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

[peterdeco1]

Hi Robert. Here's a link to the datasheet for the QT102 touch switch.

http://www.qprox.com/assets/Download...3.05-15437.pdf

[Byte_Butcher]

OK Darrel, I posted my code.
http://www.picbasic.co.uk/forum/show...1611#post71611

I'm sure it needs a LOT of fixing to be "good", but it's functional enough now to make a touch sensor work. Enjoy!


Steve

[Darrel Taylor]

OK Darrel, I posted my code.
http://www.picbasic.co.uk/forum/show...1611#post71611

Awwww, you weren't even in the "Hot Seat" long enough for the seat to get hot.

Sweet!
<br>

[rsocor01]

Thank you all for your prompt responses.

Well, I'm still struggling trying to make this touch circuit to work. I have tried different circuits with op-amps and ne555 chips but the main problem with these circuits is that your body must be grounded for the switch to work and this is not what I'm looking for.

I read Peterdeco1 suggestion about using a QT102 but that chip is too expensive ($20+ at mouser.com) and it would add more components to the final design. 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?????

Robert.

[Ioannis]

May be then you need inductive and not capacitive sensor.

Look at Microchip for this new technology.

It has + and - as it is for the Capacitive sensor too.

Ioannis

[Archangel]

I remember, about 35 years ago working on an autopilot for my Dads boat, using a simple 2 transistor switching circuit, it was too sensitive and responded to touch, cured it with proper biasing resistor. BTW I was not grounded. You could put a groundplane and sense wire together coaxially or using spiral technique.

[Darrel Taylor]

... 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.

This statement in the datasheet seems to indicate a ground isn't required ...

The capacitive sensing module allows for an interaction
with an end user without a mechanical interface. In a
typical application, the capacitive sensing module is
attached to a pad on a printed circuit board (PCB), which
is electrically isolated from the end user.

[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]

Hi Robert. Here's a link to the datasheet for the QT102 touch switch.

http://www.qprox.com/assets/Download...3.05-15437.pdf

I've used those QT102's before (and QT150, which is a 5 channel version). They work pretty well, but they aren't as cheap as using a 16F727 and it adds more parts to your circuit.

You might want to check the Atmel website... I think the QT102 has been superseded by a newer part and isn't recommended for "new designs".
Maybe I'm wrong...