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Thread: Choosing parts for a musical instrument project

  1. #1
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    Choosing parts for a musical instrument project

    Hi, I'm looking to eventually build a musical instrument (similar to an accordion) using Teensy for sound synthesis and I'm figuring out which parts to use. Mono sound with 4-note polyphony would be sufficient, 8-note would be plenty. A few questions:

    1) what's the best way to use a battery to power a Teensy (along with the speaker) and make recharging easy? I see that Adafruit has a Featherwing adapter board with a charging circuit for a LiPoly battery, but that seems to be for Teensy 3.x, and I'm not sure about the x? I guess a rechargeable USB battery would work, but are there other choices?

    2) I'd like the sound to be played either through a speaker or through an headphone jack (not at the same time). It looks like the prop shield has an audio amplifier and the audio shield has an audio jack. What's a good way to get both?

    3) I suspect that a Teensy 4.0 has more processing power than I need, but the price is as good or better than the 3.x boards. Is there any reason not to get it? Longer battery life with a lower-power processor, perhaps?

  2. #2
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    Here is the charger I use with Teensy 3.6 and 4.0: https://www.adafruit.com/product/2124
    Battery I use: https://www.adafruit.com/product/2011
    I make something a little similar: QuantoGraph.com

    When I started something like you do, I've found that the good buttons are very hard to find.
    They are all too hard to press.
    I use capacitive sensors now, but they are no good for an accordion: you need to "feel" the button first, then press it.

    For the sound, either Teensy is good, but 4.0 will give you more power to make better sound. You just get a bigger battery for it, it will last for hours.

    For switching between the amp and the headphones, add a new phone jack with 5 contacts, which switched to the amp when the phones are not in. Use the 2 holes next to the on-board jack to connect the new output.

  3. #3
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    Yes, switches seem tricky. I'm thinking of using mechanical keyboard switches, but they are too large, since accordion buttons are closer together than keyboard buttons. Perhaps they can be cut down.

    Do you use the battery charger separately or is it part of your instrument?

  4. #4
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    The charger is integrated. It charges from the USB, just like your phone.
    The only thing I added is a 3 contact switch. In the Off position, it connects USB power to the VIN, as it did before you cut the bottom contacts. See the battery instructions for that.

  5. #5
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    I am not sure what you're saying about adding a new phone jack. Are you using the audio shield? What do you use for an amp? Are you replacing the existing stereo out connector?

  6. #6
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    For the amp, you need to find what you need. I used a very small one, to fit my instrument. For the accordion you need something loud, just mind the battery drain for it.

    For the headphones you have 2 options/
    1. Use the audio board's jack for the phones only and connect the amp to "Line out" pins on the board. You'll need a switch and volume pot for the amp. The phone jack will be always on.
    2. Don't use the board's phone jack at all. Get something like this: https://www.adafruit.com/product/1699. The pins in the back connect to the phones when they are plugged in or to each other when the plug is out. In this case the phone line from the board is connected to the amp, which you connect to the back pins of the jack.
    It's very simple when you get the external jack. The holes for the phone wires are on the edge of the board, right next to the phone jack.

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