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Thread: EWI mouthpiece with breath and bite (lip pressure) sensors

  1. #26
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    Don’t think LM358 is rail-to-rail, which is probably needed at 3.3V. Lots of options are, though.

  2. #27
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    Fair point Jonathan, I'm running 5v with a pull-up but at 3.3V it may not suffice.

    As a note on the optical method, I just found the service manual for the AE-10 online, it appears the cantilever bar is equipped with a tab that simply just sits on top of a reflective sensor (type KTIR0711S) which is much like this:

    https://coolcomponents.co.uk/product...ectance-sensor

    So, nowhere near as complex as I thought, and one point scored for an optical assembly in case the Hall Sensor does not work out. This system may not even need an amplifier as output swing is effectively a range between 0V to VIN (5V)

  3. #28
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    Took a while to arrive due to the delayed shipping these days, but I have tested the QTR-1A sensor.

    It works at either 3.3 or 5 volts and has no trouble providing full scale output with 2-3 mm movement depending on the height of the reed above the sensor and reflectivity of the reed surface. I am surprised at the sensitivity and no signal conditioning or amplifier would be needed.

    This will lend itself well to being inlayed into the mouthpiece beneath the reed and detect lip pressure movement.

    Click image for larger version. 

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    Last edited by JohnEVI; 09-24-2021 at 11:04 PM. Reason: photo

  4. #29
    Senior Member Davidelvig's Avatar
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    I've been using these sensors for a MIDI wind controller breath sensor. It has an appropriate pressure range and has been reliable.
    Sourcing was problematic last year - competing with ventilator makers for parts! It's analog, and I can read it as fast as I like. I average the sensed responses for a few samples to smooth the signal.
    (I use the RunningMedian library for the math).

    I'm interested to learn along with you about potential bite and/or lip-squeeze pressure solutions.

  5. #30
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    Looks like a good option!

    I am using an MPX5010 in my new EVI. The MPX2010 works just as well in this current one (and much cheaper) but it does need an op-amp for full output.

    I have made an optical joystick with these reflectance sensors to use in my new EVI project.
    I replaced the potentiometers in a playstation remote joystick with small vanes that move toward / away from the sensor and this has proven to be much better than using pots.

    Click image for larger version. 

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    Likewise, for the lip pressure sensor, testing shows this to be a viable, simple option. It will just reflect off the inside of the reed and
    return ample signal requiring minimal processing.

    It would be great to know more about your design!

    Last edited by JohnEVI; 10-05-2021 at 06:31 AM.

  6. #31
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    This makes me wonder if it would be possible to create an instrument that controls the pitch by mouth shape alone without using fingers. My finger coordination is not good at all, but I'm good at whistling precisely in tune.
    But I imagine such an instrument would require a reed with lots of movement freedom and I'm not sure how blowing into the pressure would work with mouth wide open Another option would be to use optical sensors that reflect from mouth cavity (KontinuumLab had one similar experiment), but it could be tricky to ensure accuracy and hygiene.

  7. #32
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    I imagine that would be pretty complex and you may end up some a sort of a theremin-like device. Could be a bit frustrating to play.. I made a midi theremin, and let me tell you they are a real challenge to play!

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