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Force sensing resistors officialy suck for lip sensing

for the last 18 months or so, I have been attempting to make FSR’s (force sensing resistors), the same pressure sensitive sensors I use for finger pressure sensing (the “keys”), as an inexpensive, easy to integrate lip pressure sensor.  until just recently, I believed that the error was in my design.  I thought that it was possibly the condensation of spit on the sensor which caused them to fail do often-usually within 2-3 weeks of continuous use. 

Picture 36so I spent the better part of a couple of months redesigning the mouthpiece to negate this possibility.  the latest oneplaced the FSR in a sealed space with a printed rubber gasket that also acted as a sort of “reed”.  pressure Picture 58applied to the top center of this reed-gasket would transfer this pressure through to the fsr.  the area underneath was, by design, completely free of any condensation.  only the transference of pressure from lip to plunger to reed gasket, made it through and this solution worked beautifully…for a time…

Picture 60in the last few days I started noticing that the sensitivity to lip pressure had begun to lessen more and more.  I believed this to be something loosening in my construction but decided to investigate it today and noticed that the FSR looked…flat.  yes, it is already flat, but there is a certain look they have when they have been pressed too hard for too long and upon connecting a fresh FSR to the circuit, my fears were confirmed; spit isnt the sulprit this time, but the sustained continuous pressure necessary for proper lip sensing.

what this tells me is that pressing an fsr continuously and strongly, as is necessary for lip sensing, will cause its eventual failure.  the ones for the fingers last much longer primarily, I now see, because I do not press them continuously and when I do it is at much lighter force than with the lip which must be pressed to a middle-range to center the pitch.  in this way, when I needs to pitch down, I must only relax my lip pressure a bit and if I want to pitch up, I increase it.

so, this presents an opportunity because, well, I’m me and I see opportunities in situations like this.  now, after fully exploring the FSR for lip sensing, and watching it fail, I will use a ratiometric hall effect sensor, which is tiny cheap sensor that sensing the intensity of magnetic fields.  when a magnet is moved close to the sensor, it changes the amount of voltage that is allowed through the circuit.  my previous wx5 wind controller used such a sensor as well and it was wildly precise.  And they are actually easier to find than FSRs and way cheaper- €1-2 as opposed to €5-10 for EACH fsr.  the primary benefits are

  • longer useful life
  • much more precise
  • I can still use the rubber reed-gasket design
  • hall effect sensors are much smaller (1/4 the size of a fingernail, avg.) so the mouthpiece will be much much smaller.

 

I will use another FSR this week for some playing I want to do this weekend to play thru some new hardware and software updates, but I hope the have the hall effect sensor integrated within the next few days.

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