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Thread: Teensy 2.0 - power consumption

  1. #1
    Junior Member
    Join Date
    Mar 2015
    Posts
    2

    Teensy 2.0 - power consumption

    Hi,

    I'm experimenting with Teensy on low power, and found something that I can't explain.

    Currently Teensy runs on 3.3V and 4MHz.
    When I power it up, consumed current is 12.4mA.
    It's very different from my expectations, because it should consume 10.6mA on 3.3V/8MHz, so on 4MHz it definitely should be less than 10.6mA.

    When I connecting USB, and consumed current drops down to 7.5mA.
    Wow.
    I expected that USB will eat some additional power from battery.

    And when I'm disconnecting USB, consumed current drops down again to 4.2mA.
    Hmmmm....

    And now when I'm connecting/disconnecting USB, consumed current is 7.5/4.2mA.


    I tried to power it up with connected USB, and then I see 7.5/4.2mA from the beginning and there is no 12.4mA peak.


    I'm using TMK firmware for my experiments (https://github.com/tmk/tmk_keyboard/...eyboard/onekey) because I'm familiar with it, and after all I want to make BT keyboard
    Everything I've changed - it's just set cpu prescaler during matrix initialization:

    Code:
    --- ../onekey/matrix.c  2015-01-03 13:38:59.383088670 +0200
    +++ ./matrix.c  2015-03-06 04:07:57.022047139 +0200
    @@ -21,6 +21,7 @@
     #include <stdint.h>
     #include <stdbool.h>
     #include <avr/io.h>
    +#include <avr/interrupt.h>
     #include <util/delay.h>
     #include "print.h"
     #include "debug.h"
    @@ -57,6 +58,12 @@
     
     void matrix_init(void)
     {
    +    // set CPU speed
    +    cli();
    +    CPU_PRESCALE(CPU_4MHz);
    +    sei();
    +
         debug_enable = true;
         debug_matrix = true;
         debug_mouse = true;
    Obviously, TMK firmware does not doing something on start, what it doing when USB is connected.
    This "something" is very influencing to power consumption.
    Unfortunatly, I have no clue what this could be.

    Any help, ideas and directions to experimenting really much appreciated.
    I need full power of your telepathy

    (also cross-posted on GH: https://geekhack.org/index.php?topic=69606)

  2. #2
    My 2 cents: when connected to USB the power comes from your computer via the 5v,gnd pins on the usb. so you wont be able to see it from the current meter which monitors the battery.

  3. #3
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    22,109
    Maybe you could post a photo showing exactly how you have the power and power actually connected, and which traces cut and pads soldered on the bottom side.

  4. #4
    Junior Member
    Join Date
    Mar 2015
    Posts
    2
    I've got answer on GH: https://geekhack.org/index.php?topic...626#msg1669626
    This is just specific of TMK, it busy-waiting for USB connection, so all is fine with Teensy itself.
    Thanks to all!

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