QTouch issues with AVR128DA28

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I am working on a 4x4 QMatrix with an AVR128DA28.

I run a project generated by Atmel START with example code and monitor the status of each pad with a data visualizer.

There is no problem so far under careful use.

 

I put my hand on the entire pad, assuming the device is in pocket.

The problem arises here.

Some buttons do not return to OFF even after releasing my hand.

The PTC (Peripheral Touch Controller) is a black box and I don't know what's going on inside.

Does anyone know how to adjust or restore?

 

Touchpads

 

 

Normal (touching button 0)

 

 

The data after I release my hand stays above the threshold and remains perceived as "touching".

 

 

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This is probably something you're going to have to take to Microchip for specialist support.

 

There is a 'Touch' forum, but it seems pretty deserted:

 

https://community.atmel.com/capacitive-touch

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awneil wrote:
There is a 'Touch' forum, but it seems pretty deserted:
If you like I could move the post to there (but leave a "trace entry behind here i nAVR/Xmega") but I can't help thinking the thread would end up blowing down main street with the tumbleweeds ?? (unless Microchip have someone who "watches" that Touch forum for activity?)

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clawson wrote:
I can't help thinking the thread would end up blowing down main street with the tumbleweeds ??

Sadly, I think you're right there.  frown

 

Perhaps  kabasan  could put a brief post there, linking to this?

 

something like this: https://www.avrfreaks.net/forum/dgi-data-visualiser-not-working-xplained-pro 

 

(unless Microchip have someone who "watches" that Touch forum for activity?)

doesn't seem to be the case.  frown

 

I think a direct support case is probably the way to go (which is how my DGI problem was resolved).

 

Or, if   kabasan  has a technical distributor, they might be able to help ...

 

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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Yes, I don't expect touch forums too.
And I'm thinking of moving to a direct support case.
Before that, I posted it to see if it was my simple ignorance.

I have no experience with older Qtouch ADCs. Therefore, this phenomenon cannot be understood at all.

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kabasan wrote:
The PTC (Peripheral Touch Controller) is a black box ...
with a tuning procedure.

PTC arrived with mega328PB; PB megaAVR were announced near Atmel's EOL.

kabasan wrote:
Touchpads
too much capacitance?

Touch sensors can be one-layer.

 


AT09363: PTC Robustness Design Guide

[page 15]

Figure 2-12. PTC Tuning Flow Chart

 

Coplanar (One-layer) Design | AT11805: Capacitive Touch Long Slider Design with PTC

though

Hardware Setup | Touchpad With Built-In Surface Gesture Recognition Using Peripheral Touch Controller (4x4 mutual capacitance)

 

"Dare to be naïve." - Buckminster Fuller

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kabasan wrote:
Therefore, this phenomenon cannot be understood at all.
AVR Dx are low (very?) leakage.

A guess is there's a discharge phase in PTC's state.

 

I/O Pin Characteristics | AVR® DA Family

5nA typical at 85C is 5nA/(2 ^ (85C - 25C)/10C) = 78pA typical at 25C (approximate to the bias current for an inexpensive zero-drift op amp)

 

"Dare to be naïve." - Buckminster Fuller

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Back layer is an X-line to block the effects.

It follows the design guidelines of the app note.

The X-Y capacity of each pad is about 3pF.

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I studied a little.

Problem # 1 was improved by setting the internal series resistance of the Y line to 20k. It's very stable.

I also found that the key node can be initialized with calibrate_node (node num).

My application needs to judge the situation (pocket in, cover with hand, etc.) from the input state of the touch button and cancel the input appropriately.