Simple Capacitive Touch Sensor

william chan

Hi All,

I am hoping to slowly ramp up the clocking freq until the input detects a high.
Then reduce the freq a little until the input becomes low again.
Then wait for any fingers to come close to increase the capacitance which will make the input detect high.
Can such a circuit work?

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www.fd.com.my
www.mercedes.com.my

nohab

Have you seen this?

http://obex.parallax.com/objects/309/

william chan

Thanks.
I guess that was a simpler circuit.

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www.fd.com.my
www.mercedes.com.my

Beau Schwabe

william,

Here is an interesting article that I have been holding on to, that covers a little bit of theory with capacitive sensors.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

bluesparq

Check out www.TouchSwitch.net
They have a lot of capacitive touch offering.

BigFoot

STM has some interesting chips that would work with the Propeller to implement a touch based system.

BigFoot

william chan wrote: »

Hi All,

I am hoping to slowly ramp up the clocking freq until the input detects a high.
Then reduce the freq a little until the input becomes low again.
Then wait for any fingers to come close to increase the capacitance which will make the input detect high.
Can such a circuit work?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my

Here is another way to do touch controls for a surface mounted switch. This one was used
in a custom home shower to select your personal water temperature. We also used it to open a massive front door. It is completely water resistant.

The propeller transmits a signal down the twisted pair which couples back into the input.
When the disk is touched it shorts the weak coupled signal to ground, activating the
switch. We used Cmos logic & 6800's back then but the Propeller input has a high enough
input resistance.