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Filtering a pulse from a pizeoelectric sensor.

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LiquidOrb24

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I have an electric drum pad that has a piezoelectric sensor in it that outputs a voltage when hit with a drum stick. I put this through a few op-amps to increase the gain to drive a few LED's so that they light up when hit.

I need to now put this pulse into a PSoC microprocessor so that when the drum is hit it initiates a start sequence for something the processor will do later.

My problem is however that the signal isn't very clean and in fact has many oscillations in it and it looks like it will be very hard to use if I just want a clean pulse and for the interrupt to happen on the rise of each pulse.

My question finally is how would I filter this signal from the sensor so that it is a clean logic step signal or pulse so that when it goes into the PSoC it is almost as if hitting a button.

I don't know if a high or low pass filter would work or an A/D converter but I was hoping for something like a circuit or IC that would have a set threshold voltage so once it is passes by the hit of the drum another part of the circuit would send out an impulse or step.

Any idea would help

Thank you.
 
Actually, what you probably want is not so much a filter as a debouncer (a low-pass filter might smooth out the waveform but it won't sustain the waveform for you). You could use a 555 timer in the monostable circuit configuration to get it to light the LEDs for a certain amount of time (by controlling the capacitor charge resistance), and if you wish, with delays between successive lightings (by controlling capacitor discharge resistance) once the piezo passes a voltage threshold (which you cannot set due to the digital nature of the 555. You can however, use a simple voltage divider to scale the piezo voltage down and control the threshold indirectly that way. But the threshold probably isn't too important anyways in this case.

You wouldnt not need op-amps anymore if you did that unless you have too many LEDs. The 555 can be powered up to 15V so the voltage for LEDs should not be a problem.

You do not need an A/D converter if you just want thresholding (this is the case where you use a debouncer). If you actually need the analog output of a piezo, then you cannot use a debouncer. You must use a LPF, amplifier if needed, and ADC.

Analog or digital, you want some clamp diodes on the piezo output. since it can easily exceed 50V, and even 100V if deformed quickly enough.
 
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