touch detection

Hi,

Recently i got to see a post on "Simple One-Wire Touch Detector" - http://www.extremecircuits.net/2010/05/simple-one-wire-touch-detector.html. As i was seeing this, I got a question/thought/some thing like that. Which goes like this...

In the above mentioned example, if some one touches metal plate LED glows. Now my question is, if i have more than one such circuits, placed on same body, none of the LED should glow. Can it be done in some way? please help me out. eagerly waiting for solutions.

Thanks,
Viswanath

Are you just looking to have more than one metal plate for the purpose of additional inputs? If so, then just replicate the circuit "x" time for each plate in your design.

Also, there are many off-the-shelf capacitance touch sensors on the market that will likely provide better results than this circuit.

See: http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2557134&k=capacitive touch sensor

Hi Joe,

Thanks a lot for your reply. No, I am not looking for additional inputs for a same device. Rather, what i wanted is: say i have 2 devices of this kind (which detect touch and does dome functionality. Say, glowing of LED). Now, if i touch those 2 devices with two fingers both the LEDs on both the devices glow. Is it not?

What I wanted is, this should not happen. If a same person touches more than one devices at any given point of time. None of then should glow.

If you want more clarity, please let me know your email ID, I can explain you more clearly.

In that case, an interesting but bulky circuit will be to have the output of the first metal plate touched activate a relay to switch off other plates from source or from some other part of the circuit; Another less buçlky solution will be to use a micro-controller and make good use of your OR operator in programming it if you are using a high level language to program.

Hi Khaba bulu, Thanks for your suggestion. can you explain it more clearly?

see, for more clarity let me explain you in other way. say I embedded this circuit in a watch(metallic bottom) with LED in it. so,according to his circuit logic, as soon as i tie it to my hand, LED should glow. Is it not?

Now, my question is, if i have n number of watches tied may be to same hand or to different hands or may be one may tie to leg also. if more then one such watch is tied to same body, none of them should work. (caution: always there is a chance that no two watches touch each other). And if they are tied to different people, even though all of them are side by side. All of them should work as it is.

please think and let me know, if you have any solution for this....

Now I understand better what you want to do. Well the solution I will offer you now is not tested but you'll maybe test it and give a feedback.
1- Equip each of your watches with a Touch plate sensor to "ON" the LED as you normally intended to do.

2- Since the watches might be placed close to each other, put a proximity detector in each watch. your proximity detector should take into consideration the texture of the watches, and it should be placed at the right of the watch(where the time adjustment knob is normally located); so that when you put many watches on one hand, the first watch does not detect any object but each other watch on the same arm detects the one before it.

3- On detection, the proximity detector circuit should be able to disable the switching "ON" of the LED in the watch where detection occurred. If you can implement this, I believe it will solve the problem as you explained it.

Hi, I very much appreciate your efforts to help me. But, your latest solution seem to have some flaws. Like,

1) For example if i place one watch on one hand and another to my leg. still it should not glow as per requirement. But it will not!

2) let us consider, we used proximity detector. now i tie a watch and you tie another watch. And both of them will glow. is it not? now, if we bring both of our hands very close to each other, because of proximity detector, LEDs stop glowing.

So.... I think we need to have some more better solution. Can you please think more on it? by the way if you can give me contact detail like, email or mobile number. We can discuss more clearly.

Thanks once again...!

I think e-mail will be better because I notice from your name that you might be in Asia, meaning I am very far from you since I am in Africa. kbulu(_at_)yahoo.com , just mail me a better description of what you want to do, and don't forget; there is a difference between design, Implementation and construction. In each of the last two mentioned exercises, you'll notice that you might have to modify your design to meet up with some feasibility constraints.

Hi, I am not able to get your mailid. so. this is my id. Please send a test mail to it. viswanath.malepati(_at_)gmail.com

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