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Power bank keep alive device

https://bues.ch/cgit/pbwake.git/

Pbwake is a small USB stick to prevent power banks from shutting off the outputs and falling into deep sleep mode.

Pbwake uses tiny load pulses to simulate a real load on the power bank outputs. The lengths of the load pulse active (high) and inactive (low) phases are pseudo random within configurable bounds.

Pbwake is in a low power state during the inactive (low) phases. Therefore it doesn't waste too much power and guarantees high battery life of the power bank.

Tested power banks

Power banks this has been tested with are:

  • Anker PowerCore 20100 model A1271.
  • No-name power bank 2200 mAh / 11 Wh with integrated flashlight LED.

Microcontroller

Pbwake supports the following microcontrollers:

  • ATTiny-13
  • ATTiny-25
  • ATTiny-45
  • ATTiny-85
  • ATMega-328P

Hardware schematics

Schematics: schematics/pbwake-attiny/pbwake.pdf

The hardware may be built manually on a simple prototype board.

Board front side:

doc/pbwake_front.jpg

Board back side:

doc/pbwake_back.jpg

Prebuilt firmware images

The release archives of pbwake contain prebuilt .hex files for all supported microcontrollers in the hex directory. These hex files can be flashed directly to the microcontroller with a any tool of your choice (e.g. Atmel Studio or avrdude).

The corresponding fuse settings can be found in the file fuses.txt in the same directory.

Building the firmware

The firmware build needs the following tool chain:

  • Unix-like operating system
  • GNU make
  • AVR GCC
  • AVR Binutils
  • avrdude

Run the following commands to build the firmware:

cd firmware
make DEV=t85

Please specify the target microcontroller using the DEV variable as shown above.

Valid values are:

Microcontroller make option
ATTiny 13 DEV=t13
ATTiny 25 DEV=t25
ATTiny 45 DEV=t45
ATTiny 85 DEV=t85
ATMega 328P DEV=m328p

Additional build options that can be passed to make:

make option default description
CONF_HIGH_MIN_MS 4 Minimum length of high-phase (in milliseconds).
CONF_HIGH_MAX_MS 6 Maximum length of high-phase (in milliseconds).
CONF_LOW_MIN_MS 40000 Minimum length of low-phase (in milliseconds).
CONF_LOW_MAX_MS 55000 Maximum length of low-phase (in milliseconds).

Flashing the firmware after build

Run the following commands to flash the firmware to the target microcontroller:

cd firmware
make DEV=t85 print_fuses
make DEV=t85 write_fuses
make DEV=t85 write_mem

Or alternatively use any other of the available AVR flashing tools to program the .hex file and fuses.

License

Copyright (c) 2020 Michael Buesch <m@bues.ch>

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.