[jerb]

hey there, I'm looking for the name of a chip, I dont know if you can help but if any one has any idea where to start it would help. I seem to remember a thread a long way back talking about these chips but I cant find it anymore.

I'm looking for a capacitance sensing IC, or atleast I believe thats what its called. Basically What I need it to do is read changes in a field around it, if I move my hand closer or farther away it will vary its output to control a light or change volume. any idea where I should start looking for this or what they'd be called?

 

[Porksoda]

I think you could do something like this with a 555 timer. In a simple square wave generator configuration, as the capacitance varies the frequency of the square wave output would vary (higher capacitance = lower frequency). Or, possibly if you get sneaky you could get it to vary the duty cycle with capacitance. In the case of the first one, you could hook it up to a frequency to voltage converter, and that should more or less give you what you want. If you can get it to vary duty cycle, a simple low pass filter on the output would get you the voltage output you seek.

I would offer a more specific description but I haven't worked with 555 timers in a while and I am feeling lazy.

Perhaps I will play around with a circuit later if I get bored

Have you considered different ways of sensing distance? One that a prof of mine used to great success is to shine an LED at the surface you are ranging, then point a photoresistor at the spot of light it makes. As it gets farther away, the intensity of the spot decreases, and the resistance varies. Set up a simple voltage divider and an op amp to amplify and buffer the signal, and you are set!

 

[threepointone]

there's a bunch of stuff on mouser, just look up proximity sensor. if you have their catalog, it's on around page 1401.
The inductive sensors seem to be what you're talking about, although they look pretty darn expensive.

this might be an alternative:
http://www.hackaday.com/entry/1234000873073550/

I just looked up capacitive sensors at mouser--they seem to be different from inductive sensors, and a lot more expensive. I don't know what the difference, though.

 

[AtomBoy]

It sounds like you're looking for a QTouch chip from QProx:

http://www.qprox.com/products/index.php

I have had a QT411 for a few months with the idea I'd make a volume control. I'm still in the research phase- reading PIC literature.

 

[jerb]

thanks for the responses guys, So far I like Porksoda's Idea best.

I had checked mouser but most of the offerings dont fit my application, the data sheets all say they can read the proximity of a metal object.

I say the Qprox on a google search but there wasnt that much on their uses, they seemd to be actionless switches by the looks of it, will they work for my application?



what I would like to do is mount one of these things into my desk so I can vary the intensity of a lamp by moving my hand up and down (very simmilar to the mathmos Airswitch)

 

[jerb]

WOW! I followed the link about using LED's to sense proximity... Thats AMAZING!!

I took a random red LED I had lying around, hooked it up to a very cheap DMM and held it to the light and BOOM I saw 20 mV appear! thats incredibly cool

EDIT: I got 120 mV off a yellow LED

 

[Alwynjones]

I was trying to understand the working of capacitive sensors and came to know that they are capable of detecting metal and non metals. I have a question here, are all type of sensors do the same or they have different working principles?