Capacitive Touch Membrane Switch

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Hi All:

 

We're looking forward to upgrade our system keypads from 4x4 matrix membrane  to Capacitive Touch Membrane Switch looking for durability and other benefits. 
We tried a TTP229 based module to input each individual key and read the information through the I2C interface on the module. 

While we can interface the module and read Ko..K15 when finger touching the pins, but when we connect the keypad below we have no readings (Keypad has an Autotex F200 Graphic Overlay ).

 

connecting only one track of the keypad connector to the TTP229 module (K0) we found that it continuously read the key even when not touched. We change capacitors on the module to change sensibility and go from continous reading to no sensing. 
Common trace on the keypad is not used with this module, and perhaps that's the missing part to make it work. Perhaps we're using the wrong module and need to change the circuit.
I post my case  in the belief that many designers are facing the same problem migrating from matrix to touch keypads.
Any feedback will be greatly  appreciated.

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Have you asked the manufacturers? Does this have anything to do with AVR?

Common trace on the keypad is not used with this module

And why not? Do you connect just one wire to a battery and expect to get any power out of it?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Main system is based on an ATMEGA128 and my tought is that maybe I can get some feedback from people using the Atmel Qtouch technologies.
Unfortunately Touch keypad manufacturer gives no feedback on circuitry to read this units. RobotDyn module is manufactured as a finished product and have no help neither.
The keypad is only conductive traces, it's not powered at all. Whats powered is the TPP229 module with +5V and Gnd. The module is supposed to read the capacitive changes on the keypad electrodes (pads), but not happening. I'm looking forward for advise on Atmel technology to read touch devices like this.

Last Edited: Sat. Sep 9, 2017 - 08:28 PM
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But if you don't connect the common ground the keypad is just a huge antenna, it's a simple thing to do!

I'm looking forward for advise on Atmel technology

Why? I don't see an Atmel logo on the touch controller.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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electrocoder wrote:
I'm looking forward for advise on Atmel technology to read touch devices like this.
Microchip is adding Peripheral Touch Controller (PTC) to some PB megaAVR and most tinyAVR 1-series.

tiny417 has a PTC; could have the tiny417 interface the keypad and do board controller functions (Configurable Custom Logic (CCL) and etc)

tiny817 Xplained Mini has two touch pads, is at very low price, and runs on 5V from USB VBUS.

tiny817 Xplained Pro also has two touch pads but it's at 3.3V

Source code in Atmel START for both boards.

Schematics and PCB layers are in the hardware archive for both boards.

 

http://www.microchip.com/wwwproducts/en/ATTINY417

https://octopart.com/search?q=ATTINY417&start=0&avg_avail=(1__*)

http://start.atmel.com/#examples/touch

 

"Dare to be naïve." - Buckminster Fuller

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Thank you, your reply is of great help. I needed a hint where to start researching for a solution.

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I tried common ground to keypad yesterday  when testing but still no output.
touch controller is not Atmel's. My goal is to replace this  circuit that did not do  the job with Atmel's QTouch.
Useful posts start showing up in the discussion. When I find the solution I'll post it for the reference of the users. 

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My goal is to replace this  circuit that did not do  the job with Atmel's QTouch.

Then you should read Atmel's application notes and use a NEWER chip that makes it easier to use touch, the M128 is as old as the hills.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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With 1000's of systems installed  throughout the country is not easy  to ask the customers to change the whole system just to make the keypad "touch". The goal is to add a controller board that talks I2C with the main system and read the touch keypad as I said earlier.
 

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Your membrane looks like it is for mechanical switches not touch switches. Look at the pcb that uses the tt229 chip and has the keypad on the pcb. Those touch switches look nothing like yours.

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Some really good information here:

 

https://community.particle.io/t/...

 

More info here:

 

http://itimewaste.blogspot.com/2...

 

Supposed Arduino Library:

 

https://github.com/arduino12/ttp...

 

 

 

Lee has done Qtouch on a few of his products so when he logs on next time he might be able to shed some insights on Qtouch.  If you are looking to go the QTOUCH path then this thread will be moved to the Qtouch community.  If you want to stick with the Board in your OP then thats another story.

 

From what I see from the datasheet the part seems pretty straightforward to use.  I agree with Kartman that your keypad is not close to what you need.

 

 

wish I had some time - and funds, to order one of these boards, and a few chips too.  This could save me some headaches.  Or create new ones surprise

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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This is one of my touch board, it used the old QT160 chip before Atmel took them over.

 

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly