The piezo sensor, or transducer, is the component that makes the whole thing tick. It detects vibrations resulting from a drum strike and converts the force into a voltage that is linear to the force of the strike. This is due to the unique electrical properties of quartz. Quartz vibrates When an electrical current is applied to it. Watches exploit this property to effect movement, and buzzers also work on this principle. The interesting thing is that the opposite is also true - when quartz vibrates it generates an electric charge.
Most sites that I've seen use the venerable model #273-073 from Radio Shack for the piezoelectronic element. You pretty much break the plastic casing with a pocket knife, then pry the element out, hopefully without breaking it. I've had luck doing this, but have broken a couple elements too. I highly recommend buying piezo elements directly from Digikey, as you don't have to do surgery on plastic and they cost half as much as the Radio Shack version. Just search for "piezo element" and you'll see many options for around $1. I believe the ones that I used were 27 to 30 mm, 2.5 to 2.6 khz. They didn't come with leads, but I was able to solder one wire to the quartz (middle) part, and one to the metal substrate. The solder doesn't stick too well to the quartz, so I added some epoxy after I soldered to make sure the wires stayed put.
The elements are very sensitive to the touch, and will generate voltages that far exceed the 5 volt reference voltage of the pic. Thus, a voltage divider circuit is necessary to scale the voltage down to a manageable level. For the sensor alone, a voltage divider using a 4.7k and 1k resistor will bring it down to a good level. See the picture below:
One thing to note is that once you attach this to the drum unit, the amount of vibration that gets transferred to the piezo element is reduced greatly. For example, the voltage divider circuit I used for my drums had the resistors reversed so that the voltage is only slightly moderated, as shown below:
The piezo transducers will be soldered to the bottom of the drums, which I'll get to in a bit.
Now to Step 2 - building the drum pads.
Home
Step 1 - Building piezo sensors - the heart of the sensor - transforms vibrations from the drum strike into voltage which varies based on the intensity
Step 2 - Building drums - my design uses gum rubber epoxied to thin plywood
Step 3 - Building the case - holds the drums and electronics, also isolates the drums from each other - UNDER CONSTRUCTION
Step 4 - 16F690 firmware description - UNDER CONSTRUCTION
Step 5 - Circuit design - UNDER CONSTRUCTION
Step 6 - Putting it all together - UNDER CONSTRUCTION
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