Atmel ATTiny2313-20PU Microcontroller

8-bit AVR architecture (1..2 cycles/instruction; Harvard memory arch)
2kB flash program memory, 10,000x writable
128 bytes RAM memory
128 bytes eeprom memory, 100,000x writable
Serial ports, timers, counters, etc
4 PWM channels (pulse width modulation)
I²C (TWI) slave and master capability
20 pins, of which 18 can be used as I/O
up to 20 million instructions per second at a 20MHz clock
internal oscillator, no external crystal necessary (but can be)
Power supply 2.7 (1.8 for V version) to 5.5V, so also works on two batteries