AnsweredHot!mTouch without cap sense module? confused on peripheral requirements

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luxfx
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2018/07/26 10:12:56 (permalink)
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mTouch without cap sense module? confused on peripheral requirements

I have a Curiosity DM164137 board with PIC16F1619. The board has a sense pad that I've gotten working as both button and proximity sensor using mTouch installed through MCC in MPLAB X IDE v4.20.
 
The thing is, I can't find anything in the PIC16F1619 datasheet referring to mTouch (except for a trademark notice) or cap sense / CPS. On the other hand, the PIC16F1824 datasheet, another chip I've used mTouch on before, lists 8 capsense channels in the datasheet, mentions mTouch in the overview, and includes a chapter on CPS usage.
 
So what's going on with the 1619? How is it even working? Does the mTouch library bitbang ADC channels to fake it if the chip doesn't have CPS?
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charlie0
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Re: mTouch without cap sense module? confused on peripheral requirements 2018/08/10 08:42:49 (permalink)
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I believe any device with an ADC is capable of using the mTouch Library.  It's nice if the device has a peripheral such as the CVD however, to offload the cap sense processing off of the core. 
 
This manual might help explain how the PIC16F1619 handles cap sense:
 
http://www.microchip.com/...devicedoc/en534865.pdf
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XiangGao
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Re: mTouch without cap sense module? confused on peripheral requirements 2018/08/10 11:13:06 (permalink) ☼ Best Answerby luxfx 2018/08/10 11:44:33
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Hi Luxfx,
 
There are many ways of doing capacitive touch. In the past days, Microchip tried the oscillation based method using the CSM module as you saw in the PIC16F1824 datasheet. However, this is not recommended anymore due to its poor noise immunity. 
 
Microchip has been using CVD method 7 years ago, which provides more robust touch performance. 
To perform CVD, you only need a 10-bit SAR ADC, and this is what mTouch library is using. Like you said this is pretty much bit-banged capacitive measurement.
 
To get better performance, Microchip has designed chips that have hardware CVD modules, like PIC16LF1554/9.
All the ADC with computation devices has hardware CVD module as well, like PIC16F18446.
 
Details of CVD: http://www.microchip.com/....aspx?appnote=en560193
 
-Xiang
post edited by XiangGao - 2018/08/10 12:40:15
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luxfx
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Re: mTouch without cap sense module? confused on peripheral requirements 2018/08/10 11:44:59 (permalink)
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Thank you Xiang and charlie0 -- very helpful info!
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