Through glass touch sensor

wardbob

Member
Hi, I just checked and found out the last time I was on the Forum was 5 years ago! I am back into PICaxe due to a project.

A few years ago, someone mentioned the QT113-D touch sensor, which can detect touches through as much as 100mm (4") thick glass or plastic. Here's one US vendor.

http://www.parallaxdirect.com/cart/catalog/Parallax-604-00038-QT113-D-Touch-Sensor-248.html

I need to make a sensor that can detect finger touches through 6 mm (1/4 ") thick glass. Everything has to be behind the glass and no holes can be made in the glass or the frame.

Has anyone used this sensor with a PIXaxe or has anyone figured any other way to accomplish this task?
 

nick12ab

Senior Member
Have you noticed that the latest PICAXEs have built-in touch sensors? It might just work for 6mm glass. You could try it first before splashing out on that sensor since you'll be using a PICAXE anyway.
 

wardbob

Member
I did see that the new M2 chips have a touch sensor. They listed it for 3 mm. I will try it out at 6 mm. I'm hoping the 3 mm was a bit conservative. Anyway, I imagine I could figure out a way to push it to 6 mm.

I only have the old versions but some M2 are on the way. I'll let you know when I get the new ones.

Thanks!
 

jinx

Senior Member
Just did a test "well the other day" using 18m2 where i taped some wire to some 6mm glass and can confirm that it works.
 

boriz

Senior Member
I designed a through-plate-glass keypad ages ago. It was optical. Each sensor had an IR TX and RX right beside it. The idea being that the fingertip will reflect much more IR than the uncovered glass. This was long before Picaxe TOUCH was introduced.
 

wardbob

Member
Jinx,
Thanks! That's what I was hoping. My new batch of PIXaxes should arrive shortly so I can continue with my plans.
 

wardbob

Member
Boriz, that was my plan if the touch sensor didn't work. Do you recall what IR TX you used? I know glass absorbs some IR but it varies with wavelength. You obviously got enough through the glass for it to work. Did you use some kind of coding to prevent it being triggered by other sources?
 

boriz

Senior Member
Never built. Just played around, proved the principle then got bored and moved on. It was ultimately supposed to be the interface to an interactive shop window display.

Anything but direct sunlight should have a high enough S/N ratio. Otherwise you might need modulation.
 

Paix

Senior Member
@Wardbob, Welcome back. can you put a location or country on your profile so that things like suppliers can be more appropriatly cited for you.

I have been playing with a LED as a combined display and sensor very recently. Extending on the work of Wilf Ritger with his dark sensing circuit of 2007.
The circuit is simply changed to light sensing by XORing the LED anode with 0 instead of 1. So a bit of a no-brainer there. I assigned the result to a variable instead of directly to the pin and so was able to copy it to the pin and to report it to the screen monitor using sertxd. Most of my testing was in my living room in the evening so the lights were on and with a 5mm water clear green LED. Before I adapted the code, it also worked eminently with a 5mm coloured red LED package and a 3mm coloured yellow LED package.

My code changes are on a netbook, elsewhere at the moment, (I'm too idle to reach for it) so I will post them tomorrow, but to be going on with, here is Wilf's circuit and comments - take the nap time comments as out of date!
I found in the first nap that 2 became unstable, 3 was good and as I went towards a max of 7 the sensitivity dropped away significantly. 08M parts are max nap 7. 08M2 go out to 40 seconds, but I'm currently using a spare 08M. The second nap had the effect of extending the LED on time. With a maximum of 7, I changed this figure carefully as there was no current limiting resistor on the LED. I suspect that with an 08M2 that you could damage the LED, so take care.

I think that with an illuminating LED and sensor aided through glass, that a finger could reflect sufficient light to be used for switch selection. An audible feedback would give it a better performance curve I think. After the DO statement, add sertxd (#b0, " ") and change pinC.2=pinC.2 xor 1 to b0=pinC.2 xor 1 xor 0 for a light sensor. This will leave the LED as a sensor only, so adding the line pinC.2=b0 will bring back flashing and of course untested but pinC.2=not b0 will change the phase of the flashing but might turn out to be really useful or disterous and self defeating. I have yet to check out that option.

I'm sure that you get the idea and I'll report back as soon as I have made the tests tomorrow, Wednesday or Thursday at the latest. Watching the changes 0 to 1 in the monitor is instructive.

G313.pngHave fun!

It also works with the AXE027 attached and the 10k/22k resistors connected. leaving pin3 /C.3 floating isn't an issue. So other than the basic download circuit all you need is your selected LED. The cathode has the shorter lead (until you clip it) and yes I had to check that, twice! The cathode is the anvil which will still be the same long after the leads have been clipped.
 

Dippy

Moderator
Before QProx brought their stuff out I used IRLED into edge of acrylic.
Most IR was internally reflected and didn't pop out
When you shove your finger onto surface it changes the interface and the IR 'comes out sideways'.
It kind of worked but I never go it sussed properly.
I think it is used in some products.
 

SAborn

Senior Member
Good concept Dippy, never thought about it before but that makes perfect sense, i think some optical fluid sensors work on a similar method.
 

wardbob

Member
Will add location info to profile. But for now, I'm in the USA in the Cleveland, Ohio, area. Just south of Lake Erie. We have some great winter snow.
 

wardbob

Member
Paix,
I forgot to mention, thanks for the reflection based sensor info. I just was looking at the touch sensor section of the PIXaxe manual and saw a mention of the touch sensor not working when wet. I will have to test that, since the odds are very good the shop window will be frequently wet from blowing rain and snow.

The refection system you presented looks like a good possibility. Thanks for the diagram and the detailed suggestions. I'm a bit rusty on the PICaxe BASIC as I have been away for 6-7 years, but I'll get back.

My new chips came yesterday (from the people who are running Peter Henderson's business) so I will start to play around tonight with touch and reflection both.
 

erco

Senior Member
Interesting problem, is this for an interactive store window? I have done some interesting projects with the M2 touch sensors. I'm pretty sure that rainwater on the window would affect both PicAxe touch sensor reading and a reflection-based sensor. Calibration could help reduce false triggering. You might also consider using Rain-X glass treatment on your window, which discourages water from sticking.

http://www.rainx.com/products/glass-and-cleaners/
 

Paix

Senior Member
I guess that moisture or rain dripping down the outside of the window might be considered to be a form of random animation for a window display. Enjoy, then wipe and key your selections. :)
 

wardbob

Member
Interesting problem, is this for an interactive store window?
Yes. Since we have a rainy/snowy early winter, the window stands a large chance of being wet. Rather than spend the time setting it up and having it go bad, I am going with a push button. We have found a small opening at the top of the window to run the wire.
 

Hemi345

Senior Member
Yes. Since we have a rainy/snowy early winter, the window stands a large chance of being wet. Rather than spend the time setting it up and having it go bad, I am going with a push button. We have found a small opening at the top of the window to run the wire.
Ahh, where's the fun in that?! I think a PICAXE operated squeegee or a little robotic arm that hands them a towel to clear the window would be more fun. :)
 
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