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Debugging touch paddles stuck "on"

John Laur
 

Per the subject of my email, I built my Morserino-32 kit, but the touch paddles are stuck "on," and I get a constant stream of dit-dah as a result. It does not matter if the paddles are plugged into the sockets or not. I have double checked for any bridging or pcb defect but cannot spot anything with a visual inspection. I am curious if anyone else has had the problem or if there was a suggested course of action for debugging. The schematic could not be simpler here so there doesn't seem that there is much that could go wrong-- I have already verified that there is no short between GND and pins 2 or 12 of the module, so I am suspecting some other problem.

I have not obtained a battery yet, so I have been powering with a high quality USB power bank. I suspected that might be interfering with the capacitive touch detection, so I tried a different high quality apple iPad USB supply with the same result. External iambic paddles perform as expected. I did order two kits, so I can build a second unit and identify where the problem may be.

73,
John K5IT

Karsten, DD1KT
 

Hello John,

after looking a little deeper into the schematic and the Pin definition of the Heltec Module it looks like the Touch functionality is defined inside the µC.

So not only a short can disturb the function but also a leakage current on the pins 2 and 12. After checking for shorts (as you did), I would check for the resistance between the pins and GND ( board not powered). Having a 2nd  set, you can also check if the change of the Heltec module will cancel the problem or it stays. 

If nothing is wrong with the PCB and the change of the Heltec module cancels the problem,  the only try is to clean the module (way of pins to the µC) with PCB cleaner (mostly alcohol). 
I do not believe, that the power supply can disturb the function: I was running the module without battery from the USB port of my desktop without issues. 

Good Luck

vy 73 de Karsten, DD1KT

 

Willi, OE1WKL
 

Hi all,

This is an effect I have not seen so far at all. As the touch paddles are - to a certain extent - self-calibrating, you could try the following: in Keyer mode, when you hear the stream of dits and dahs, touch both paddles for a couple of seconds. Maybe, when you stop touching them, the dits and dahs stop?

The power supply almost certainly can not influence the behavior of the paddles to such an extent.

73

Willi


Am 27.06.2019 um 00:45 schrieb Karsten, DD1KT <ktholmann@...>:

Hello John,

after looking a little deeper into the schematic and the Pin definition of the Heltec Module it looks like the Touch functionality is defined inside the µC.

So not only a short can disturb the function but also a leakage current on the pins 2 and 12. After checking for shorts (as you did), I would check for the resistance between the pins and GND ( board not powered). Having a 2nd  set, you can also check if the change of the Heltec module will cancel the problem or it stays. 

If nothing is wrong with the PCB and the change of the Heltec module cancels the problem,  the only try is to clean the module (way of pins to the µC) with PCB cleaner (mostly alcohol). 
I do not believe, that the power supply can disturb the function: I was running the module without battery from the USB port of my desktop without issues. 

Good Luck

vy 73 de Karsten, DD1KT