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Using touch switch for eject button?

H

hctimo787

n00b
Joined
Aug 12, 2004
Messages
41
Hi. I don't know how feasible it is, but I'd like to try using a contact/touch switch rig on a stealth drive bay cover to use for opening/closing a DVD drive (or two). I've seen kits online for the switches, but they say 1" ² for the touch plate, would a 5.25" drive bay cover work (with conductive paint)? I'd love to have something like this, and have it work. Then there would be no need to an externally mounted or internally mounted mechanical switch. How cool would that be. Anyhow, here is one of the kits I came across...

http://store.qkits.com/moreinfo.cfm/QK137
http://www.electronics123.com/amazon/datasheet/k137.pdf

qk137.jpg


THOUGHTS?
 
if your new to electronics, i would suggest you get one of the kits, otherwise here are two circuts for you, that you can build yourself... this first one uses a "2n319" FET transistor:
2n319switch.jpg

and this one uses a CMOS logic gate 4011:
cmosswitch.jpg

both of these circuts have ground wires. this is only to ensure that your finger has electrical potential. you can, in both cases, hook the circut's ground line
to your case ground(thus the carpet, floor...). just make sure you have something (like foam tape) to stop the metal plate from contacting the metal case

about the 1" square... these devices work off of static electrisity building up potential in your body. the problem with using a whole drive bay as a pad is that it would take a LOT of static to charge the plate enugh to trigger the transistor/gate.

there are workarounds... the chip the gate comes on has 4 of them, with 2 chips you could have 8 gates. then you could divide the drivebay surface up into a grid, and have each small patch trigger a seprate gate. then you can hook all the outputs up to the same relay. you could do the same thing with transistors, it would take up more room tho.

often the easiest solution is to get a touch sensitive membraine, or make one. this is a lot simpler then youd think. you take 2 pieces of tin foil and a piece of ESD foam. you will also need some powederd graphite (soled as lubercant), and some overhead projector film. if you glue each piece of tinfoil to the overhead film's rough side, then cut it out to make 2 pieces 5.25" wide... then you get the ESD foam as thin as you can, and rub in lots of graphite. then you sandwich the foam inbetween the 2 tinfoil-plastic pieces, and glue around the edges. solder to each piece of tin foil, one side goes to + and the other to a comparitor. when the resistance drops below a pre-set threshold, the switch activates.

this works because when you touch the pad, the distance between the 2 pieces of tinfoil gets smaller, and a more direct path thrugh the graphite is made.

if you would like more detail on either method of touch switch, just let me know
 
You might want to look into these. I didn't see any information about plate size, but they look very flexible.
 
jpmkm said:
You might want to look into these. I didn't see any information about plate size, but they look very flexible.
Click to expand...

WOW these are capacitative touch switch chips, and will work in any applcation 1000x better then either method i posted above. and there increadbly cheap. i guess the days of the ghetto-modded touch switch are over, eh? exclent find jpmkm
 
Yep, only a few extra discrete parts are needed, plus an amplifier section if applicable. And DigiKey/Farnell has them, too.
 
btw, is that an old Forrest Mims engineer's mini-notebook? I think I have the same one. I love those things. :D
 
thx for the replies and info, but I think I'm gonna have to scrap the idea. I'm too new to electronics and this would be biting off more than I can chew, something I hate doing. Maybe if it decides to rain for a month :D
 
jpmkm said:
You might want to look into these. I didn't see any information about plate size, but they look very flexible.
Click to expand...

So it says it will easily detect through a dielectric, but if I connect the conductive door of my 6070 to it will it extend the sensative surface over the whole door, changing the front of my case into a sensor? My n00b knowledge of capacitence seems to think so, given that it will auto-calibrate, but I don't trust it enough to invest.
 
jpmkm said:
btw, is that an old Forrest Mims engineer's mini-notebook? I think I have the same one. I love those things. :D
Click to expand...
yes sir. god bless that guy. my uncle got me "getting started in electronics" when i was 6 or 7... ive been doing electronics ever sence.

DunM@ said:
So it says it will easily detect through a dielectric, but if I connect the conductive door of my 6070 to it will it extend the sensative surface over the whole door, changing the front of my case into a sensor? My n00b knowledge of capacitence seems to think so, given that it will auto-calibrate, but I don't trust it enough to invest.
Click to expand...

the bigger the conductive surface (not the dialectric) the less sensitive it will be. for example you may work perfectly fine with a finger on an acrylic coverd CD drive, but when you have that huge chunk of metal, you might need to use your whole hand. also if the door touches the rest of the case, it wont work at all because the case is grounded, and it specifyes that the conductive plate must float.

and why would you want the whole door a switch?
 
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