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HELEN

HELEN Pendant

600px|center The HELEN board is my version of the Adafruit GEMMA, an Arduino-like system built on the AVR ATtiny85. The major change relative to the original is that the HELEN has disabled the !RESET pin so that it can be used as a fourth IO and has twelve 0805 LEDs arranged in a circle. These are driven with charlieplexing and have full PWM control. The other change is that the HELEN uses a MicroUSB and has a built-in holder for the LIR2450 lithium coin-cell on the back. It might turn into a Burning Man pendant gift.

V1

The boards were ordered on 2015-01-20 and have some problems:

  • PINB3 is not the same as pin 3. Oops. The USB wire needs D+ and D- swapped. Due to another mistake, the pullup is now on the right pin.
  • ATtiny85V-10SU will not work -- only the ATtiny85-20SU can go fast enough to do the USB at 16.5 MHz.
  • Disabling the reset pin has proved harder than I had anticipated. I've bricked many of the SOIC chips and had to rework them.
  • Reusing one of the USB pins will require a change to the bootloader to drive any of the other pins due to charlieplexing.
  • The through-hole version of the battery would allow the board to be slightly smaller.
  • Adafruit GemmaBoot doesn't seem to compile or work anymore.

  • Reworked GemmaBoot to disable LED flashing, which allows D- to be reused as an IO pin. github.com/osresearch/gemma-bootloader has the changes; they were mostly in the build process.

  • Swapping the D+ and D- pin on a USB cable worked and allowed me to flash the device.

  • All 12 LEDs work now.

  • Time to update the schematic and make the board in the different designs.
  • Encased one board into a coaster.

BOM

2015 AVR LED OSHPark

Last update: November 8, 2020