"Wireless" input device -- a virtural LaunchPad project

Sounds like an interesting / fun sensor project idea.  Check out slaa363a which is about MSP430 based capacitive signal sensing either using the comparator models or using general purpose inputs and I suspect your sensor might be able to be implemented in a similar fashion.  The capacitive sensing is probably going to be at best proportional to the area of the 'plates' which might be modestly large from the sound of your mentioning a can lid, but the factors that would cut that down might be an increased closest required approach distance in your design if you wanted to sense beyond 1mm or so travel distance, and the possibility that your bipolar / dipolar design might be less effective at generating capacitance variances than the scenarios mentioned in the app note which uses a ground ring in proximity to a central sensor.

ESD and EMI pickup would be a concern so I suppose you'd want to add some TVS type low capacitance protection and see if you can design the thing to minimize EMI pickup and yet be sensitive to the small capacitance signals. 

Using a piezo disc or film type pickup could also work well.

OCY,

Cool idea. Question for you. The sounds you would pick up from the castanuela would be just sound spikes, correct? or are you trying to also recognize like, grinding, or sounds other than just the click they make?

I have a few observations that might help, maybe not though. From my research and experience in medical sensing, if you plan on amplifying a capacitive sensor your amplifier should have a super high input resistance. Also, as far as picking up noise, you can just throw in a simple passive filter to filter out the noise.  A highpass filter would take care of most EMI, but it all depends on how much you are amplifying the signal from the microphone (if at all).

I also would suggest using as much analogue filtering of the signal as possible so that only desired sounds would trigger the comparator. This would make the simple pattern recognition fairly simple, and definitely would fit within the 2KB of flash.  I would imagine that it would consist of measuring the time between clicks and the duration of the sound?

Best of luck with the project. Sounds very cool!

-NJC

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Hayes and NJC,

Thank you both for the suggestions and encouragements.

I was think of a capacitive-mic-like device, not a real mic. I hope to be able to design it to pick up the clicking peaks from the castanuela but somewhat immune to other sounds, vibrations, ESI, etc. In other word, I want it to act like a mechanical filter/amplifier to selectively picking up the clicks. As for electronics, I intend to connect it to CA0, CA1 or CA2 of the G2211 with no other external components. The CA+ peripheral can generate 0.5*Vcc internally. It can be programmed to apply that voltage to CA0, CA1, or CA2 pin. It can then disconnect that and compare the voltage on that pin with the 0.5*Vcc. The leakage is small. If the capacitor decreases due to mechanical vibration, the voltage will increase above 0.5*Vcc. If the capacitor increases, the voltage will decrease. Discharge due to leakage will also decrease the voltage. But the firmware can periodically go through charge-compare cycle again. I was hoping that I can detect the rhythm of the clicks and use some particular patterns of the rhythm as input messages. (Not Morse Code, but that is where the idea comes from.)

I admit that this is really crazy.

--OCY

When you got it working, you can 'upgrade' it to a glass-breaking sensor: signal an intruder alarm if you hear the glass of the window being shattered.