“Everyone loves blue LEDs and everyone loves coin cell batteries, but if you want to power a blue LED from a coin cell you will need some help. Here is a super-cheap and easy way add a to boost your LED voltage with only an additional capacitor & diode, and a little software. I love that Atmel AVR chips (ATTINY, ATMEGA, Arduino) can run directly on battery voltages from 1.8 volts up to 5.5 volts. I also love that they can drive LEDs directly connected to their IO pins. If you connect a ATTINY directly to a CR2032 and a red LED and blink your life away until the battery is almost completely dead. Most blue LEDs need more than 3 volts to light up. A brand new CR2032 coin cell makes about 3.2 volts on a good day, and it is all down hill from there. So how can we light a blue LED from a coin cell?”