Big 7-segment countdown timer
Paul over at Dorkbotpdx has written an article about his 7-segment countdown timer:
This entry was posted in DIY, LEDs and tagged 7-segment, timer.
The main challenge was driving the LEDs with a constant current, because they need about 10.5 volts across the several series LEDs. I wanted to run from 12 volts, so there wasn’t much voltage left over for the normal current limiting resistors. Instead, I used this opamp circuit.