Any Ideas for a cheap touch sensor??????

[Byte_Butcher]

I will give it a try to Darrel Taylor's suggestion of using a 16F726 with a "capacitive sensing module" but I'm afraid that for this technique to work is going to require that your body has to be grounded.

Any comments on this issue or any related topic?????

No way! You shouldn't need your body grounded at all!

I'm testing the 16F726 touch sensor right now, using it to toggle a solid state relay on and off.

I'm sitting here in a carpeted room, on an insulated chair, wearing rubber soled sandals and the sensor works great!
My wife came in a little bit ago and it worked for her too.

I've got a simple 6 button "keypad" with bits of copper foil on the backside (inside) of a plastic box. When I touch the outside of the box where the sensors are... PRESTO... just like magic!

Try it. You'll like it.

[falingtrea]

Check out the Microchip M-touch pages. Seems to be a lot of implementation info there.

[rsocor01]

Yes, the PIC16F726 with a capacitive sensing module sounds like the best option.

What I meant by grounded is that in all the touch-button circuits I've tried they would only work if with one hand you touch the circuit's ground (negative lead of the power supply part of the circuit) and with your other hand you touch the touch-button or metal pad. It's like your body acting like a capacitor.

Robert

[Byte_Butcher]

No, there should be no need for any part of your body to be grounded or connected to circuit Vss or any of that. You should be able to just walk up to it on insulated feet and poke it with one finger, just like a "real button".

My buttons have a ground ring *around* them also, which helps a lot I think.

[Byte_Butcher]

FWIW, here's photos of my "test bed" for the touch sensors. On the front you can see it's just a plastic box. The black dots are at the centers of the touch pads. I'll come up with some nice stick on labels for the buttons later.


On the back you can see the six touch sensors... just little squares of sticky backed copper tape with a wire on each one. Just temporary to learn how it all works. The glue isn't all that good so I'll need something more permanent later.

Around the pads, you see the "ground ring" that surrounds it all. it's connected to system ground (Vss) and helps limit the range of the sensor so it doesn't overlap others nearby, and also seems to make individual pads more sensitive.


Dunno if that helps in your quest for a cheap touch sensor, but my tests so far with the 16F727 are good. A finger touch on any of the six sensor pads activates my routines real nice.

I like 'em a lot so far!


steve

[rsocor01]

Wow, I'm impressed with your project Byte_Butcher.

The ground around the pads prevents overlapping false alarms but also decreases sensitivity according to the next paper.

http://ww1.microchip.com/downloads/e...tes/01102a.pdf

There might be a tradeoff in there. Anyway, good job!!!!