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Author Topic: DIY Touch Sensor  (Read 4605 times)
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Hello all,

I've just read http://www.gogglemarks.net/index.php?action=display&tag=fightswitch, very interesting. Can someone please explain (parts ect.) how to make a simple capacitance sensor and hook it up to the Arduino?

Thanks,
Superware
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Daniel
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you can make your own sensor with a dozen or so parts, and fiddle with it forever to get it stable. Or, you can get QProx touch sensors...
This evaluation kit is a great way tio start. Digikey has them for about $20.

D
« Last Edit: December 30, 2006, 09:28:57 pm by Daniel » Logged

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This is not the same thing at all, but is a lot simpler:  you could just make a simple light sensor using a cadmium sulphide photoresistor in series with an ordinary resistor (I used 10K to make sure I wasn't wasting too much current).  Connect one side of the photoresistor to your +5V, the other side to the top of your ordinary resistor, and the bottom of your ordinary resistor to GND.  Attach the junction where the photoresistor connects to the ordinary resistor to one of your analog input pins.  What you have here is a basic voltage divider.  

The voltage received by the analog input pin increases when the light hitting the photoresistor is brighter, and decreases when the light is darker.  Now put a lamp where it shines on the photoresistor.  When you put your hand between the light and the photoresistor, the analog input pin can detect the shadow and react to it in some manner.  You will have to experiment using a voltmeter (or just printing sample values to the serial port) to figure out what your algorithmic thresholds should be.

Of course the behavior will depend on ambient light, so the program might get messed up if the Arduino board is near a window on a bright day, etc.  Not nearly as cool as that capacitance sensor, but hey, it's a LOT easier to build (or cheaper to buy, depending on how you look at it)!
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Qprox Capacitive Touch Sensors (includes code)
http://www.tigoe.net/pcomp/code/archives/arduino/000331.shtml
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Thank you all for replying... I know about Qprox products, but still want to know whether it's possible to make a simple sensor using simple components.
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here you can read how to do it...

http://www.bytecraft.com/touchsw.html


mind you a qprox sensor is a bit more reliable than this

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If you want a simple sensor that senses finger touch, here is another approach:

http://www.kpsec.freeuk.com/trancirc.htm

In the section "Darlington Pair", look at the schematic with the label "Touch switch circuit".  I have built these and they are surprisingly sensitive.  

The schematic says to use +9V, but I have used +5V and it works just fine.  Replace the 470-ohm resistor and the LED with a single 10K resistor, and attach the transistor collectors to one of your analog input pins.  

The voltage will be +5V when there is no touch, and will drop dramatically when you touch the sensor.  In fact, with some experimentation, you should be able to have your program react differently based on how much pressure you apply to the sensor.
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Great resource, but this has nothing to do with capacitance...  smiley
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Daniel
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Quote
I know about Qprox products, but still want to know whether it's possible to make a simple sensor using simple components.

sure, you can build your own capacitive touch sensor with discrete parts... but you'll need to amplify and condition the 'touch signal', and by the time you finish doing that, the Qprox individual sensor, at about $3 each, are infinitely simpler and infinitely more reliable!

http://www.edn.com/article/CA498777.html
http://amasci.com/emotor/chargdet.html

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