Capacitance sensor guide (AD7746)

capacitive_sensor

[Marcus] has written up his experiences using the AD7746 capacitance sensor. He used the SparkFun breakout board in conjunction with an Arduino. The available Arduino code wasn’t that great so he rewrote it to be easier to understand. The AD7746 is an I2C device that can be continuously read, but this doesn’t mesh well with the Wiring libraries. Additionally, the calibration routine from the data sheet is difficult to understand. He’s included all of the code he used plus a Processing sketch to help visualize the input which will hopefully make your experience with the chip much more smooth.

Comments

  1. therian says:

    the cheaper way of doing is is transistor oscillator small capacitor and diode. or with little hacking single micro controller can handle this by it self

  2. threepointone says:

    i’ve used the ad7746 before, and I can tell you that you can’t get the kind of performance you see in the 7746 with a simple transistor oscillator or a little microcontroller. you can measure ridiculously small capacitances with this guy if you implement it properly.

  3. therian says:

    I think I just too cheep when it
    coming to parts, 90% of my parts coming from old VCR players and stereo

  4. jproach says:

    Yeah I’m not quite sure why anyone would use a $9 IC as just a touch sensor. There are many simpler and better options out there for button touch interfaces (or even scroll wheels, sliders, etc.). But I guess its a first step.

    For a basic touch only option, check out the Qtouch chips and AVR Qtouch library.

    Some cool things that the AD7746 could be used for: non-intrusive liquid level measurement, flow rate, various strain applications (pressure, weight), humidity sensing, etc.

  5. svofski says:

    I made a capacitive sensor matrix 4×3 with little more than atmega8 and some caps. The performance you get with a micro is enough. These sensors are probably designed for something more sophisticated.

  6. lekernel says:

    is there a life beyond arduino, adafruit industries and sparkfun?

  7. Dan says:

    @lekernel

    Yep. It’s called Digikey. A lot cheaper too, but perhaps too scary for most people.

  8. entropia says:

    @lekernel

    yeah, i’m getting tired of the arduinoaday.com too.

  9. googfan says:

    You cant use this near rf sources, it goes crazy.

  10. tantris says:

    Have a look at AD7147 and AD7150:

    Cheaper ($3-$4), and AD7147 supports several input channels.Unfortunately they come in really tiny packages. Hard to make your own breakout board with these tiny leads.

    Ironically, AD7746 is available as MSOP. You can solder it to a normal prototyping stripboard if you cut the stripes on the board in half.

  11. Agent420 says:

    I used touchpads from scrapped laptops for touch sensors before with an avr… works great, much cheaper.

    http://forums.bit-tech.net/showthread.php?t=112110

  12. lekernel says:

    sure, and more interesting than arduino self-proclaimed “hacks”, but hey, it’s not what the masses like.

  13. Bob says:

    My gawd! $24.95 to sense touch? OUCH!!!

    Whatever happened to the cheap $0.05 solution of using a resistor and capacitor pair tied to a port pin along with some simple code for sensing finger proximity? (OK… more like $1.50 at your neighborhood Sh!tShack store with their 3000% mark-up of repackaged surplus.)

    Even a hard to find, overpriced, $3-$6 QT113G chip still needs a capacitor wired to it?

    #2 (old school)engineering rule:
    K.I.S.S – Keep It Simple Stupid

  14. robmora says:

    @ dan:
    Digi-key cheap? I suppose it’s all relative, as with everything else. (I still loves me my Digi-key however).

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