so, watching sam’s videos about synth bike 3, and how he used the wav trigger for drums, inspired me to start using them for work! i’ve built several things with WAV triggers inside them - the only one i have photo/video of at the moment is the “walk-on piano”. yes, like the one from the movie. (for context - i work as a technician at a science/children’s museum.)
mine uses two WAV triggers (17 notes!!! had to buy a second board…) and the pins are connected to this stuff called “low-profile strip switch”, US brand name Tapeswitch ( link ). it’s intended for use in factories with big machinery, so that if you step on the strip or pad, the machine stops before you die. OR, if you step OFF the switch, the machine stops because you walked away.
and jesus it’s expensive. 50 feet is just over US $700. but it needs to last “forever”, with hundreds of people jumping on it as hard as they possibly can with their full body weight, for 8 hours a day every day of the week. and it’s the only thing i’ve found that will take it for more than a few weeks (the previous one lasted just under 15 years).
the bottom is just a sheet of MDF, and the graphic is CNC’d second-surface-print 1/4" polycarbonate. second-surface means that you flip the graphic and print it on the reverse side of the material, so that it’s protected when the front surface inevitably gets beaten on and scratched to hell. the poly just slots between the MDF and a piece of aluminum corner trim and is held in place by gravity.
the thing is crazy popular! kids love making noise. older kids love showing off what they’ve learned in piano lessons (mostly Fur Elise). adults love to try all sorts of stuff. i think my favorite is when i heard the distinct melody of tchaikovsky’s 1812 Overture coming from behind my office door.
Finally, something with controls spaced appropriately apart for performance gigs!
That’s an amazing thing you made and it sounds like it is well loved.
If you wanted new sensors, you could experiment with capacitive sensors that detect proximity. It’s cheap and just a wire will work but it is not pressure sensitive. Arduino has a cap sense library that works ok.
Or you could use piezo strips which are a little hard to drive but once you get the circuit working, it is not too hard. The circuit values have to change with the length of the strip. We used 1m strips. They are not inexpensive though.
I would love to see more (pics schematic etc) on your use of these piezo strips.
I have used various piezo forms for pickups for audio and triggers but I’ve never used these strip ones (usually used in buildings). Any and all info on driving these would be appreciated.
Can you ‘drive’ the strips like a speaker driver?
The strips I used looked just like the picture and were 1m long. The picture is from Digikey, TE Connectivity makes them. They are a “constant charge” device so if you squeeze or flex the strip, the voltage goes up. It goes up high enough that if an NE2 bulb is connected to the terminals, it will flash when you flip it back and forth although you cannot feel it if you touch it. The samples I had were super thin and flimsy like a candy wrapper and they can wrinkle easily. That does not hurt them too much though. They do not degrade if they get wet like the resistive strips (FSR). They cannot really wear out like the resistive strips either.
The correct sensor receiver is an integrator and the integrating capacitor has to be a ratio of the sensor capacitance to match the gain of the amplifier. Otherwise the bandwidth gets wonky and it is hard to tell what you are sensing. Voltage mode does not work that well and is less sensitive than charge mode. I may have an old schematic. TE Connectivity has good resources too and they were a big help during the design.
I don’t think they will drive well, they are really flimsy but maybe with a really high voltage source and a firm backing they would do OK. They were not super easy to work with but for the right application, they are the only thing.
Thank you for the details and the info.
Like @Bitnik you’ve kindled a greater interest in this type of piezo.
I’ve been looking for suppliers of the little chip piezo pieces that are used in under saddle guitar pickups and also the “rope” type but like the round discs I use on homemade instruments the minute you add any mention of music to your search the price doubles.
I built a hexaphonic pickup for an old half size hohner electric to see if I could make a MIDI/ analogue controller and used the piezo chips from a dissected under bridge pickup but the maths was beyond me for getting a workable and adjustable response. … and then i got ill.
I did stick a piezo under the bone bridge of a sitar and passed different notes through it to make a drone. (Loved the idea but it sounded like reversing a truck over a bee hive).
What is the ‘go to’ resource for piezo electronics?
Thanks again @feralbeagle. Any photos of your projects?
how do you think these strips would hold up to 10 to 15 full grown adults (250-300lbs. or 113-136kg each) jumping down on them with their full body weight as hard as they possibly can, constantly, for 8 hours a day, every day, forever?
that’s the reality of the use-and-abuse that i have to build for at work
If you can manage the impact force (say on the underside of a plate). I’d imagine you could have a coach load of people dancing on this for years.
An architect pal told me they can use the strips in concrete to test for stress.
(That said. I’ve no first hand experience… yet)
that’s good to know. the tapeswitch material i used can also hold up for years and years, so it’s nice to know that there is at least one alternative out there!
I’ve used a pressure switch and a sealed garden hose pipe to make a switch, much like the old 'ding‘ line they used to lay across garage forecourts to let owners know a car has arrived.
It’s another way to go.
Remember when they used to have a pressure line in the road to operate some light controlled junctions? I saw a burst one once. It looked like a strip of vulcanised rubber hose embedded in the road, with some metal casing for protection. Once I saw it the purpose was easy to deduce. This would have been forty or fifty years ago
They still use them for auditing traffic volume. Its a loop of hose back to a pressure sensor. Id love to find one of the old boxes with the paper reel and pen marker machine (sure there’s a propper name for them but its playing truant from my brain)
It would take some experimenting with rubber mats but it would probably work. You can look at the less sensitive FSR strips too. They wear out after a lot of use but they are less expensive and much easier to connect to something like an arduino.
Here is an example circuit for piezo strips from analog semi. R3 is there for a DC path so that the op-amp does not get stuck the rail. The gain is the C2/Cs ratio if I remember correctly.
