply breaks down in relation to voltage if any larger currents are drawn is quite effective.

Yet the approach for professional programming modules is not minimizing the design but professional reliability and adherance to design rules goals and engineering standards.

I pushed the well known joule thief even further- no resistor and capable to generate 100 volts using a plain 2n3906 using 2xAA batteries (NiMH) is not too bad.

With the PICKIT designs same would be possible, removing component after component so as such, after a while less than nothing will be left on the PCB, dont even need any kind of circuit board. But again thats not the design goal, guess.
 

JohnInTX

Joined Jun 26, 2012
4,085
With the PICKIT designs same would be possible, removing component after component so as such, after a while less than nothing will be left on the PCB, dont even need any kind of circuit board. But again thats not the design goal, guess.
But it could be. We old guys used to call that 'Muntzing'.
But for building one PK2 clone, parts reduction less important than it working.
 

PICNewbee

Joined Mar 31, 2017
355
"call that 'Muntzing'."

There building was still there when I left LA in '92.

By the Santa Monica airport.

It said Lear something maybe.

Nice to work in electronics about Oh let me see 26 blocks from the beach.
 

PICNewbee

Joined Mar 31, 2017
355
Mike

Since it sounds like you have retired recently.

Is being able to handle a soldering iron disappearing from American tech businesses?

Replaced with circuit design programs and soldering done overseas?

Or is that just dark imaginings?
 

Thread Starter

mikejp56

Joined Jun 14, 2015
63
Hi PICNewbee,
I am still working, although getting close! I am old school...soldering iron and analog scope old school. Not like these kids today who don't know how to use a VOM.
Regards,
Mike
 

panic mode

Joined Oct 10, 2011
1,831
i made few and they all work fine... first one was a prototype done using through hole components and single sided PCB. next version was using SMT and smaller USB connector.
btw. all transistors are BJT pulled from some random PCB.PicKit2 PCB component side.jpg
 
Last edited:

Thread Starter

mikejp56

Joined Jun 14, 2015
63
i made few and they all work fine... first one was a prototype done using through hole components and single sided PCB. next version was using SMT and smaller USB connector.
btw. all transistors are BJT pulled from some random PCB.View attachment 128127
Hi panic mode,
Thanks for the photo. Mine has both MOSFETs and bipolars. I just need to get the correct MOSFETS!
Regards,
Mike
 
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