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Thread: YATB - Yet Another Teensy Board :D

  1. #101

    Re: YATB - Yet Another Teensy Board :D

    Driving it directly with an output pin seems dangerous!
    A sharp kick to the board can easily generate 10V or more of piezo spiking.
    The resistor doesn't really drop voltage; rather it limits current; high voltage may end up punching holes through the driver FETs on the output pin (avalanche) and burn it.
    The pins are often protected with some kind of Zener for ESD purposes, but those Zeners have very low current tolerance and may burn out, too, after which the output pin is entirely unprotected.
    An external Zener clamping at 3.6V and rated for 100 mA or more would probably be a good idea!

    Separately, when you turn off the unit, it will still have energy that needs to be dissipated, and if current goes down, voltage will go up!
    Thus, I typically parallel these units with a 1 kOhm resistor, and additionally add a low-voltage Schottky diode in parallel, reverse biased. That makes sure I can on/off the unit with reasonable safety.
    Then again, I usually drive them with square waves, and a separate switching transistor (BS170 or simliar) which doesn't allow high quality audio signals. (The frequency response of these buzzers is typically tuned for a specific frequency anyway.)

  2. #102

    Re: YATB - Yet Another Teensy Board :D

    Actually I am using a small Mono Amp chip (LM4862 chip) to drive a small speaker. I have one IO pin D4 which is used to enable or disable the sound and it gets the sound from the DAC pin. So if I want I can use the Audio library and/or I have tried out Talkie code before...

    I have not tested this part of this board out yet...

    Spent some of this morning replacing my Iphone5 which fell into toilet on Saturday with new Iphone7 :0 So still in process of setting that one up. I might have been able to resurrect the IP5, as some of it still worked, but the touch screen did not so I could not quickly turn it off and it drained a half charged battery in probably less than an hour.... So even if I could get the screen to work, not sure I would have trusted it without at least replacing the battery.... But I am totally off topic

  3. #103
    Join Date
    May 2016
    White Plains, NY
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    Re: YATB - Yet Another Teensy Board :D

    Oh, Jeez! I'm glad I asked! I hadn't considered that effect. I won't populate the buzzer.

    I do like audio feedback (pardon the pun!), so I'll add your suggestions to my newly-formed list of upgrades-needed-in-the-next-revision-of-copper. Hopefully that will be a while - I did remember to re-pour the power planes this time!

    There should be a web list of "Things that fell into the toilet!". I'd have a few entries for it!

  4. #104
    Join Date
    Sep 2010
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    Re: YATB - Yet Another Teensy Board :D

    When it is a plain piezo buzzer element without any internal driver electronics, the simplest method to drive it is to connect one lead to a power supply and the other to a low-side switch (e.g. N-channel MOSFET) that is controlled by a uC pin. You also need to add a 1k resistor in parallel with the piezo leads to permit charge/discharge of the piezo element. Applying a DC voltage to a piezo for extended periods (years) can cause chemical migration within the crystal, so simpler is not always more reliable.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  5. #105

    Re: YATB - Yet Another Teensy Board :D

    I, too, like sound feedback! Like Tician, I drive it with an N-channel MOSFET, and a 1k resistor, although I also add a reverse biased diode, for good measure.

    Kurt, that speaker is the cutest thing. So adorable!

  6. #106

    Re: YATB - Yet Another Teensy Board :D


    Yes before I was using these little AMPS, I have played around with some different buzzer setups.
    Most of them were copied from what I used on botboarduino (Atmega328) which was the same setup as was used on the old Lynxmotion Botboard2...

    Which I typically did something like go from IO pin through 4.66K resistor to Transistor to speaker, to +5v through 50 resistor, and also used a diode...

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