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Thread: supply battery teensy 4.0 how do it ?

  1. #1

    supply battery teensy 4.0 how do it ?

    Hi everybody,

    I want supply Teensy 4.0 on battery 5V (4s+adapter).

    How did I do that ?

    Tutorial supply for Teensy 3.2 said use Two 1N5817 Diodes. (with picture I understand)
    But its different on Teensy4.0...And I don't know how do it. (I am not electrician...)
    Do I also use diode or it isn't necessary ?

    Thank's for help.

    Laurent.

  2. #2
    Member pilotplater's Avatar
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    So the biggest thing is you need a stable and accurate 3.3v supply. Byfar the easiest way to do this is use the one that Paul included on the board !

    Click image for larger version. 

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    Attach ground to negative, and the battery-positive to the Vin pin. Ensure the battery you are using doesn't go above 5.5v, and the teensy will start browning out and shutting down below a battery voltage of 3.6v.

    What kind if battery are you using? you said 4S, do you mean like a 4-cell lipo battery? If that's the case that would be way too high voltage to use the onboard regulator (around 15v). In this case instead of or in addition to a reverse-polarity diode you would need a way to step down from ~15v to 5v in order to safely power the onboard regulator. Simplest way to step down like this is a linear regulator. Linear regulators are horribly inefficient though, especially for a battery operated device.

    For a couple more..... bucks..... you can get a buck regulator which will do the job . This one is also a 5v model so would wire into the Vin pin of the teensy.

    One challenge I see is if you used a single cell, max 4.7v LiPo battery, you don't quite get the full capacity out of it before the teensy starts to brown out. For a couple more bucks still you can get a buck-boost regulator which will take whatever you throw at it between 3-12v basically, can't be used with a 4S/15V lipo though, but thought I'd mention it anyway. If you know your battery voltage won't be above 5v perhaps consider a boost regulator like this one
    Last edited by pilotplater; 04-17-2021 at 03:06 AM.

  3. #3
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    I think he refers to this: https://www.pjrc.com/teensy/external_power.html

    A simple "battery" in this case would mean 1.5V (nominal), in 4-series, and adapter would then refer to e.g. buck-converter to drop the 6V (nominal) down to 5.5V or so (to allow a bit for the diode forward voltage). Such setup (with buck-only converter) would perhaps leave some juice in batteries in the end, but it would certainly be an easy setup on the battery side of things. Buck-boost-converter would perhaps work better..

    It seems that Teensy 4.0 (and 4.1) have similar Vin vs. USB-power setup as shown on that guide page, but the pads are in different location. Check the two large pads near the bottom left corner in this image https://www.pjrc.com/teensy/dimensio...y40_photo2.jpg, or the top-right corner in "Teensy 4.0 Back Side" pinout reference card (which clearly mentions the "cut", although not as clear about where to cut exactly: between the pads).

    The diodes are needed only if you want to power the Teensy both with battery and USB; i.e. if either one (or both) is around, things work. If you want to use only the external/battery power, then only the cut is needed. Adding one diode between battery and Teensy is still recommended (the last part of the guide) to protect a bit from accidental reverse polarity connections.

    If adding both diodes:
    A diode would be added between those (cut-separated) pads in the same way like in the guide. The cathode (stripe-end) of the diode connected to the pad closer to the Vin-pin. And similarly, another diode between battery plus-side and Vin-pin, cathode/stripe on the Vin-pin end.

    1N5817... hmm.. certainly does the job, but I got interested if there would be something better. Alas, in the through-hole component selection, not really. And in the surface mount selection, plenty of better choices, but the pads on Teensy are not designed for direct SMD component placement (they are too close to each other).

  4. #4
    Hi Bugy74,

    thank's for your reply. You seem right.
    But could you confirm me this wiring please :
    I use symbolic diode like that : ->|-
    so

    5V_ubec ->|- Vin_T4.0 (5V)
    0V_ubec -|<- 0V_T4.0 (G)

    I am not sure about the 0V diode comparing with : https://www.pjrc.com/teensy/external_power.html
    (this diode seem between 5v and 3V...)

    thank's.
    Laurent.

  5. #5
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    No diode is to be connected to 0V or ground connections (in this case).

    Note that the guide's photo is made with Teensy 2.0, which has a 3 pad arrangement, where the center pad is (nominally) 5V _or_ 3V depending on which side-pad it gets connected with. (And putting a diode in place of the tiny pcb-trace counts still as a connection, so the center is to be at 5V (or more correctly, 5V - diode forward voltage drop). On Teensy 4.0, there is no similar 3V pad.

    I'm not sure which point you refer to with the 5V_ubec (I can't see any such reference/label in Teensy 4.0 photos or schematic).

    Let me try my "artistic" hand on some screenshots for the Teensy 4.0, perhaps they'll be clearer.. well, blue diode drawing with a thin gray strip for cathode isn't that clear on the photo, but should still be easier to understand than a text description. I hope.
    Click image for larger version. 

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  6. #6
    I refer to my own ubec supply wich convert 4S to 5V ,so I call it 5V_ubec (in this case Mateksys UBEC DUO).

    Thanks for the schema I understand where I do put the two diodes (and avoid a mistake ;o)).

    Thank's very much Bugy74.

    Perhaps it's maybe a good idea to put your picture on the site with example T2.2 ( https://www.pjrc.com/teensy/external_power.html)?

    Laurent.

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