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demestav
Joined: 14 Jan 2008
Posts: 7
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 12 May 2008 9:47 Detect Simple Vibrations |
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Hello all,
I want to build a PIC based board to detect simple vibrations to be used as a switch.
My question concerns the sensor. I was told that I could use a buzzer to convert vibrations to voltage which the PIC can read.
It does sound reasonable as a buzzer takes voltage which is converted to vibrations and finally sound. So it will be this process reversed.
I would like to hear your more experienced opinion. Thank you.
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FvM
Joined: 22 Jan 2008
Posts: 2488
Helped: 409
Location: Bochum, Germany
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| 12 May 2008 18:38 Re: Detect Simple Vibrations |
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| Vibrations is a very general term. Depending on the frequency and amplitude, an electromagnetical or piezo buzzer transducer may be suitable as a vibration sensor respectively structural sound sensor or not. As an additional remark: An electromagnetical device usually would need a DC bias current to produce an output signal. Also acoustic guitar pick-ups could be used.
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demestav
Joined: 14 Jan 2008
Posts: 7
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| 12 May 2008 22:18 Re: Detect Simple Vibrations |
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Thanks for the reply.
Actually I want to create a simple drum pad. You hit it with a stick and the vibrations detected will generate (through the PIC) a logic signal.
So you think the buzzer will be enough?
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FvM
Joined: 22 Jan 2008
Posts: 2488
Helped: 409
Location: Bochum, Germany
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| 13 May 2008 0:01 Re: Detect Simple Vibrations |
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| I would expect a few 100 mV signal with an electromagnetic buzzer. I tested with a Hitpoint 5V AC PB1220PE05Q type. It seems to have a permanent magnet and thus produve output also without a bias current. Piezo transducers may probably give higher output, but I didn't have any at hand.
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demestav
Joined: 14 Jan 2008
Posts: 7
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| 13 May 2008 8:48 Re: Detect Simple Vibrations |
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| So what do you suggest to keep the 100mv long enough to detect it with the PIC?
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FvM
Joined: 22 Jan 2008
Posts: 2488
Helped: 409
Location: Bochum, Germany
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| 13 May 2008 9:01 Re: Detect Simple Vibrations |
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| The "100 mV" is typically a damped oszillation at the 2 kHz buzzer resonance. An amplifier (one transistor or OP) with a diode rectifier can make a suitable detection circuit. Measuring the rectified level with an AD would allow velocity sensitive operation.
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demestav
Joined: 14 Jan 2008
Posts: 7
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| 13 May 2008 9:37 Re: Detect Simple Vibrations |
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Excellent! Thanks! I understand what you are saying. I am not good at all with analogue electronics!
Another issue that arises it the timing. The pad is expected to get hit quickly. This means that I need to adjust the settling time of the pulse to be as short as possible but at the same time be detectable by the PIC. How do you think I can reduce/increase the settling time?
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