The reason you cannot ground touch switches is due to the fact that if they were grounded, touching the switch would have no effect because any charge in your body would simply be grounded, and no signal would appear at the touch switch circuitry. It's probably cheaper all round if you make your own touch switches. (using the QTouch IC's would enable you to mount the electrode behind the glass to prevent any risk of electric shock). Membrane keypads would also be suitable for use (and cheaper).
Cheers SteveyG Could you tell me where I would find (or link me) to these QTouch IC's electrode switches. Mounting them behind glass would be nice!
http://uk.farnell.com/jsp/catalog/v...UJK1AJUPBP5QFIAEWSFE4AVAAS0IV3?prodId=4280192 Or go to www.farnell.co.uk and search for QT110 I think there are some others which have multiple channels on one IC to make the overall cost cheaper. QT150, QT160 are 5 and 6 channel devices if I remember correctly.
Thanks mate, That link you posted, do I have to put that whole electronic board behind the glass (as thats what the sensing pad is on, or is that not the sensing pad on the board) or can you get small stick on pads
I think the board in the picture is just an evaluation board. The actual QT1X0 is just an IC, which you can build onto your own PCB or stripboard. The electrode can be remote, so the circuit board can be hidden and the electrode connected with a sheilded wire.
Got you, saying that for 1.58 (I think that was the cost of the borad, ya cant beat it) Im sorry be a pain mate, but I dont know what Im looking for and cant find them. Could ya link me to the actually surface mounting sensors for IC chips
The sensor to connect to the chip can literally be made of anything metallic. You could cut some squares of thin aluminium/steel and solder a piece of wire to it, glue the square to the back of the glass and attach the other end of the wire to the chip. Due to the fact that it is a capacitive sensor, it isn't necessary to actually contact the metal with your finger - it can be activated by touching the opposite side of the glass which is ideal for this situation.
Really, wow, thats brill, perfect. So how do they actually work if its just a piece of metalic metal with only one lead coming out, dont it need 2 to complete a circuit
man, your a star, ya solved one of my biggest worries, cheers mate, the electronic world just gets better!!! Could I even just use a thin (ish) strand of wire (about the thickness of 15amp fuse wire or something) as the sensor, or does it need to be of a decent contact patch
I was looking at http://www.qprox.com/products/qt1xx.php and noticed that with a conductive contact (ie no dielectric in between)it can serve as a proximity sensor, so you just wave your hand bu a contact and it switches, If you can get some pieces of stainless that are isolated from ground and serve as touch pads you wouldnt even have to touch them. Now that is really neat. Oh no, I'm getting ideas, and that means that it is going to raise the cost of my new case that I am moding.
haha, sorry ConKbot of Doom, gotta see what you come up with though, bet it will be neat. Thing is, if the buttons are close'ish, wont there be a problem with setting off two bottom if you use proximity. And do the sensors have to be ontop of the dielectric material to work for proximity
so them evaluation boards you can buy, do there have all the electronic on them ready and set and it just a case of supplying an input, and the the out can just be sent stright to the serial port???
blimey!!! Ok so muppet over here (ME) got it wrong, them boards arnt just a few pounds, then are more like in the 50 - 100 pounds ranges......gulp. Can I get the chips on there own and make the circuit, or are the chips just as pricey!!!??????
The chips are just a few pounds, and then you can build them onto your own circuit board. If I remember correctly, the chips with 6 switches in each package include circuitry to take into account that your buttons might be placed close together, so only the input closest to your finger is activated: Part number 4269780 at farnell.co.uk is £2.57. This is the QT160-D with 6 channels (28 pin DIL).
Thanks for your help Steve. If you set them up to be proximity switches instead, do the sensors have to be on the top of the mounting surface rather than behind?? Also, can the sensor be as small as a single strand of wire say the thickness of 15amp fuse wire or something Also, I would probably go for the 16 channel chip, as I need 11 switches, and then that give me room incase I need anymore. Only thing is its a 44 pin chip (gulp), can you get 44 pin sockets or would I have to solder that with extreame care.....double gulp!!!
would a 44 pin chip be very hard to solder?? Would it be more ideal to us 2 6 channel chips to provide the 11 buttons Im after
I have used these chips extensivly and although they are pretty good they do require careful interfacing with whatever they are controlling. As a cheaper, possibly higher featured and probably more reliable method given your high humidity conditions, (these chips self calibrate at switch on but the build up of condensation may trigger them), how about remote control? This also has the added advantage of requiring no power supply in the humidity. Here is a possible solution but there are better.
I would prefer to have the touch buttons as it would go with my design. But do you feel that doing this (the chip) would be far to difficult??
What kind of package does the 44-pin chip come in? There are 44-pin sockets available for PLCC chips. They shouldn't pose any major soldering problems unless you're a total beginner. I can't see why a thin piece of wire wouldn't work, though it may require the glass to be thinner than if the electrode was of a bigger size. I think you may need to experiment a little with the chips.
