Author Topic: Touch sensor  (Read 2366 times)

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Offline akis

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Touch sensor
« on: October 05, 2014, 04:29:01 pm »
I have never used a touch sensor before, I want to use it as an on-off switch, I will connect it to the analog or digital input of a PIC so as long as I can detect a change in voltage that is all I need. I am not sure how touch sensors work, but looking on ebay they appear to be much more complicated than a simple on/off switch. Can someone please help?
 

Offline electr_peter

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Re: Touch sensor
« Reply #1 on: October 05, 2014, 04:38:52 pm »
You can find simple touch sensor modules on eBay. http://www.ebay.com/itm/1pc-Switch-Digital-Touch-TTP223-Capacitive-Touch-Sensor-Module-For-Arduino-/351093750132?pt=AU_Gadgets&hash=item51bed17974

"Switch Digital Touch TTP223 Capacitive Touch Sensor"
These can be configured via two pins to be either alternating on/off (think them to be a latched switch) or momentary switch. I tried those, they have some autocalibration built-in.

If you would like to roll your own capacitive touch, try reading app notes of TI MSP430 captouch capabilities.
 

Offline akis

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Re: Touch sensor
« Reply #2 on: October 05, 2014, 05:03:52 pm »
I have read it now : I apply power to it, and when someone touches it,  it goes high, 0.8V, and after 12 secs it goes low to 0.3V. I can then compare this voltage with an op-amp or the analog input of a PIC. Am I right or am I missing something ?
 

Offline electr_peter

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Re: Touch sensor
« Reply #3 on: October 05, 2014, 05:12:51 pm »
I have read it now : I apply power to it, and when someone touches it,  it goes high, 0.8V, and after 12 secs it goes low to 0.3V. I can then compare this voltage with an op-amp or the analog input of a PIC. Am I right or am I missing something ?
I am not sure about information source you read, but particular module on eBay outputs close to VDD/VEE (because it has some transistor buffer stage).
Previously mentioned TTP223 module outputs logic high or low at voltages close to full VDD(positive rail) and VEE(ground). Just apply power to this module and connect output from this module to digital input of MCU. It should do.
If it doesn't work, check voltage levels on the output.

TTP223 has 4 operating modes, set by two jumpers (solder bridges) right on the board. One jumper sets latched/momentary operation, other selects default output state (either high or low).
 

Offline akis

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Re: Touch sensor
« Reply #4 on: October 05, 2014, 06:25:37 pm »
I read the same but, originally, misunderstood the specs...

http://www.ebay.co.uk/itm/400624301894?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Thanks for the help, I have ordered two of these
 


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