Xan's Pad Sensor Construction...

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Making a drum pad sensor is the easiest part of any of the pad projects contained in this E-Kit project...in fact, making the sensors are also the most fun!

First, let's look at what a piezo element actually looks like:

As you can see, it looks like a little brass disk with a ceramic disk attatched to it, with a thin layer of metal that has a wire soldered to it...and another wire soldered to the brass disk. (You can also get piezos without the leads, tho please try to get them with the leads as it's a real pain in the brain to attach your own leads)

Where to get these little monsters? Digi-Key finally has them, WITH the leads already attatched, for really sweet prices!

If the ones you have look like this:
Feedback Type Piezo

..then be prepared to have nothing but headaches unless you are willing to design a feedback circut to avoid false triggering and such...these types are better suited for other things.

For best results, a piezo with an overall diameter of one inch (25.4mm) or larger will do just fine, if you can get larger, go for it, just remember that some of the pads in this project require more than one cookie-cutter size of element.

To start with, I like to add custom Internal Connectors to the ends of the leads, the details I've placed here - Internal Connector Details - This should make more sense!

Why do we want to use internal connectors like this? Simple, if it is needed, you are able to remove this sensor assembly and replace it when the pad wears out, or the piezo becomes damaged...most likely the pad will wear out ages before the piezo gets damaged...this is just an ounce of prevention in the long run, you'll thank yourself for doing this when the time comes.

Next, after you have prepared all of the piezo elements with these custom connectors, it's time to prepare the plates they will be mounted (permanently) to...the best method for preparation of the sensor plates (after cutting them out) is to file, grind or sand the edges smooth and rounded, see Pad Construction Details for more depth...it also wouldn't hurt to use a swab and some rubbing alcohol or tape head cleaner (isopropyl alcohol) on the plain brass side of the piezo element just prior to assembly, to remove dust, fingerprints and other contaminates.

Okay, you have your piezos all set up, and your plates all prepared, now it's time to get into the fun stuff...make sure your plates are clearly marked where the piezo will go, as well as the ground wire (you DID add a connector to the ground wire the same length as the piezo wires, didn't you?), and get out your hot glue gun or mix up that epoxy, and smear some of the adhesive to the back (the brass side) of the piezo elements like so:

Piezo and Glue

And then attatch the piezo to the prepared sensor plate, and press firmly, then put some weight (like wax paper, a coin and a heavy book) on top of the piezo CAREFULLY, and let them sit at least overnight until the piezo is completely dry and attatched permanently to the sensor plate(s).

Your finished step should look similar to this:

Piezo on Plate

(Note that the ground wire in this picture isn't placed, and that the sensor plate may not always be round...)

Why a ground wire? I am a truly anal perfectionist, and the finished pad should be compatible with ANY module, meaning you will have option of polarity of the piezo with a respect to ground, and a metal shield to lower any occurance of RFI (Radio Frequency Interference) that may occur in a live gig situation and cause false triggering...consider this just another ounce of prevention in this method of construction ;)

It also wouldn't hurt to give the piezo a light coat of clear enamel to avoid oxidation.

Okay, after the plate and piezo assemblies have slept well (glue has dried and set), it is time to prepare the encasement of the sensor plate assembly into a mousepad sandwich...you can find rolls of mousepad material at Ledge Hill Advertising, unless I find a better source...they also have wristpad material as well, which has given me plenty of ideas for some interesting triggers, as well...

Be sure to make two identical shapes of mousepad for the top and bottom, giving about a quarter-inch (6mm) from the edge of the sensor plate, and an additional quarter-inch (6mm) for the mounting into the pad shell...the thickness of the material should be 1/4 inch (6mm) to start with, to give the pad a bit of a 'pudge' when mounted to the rest of the pad assembly...oh, and important, the cloth covered color side should be on the outside, both top and bottom, even if it has no cloth backing, in your choice of color...avoid the plastic-coated top shit, you want the cloth topped, as it will last longer...keeping an old toothbrush (or three) and foaming upholstery cleaner in your emergency bag will keep them looking pretty, and cleaning regularly will alert you to when it's time to replace the pad material.

Another way to extend the life of the pads is to purchase self-stick drum dots and put them in the center or directly over the piezo area...this -will- add stick noise, of course, but these pads are not intended for keeping the neighbors happy, they are intended for clubs and bars and other gigs, where the only reason you need to wear headphones is to make sure you will still be able to hear the next morning :)

Here's a diagram:

Sensor Diagram 1

When assembling the two pads to the sensor plate, first secure the plate to the top pad with a couple of drops of super glue (USE SPARINGLY, you'll want to remove the pad later for replacement), and then to the other side as well...then secure the two pads together with hot glue or some other permanent adhesive, avoiding getting any on the sensor plate so you will be able to tear the pads off from the plate for replacement (you DID thread the wires through the slit, didn't you?!?), and then again place wax paper and a heavy book on this assembly overnight to make sure it remains secure.

Here's another diagram:

Sensor Diagram 2

(Wouldn't it be nice to have x-ray vision?!? *laugh*)

And another diagram:

Completed Sensor

Again, please note that not all sensor assemblies will be ROUND!!!

Addendum: Be it known that the two-piece pad construction above may not apply to all the pads in this project, as they may be of the type to have edge-triggering ability and therefore will be a one-piece folded over the sensor plate...more details once you encounter them.