double tape

[prprog01]

I am building a MIDI Marimba using the inwards of a midi keyboard. The keyboard is touch sensitive by using 2 switches per note. I already have a basic/starting circuit that will mimic the 2 switches behavior. It detects how hard or soft the piezo sensor was hit. I attach the piezo sensor to a wooden bar. (Eventually I will have at least 3 octaves of these bars). Question: Based on your experience with eDrums - and because I don’t have too many piezos yet to experiment - where are the piezos more sensitive on the flat metal side or the crystal side? Do I mount them with double tape? Does the double tape must cover all the piezo area or should it be small just to make the piezo vibrate?

Thanks,

[bogiesbad]

You will have wires soldered to the ceramic side so mounting brass side down is a given.
As for vibration...I would start with double-stick tape...assuming you have no sensitivity adjustment you might have to isolate the piezo more with foam. I would also float the wood as on a real marimba to eliminate crosstalk. I don't think it matters if you stick all the brass...not just the center.

[cheapthrill]

A MIDI marimba? What a cool idea, I sure hope you will elaborate upon how you made it in the future!

[prprog01]

MIDI Marimba

Still working on the circuit/prototype, but as soon as I have a good working solution will let you all how it goes.

[JimFiore]

Memories flooding brain... so many years ago...

I was going to do what you described about 20 years ago. I never got around to it but I did make a number of e-pads long before things like the PD-7 were available. I tried lots of different stuff including plywood and plexiglass for bases, plus other stuff for the batter surface. Plywood is generally pretty good because you want something that is acoustically dead. You don't want it to resonate. You want a nice, short, repeatable trigger signal. If found that affixing the sensor to the underside (metal to wood) with silicone II was very effective (and you could squirt some on top to protect the wires and release physical strain). The problem is that the pad will be somewhat more sensitive in the area directly over the piezo. You can solve this problem by physically decoupling the sensor. One possibility is to make each bar out of two pieces. One of the pieces will have a hollow directly above where the piezo is mounted and the two halves are glued together. This way, there is no direct path into the piezo from a strike anywhere on the bar and you get nice consistent triggers. Also, you can finish the top piece so it actually looks something like a marimba (the only thing I dislike about my MalletKAT is that it looks so industrial- there's no aesthetic, great device though it is). An alternate route which I used with much success to make drum pads with roto-tom hardware is to make a wood base (the roto bolt screws into this). An aluminum plate is covered with 1/8" sheet gum rubber, the piezo is glued underneath with silicone, and a piece of 1/2" open cell foam rubber is placed between the metal plate and the base. Seal the sandwich with packing tape along the edges and you're good to go. Not very pretty, but I made a bunch of them when MIDI was new and played them until the TD-7 came out.

Oh yeah, in the pre-MIDI days I also made a touch-sensitive trigger circuit to drive an Oberheim DMX drum box. The prototype worked well enough. Before I could get it completed MIDI hit the scene. The next thing you know I had a JLCooper Drumslave driving an E-Mu SP-12 drum computer. Just last week the SP-12 was thrown away. It had been in storage for 15+ years and when I took it out, it just made weird popping and buzzing noises, and ignored the front panel buttons. No use in repairing it.