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Thread: Teensy 4.0 on lipo battery with DOG LCD guidance

  1. #1
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    Teensy 4.0 on lipo battery with DOG LCD guidance

    Hi,

    I'm looking to create a portable project running on a LiPo battery. 3.7v

    I bought a dog lcd with backlight and the docs mention adding resistors and capacitators when running on 3V.

    If I hook it up to a 3.7 volt battery, will 5V output from the Teensy still be giving 5V? I'm asking since I believe that powering the LCD from 5V is the easiest option. Looking at this post: https://www.pjrc.com/teensy/td_libs_DogLcd.html I would just need 1 resistor and I could run rest of my circuit on 3V. If I power it on 3V I will need capacitors etc I least that's what I gather from
    https://www.lcd-module.com/fileadmin...oma/dog-me.pdf I have the SPI model

    I guess I'm just asking here if these assumptions correct:

    - DOG LCD is easiest to setup with 5V power, just one resistor needed
    - A Lipo 3.7V powered teensy 4.0 can power an LCD at 5V
    - The SPI can at the same timer be operated at 3V

    Jeroen
    Last edited by Jeroen; 03-25-2021 at 09:57 PM.

  2. #2
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    @Jeroen:

    If it works for your project, I would recommend that you look into the Adafruit <2500 mAh battery>+ Adafruit <Powerboost 1000>. With this combo, the updated version of my <TeensyMIDIPolySynth> project (Teensy 4.1 + PJRC Audio Adapter + RA8875 7" TFT display, all running from 5VDC) operates either stand-alone, or with standard USB 5VDC input (which could also recharge the battery). Using the 2500 mAh battery, I can get up to 8 hours of operation, which was great. I've since moved up to the Adafruit <6600 mAh battery> for even more extended operations without any worry of exceeding the battery capacity. The Powerboost 1000 takes care of creating the 5VDC supply, charging the battery, & preventing over-discharge of the battery. If you have the room, including this combo into your project is well worth the minor additional cost.

    Mark J Culross
    KD5RXT

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    Hi Mark,

    I was thinking about this setup: https://learn.adafruit.com/assets/28039

    But I take it from your answer that I won't be able to hook up the LCD to 5V when running the rest on 3V?

    Space is somewhat scarce but it's good to know about te powerboost you mentioned.

    I think I will try running everything off 3V first and see how that goes.

  4. #4
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    Quote Originally Posted by Jeroen View Post
    But I take it from your answer that I won't be able to hook up the LCD to 5V when running the rest on 3V?
    @Jeroen:

    The Teensy 4.0 is not 5V tolerant, so running the display from a higher voltage than the Teensy runs the real risk of damage to the Teensy. Much better to run both from the same supply, whatever you choose.

    Mark J Culross
    KD5RXT

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    Hi Mark,

    OK I stepped away from the LCD for a bit. I ordered the 5V booster/charger you suggested but in the meanwhile I hooked up my audio project to https://www.adafruit.com/product/2124 and a 1200MaH LiPo. It works but and can work off batteries which is very cool but....

    My sound quality went waaaay south. Lot's of noise / static. The sound is fine if I plug headphones straight into to Audio Shield, but if I attach speaker(s) via a 6W or 3W amp it does not sound good. Not on USB power and certainly not on battery only, then it even just restarts the board sometimes.

    Interestingly the quality did get somewhat better after a clocked my Teensy down all the way to the lowest MHz. Before that the board would always just restart itself after turning the AMP on.

    I checked the amps voltage, it gets 3.3V.

    Any ideas here? Does this simply mean my project is underpowered? I don't understand the difference in before and after my battery circuit implementation. Running off USB should yield the same results, but it does not. It's much worse now than before.

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    I am not familiar with that particular adafruit product, but is appears to be a battery charger only . . . it does not provide a regulated DC output for powering devices like the Powerboost 1000C. Based upon your description of the Teensy resetting when the amp is powered on, my uneducated guess would be that all of your devices combined (Teensy + audio + charging battery) are probably pulling more current than your USB can provide. If this is truly what you are experiencing, then slowing down the Teensy would certainly reduce the amount of current that it requires. As for the noise, the charging waveform is probably leaking into your audio somewhere/somehow . . . again, just a guess.

    Mark J Culross
    KD5RXT

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    Wel it was designed to power a Trinket so yeah makes sense.

    Thanks a lot for your replies @Mark I'll see if I can actually measure the power draw. I'm an electronics n00b but I do have a multimeter and google so we'll see how far I get

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    Hmm well I was not able to measure the current draw.

    I'm still using the same setup but I got rid of the noise by switching to the lineout instead of the headphone jack to connect the audioshield to the AMP. So pretty clean sound now.

    Still I don't understand why I cannot crank open the volume on the amp without the Teensy hanging/rebooting. On USB I can turn it up a more than on battery power, and on 8ohm speakers I can turn it up more than 4ohm speakers, but I don't understand the theory behind this. I mean, I would expect the battery to drain superfast maybe if the AMP is turned way up, but why the error/reboot/shutdown? Those quadcopters fly on lipo, surely they must draw waaaaay more power then my tiny audio project?

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