Here we present two open-source, do-it-yourself, microcontroller-powered holiday electronics projects, A micro-readerboard Christmas tree ornament and a mini-LED Hanukkah menorah.
These two projects are based on the Atmel ATtiny2313, a powerful little 8-bit AVR microcontroller. This microcontroller is an inexpensive single-chip computer complete with a clock, 2 kB of flash memory, and 128 bytes each of SRAM and EEPROM memory.
As we have the chip configured, 17 of the chip’s 20 pins can be used as logical outputs to directly drive LEDs. The remaining three pins are for power (2.7 – 5.5 V DC), ground, and a reset pin reserved for programming use. You can find a diagram of that configuration here.
Since the microcontroller is a little computer, it doesn’t really do anything without a program. We wrote our two programs in C, and they do basically what you’d expect: tell the chip when to turn the different lights on and off. There’s a little bit of work in building the font table for the ornament, but even that isn’t so bad.
One trick that we used: An integer representing the current message displayed on the ornament (or the day on the menorah) is stored in EEPROM, a type of nonvolatile memory, in order to let the chip change its behavior from the previous time that it was turned on. Once the code was written, we used open source, cross-platform development tools (including avr-gcc and avrdude) to compile the C code into a binary firmware object and program the device through a low-cost USB programmer.
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