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Topic: Arduino as Capacitive Sensor (Read 29 times) previous topic - next topic

sillyrabbit

hey,

i'm trying to do the same. i was initally using the capsense code but abandoned it because i couldn't seem to create multiply capacitive sensors from it. i'm not that hardcore a programmer you see.

instead, i found this code http://www.arduino.cc/playground/Code/CapacitiveSensor

which works perfectly in arduino, the numbers are outputting and i'm trying to use with the arduino2max patch but no joy. as the pins are declared in the arduino code, surely the max patch should read the digital pins? any help is really appreciated.

Cheers

MiG

I'm currently building a capactive measurement system as part of my PHd, I've found, depending on what accuracy you want, that the best way is to use a sigma delta modulation technique. You can find this in Analog Devices AD774x series of Capacitive to Digital Converters. These chips go from one channel to 12 channels for mounting capacitive electrodes and have resolutions between 8 and 24 bits over full scale ranges of around 25pF with a bit of calibration, obviously, that gives a lot of sensitivity.

The chips communicate with a host through the i2c bus, so you ca use Arduino's wire library to get the data out of the slave chip (I sweated over a prototype function for a PIC i2c protocol for months when I found arduino!) and use that to manipulate the data anyway you want.

the only thing is that these chips are only available in TSSOP form so can be a bit of a pain in the arse to solder, however it's quite a nice solution as I am finding out.

ohnoezitasploded

What is the purpose of the guard pin (pin 10)?  The code seems to work just as well without it...

paulb

You are correct that the guard pin doesn't do much and can easily be omitted. This was a klugy way to implement a technique which is used with op amps and other high impedance (low current) circuits.

You can now use the [[http://www.arduino.cc/playground/Main/CapSense| capSense library]]  and use any pins you want. The results will vary a bit from pin to pin though.

But if you do want to make the wire insensitive and only the foil at the end sensitive, use shielded audio wire and ground the shield on the duino end only. (Make sure the shield on the other end doesn't touch the sensor, or it won't work.

Paul

dentrado

What is the difference between this and http://www.arduino.cc/playground/Code/CapacitiveSensor? Is the one wire method only for direct touch, while this can sense a longer distance?

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