Touch sensors

Don_Kirby · Post by **Don_Kirby** » 24 October 2006, 18:24 PM

After reading the previous topic regarding rotary encoders, I was thinking about an ongoing project of mine that needs a user interface. I would appreciate any input on the following...

The device is a small, panel mounted display. I would like to add the ability to sense the user touching the display. I don't need location information, only touch or no touch.

I've researched the various types of touch sensors currently available off-the-shelf. The most promising are the capacitive sensors, which can turn just about any medium into a touch sensor. The problem is that they don't respond well to gloved hands. The sensor needs something conductive (even if only slightly so) to operate effectively. The format though, is perfect, the face of the display is the sensor, with no additional layers required.

Resistive sensors work well regardless of the object doing the touching, but having a custom sensor manufactured is beyond the scope of the project. I had considered getting large resistive sensor, and cutting it into smaller pieces, but attaching the necessary wires becomes an issue.

Optical sensors (emitter on one side, reciever on the other) would also work, but size is a major issue. To put this in perspective, the circuit board, running a ZX44, is roughly the size of a ZX24, including a much larger power supply, USB interface, power transistors, etc.. (Reflowing boards with components on boths sides is fun)

Mechanical methods are out of the question, unless a bonifide mechanical engineer, with access to the proper machinery cares to put in some volunteer work

So I'm open to suggestions of other technologies, mainstream or not, or any off-the-wall/hairbrained schemes.

-Don

DocJC · Post by **DocJC** » 24 October 2006, 19:29 PM

Don,
You seem to have touched (no pun intended) on all of the usual inputs. Purchasing an LCD with a touch interface built in would certainly solve your dilemma, although it would also take the fun out of it.
In addition to your suggestions one could also consider ultrasound. A large, gloved, hand may reflect enough signal to construct a suitable interface.
Depending on the environment it will be used in, one might also be able to wrap a coil of "magnetic" wire around the LCD, the ultra fine enamel insulated kind, incorporated in a tuned circuit. The proximity of the hand may detune the circuit enough to again offer a switching signal. Seems like a lot of work, however, to avoid a push button!
JC

pjc30943 · Post by **pjc30943** » 24 October 2006, 22:08 PM

Have you looked at electric field sensors?
They are easy to use, and will react to gloved and nongloved hands alike, in mostly arbitrarily definable detection spaces. Very versatile and easy to configure.
There are several evaluation kits available that make it reasonably quick to start with these sensors.

victorf · Post by **victorf** » 25 October 2006, 5:05 AM

How about one of these critters. Perhaps the -002 would do the trick?

http://www.ezlcd.com/

Vic

Don_Kirby · Post by **Don_Kirby** » 25 October 2006, 15:22 PM

victorf wrote:How about one of these critters. Perhaps the -002 would do the trick?

http://www.ezlcd.com/

Vic

Nice unit, but still too big.

Depending on the environment it will be used in, one might also be able to wrap a coil of "magnetic" wire around the LCD, the ultra fine enamel insulated kind, incorporated in a tuned circuit. The proximity of the hand may detune the circuit enough to again offer a switching signal.

That idea I like. I'll have todo some testing and see how it will deal with harsh environments, as well as the glove issue.

Have you looked at electric field sensors?

I hadn't until now. Seems to work much like a capacitive sensor, but using impedance. Thanks for the tip.

-Don