TLC555 Low-Power LED Beacon
The CMOS cousin of the 555 runs the same astable circuit on a tenth of the current — perfect for battery-powered blinkers.
Difficulty: Breadboard. Estimated build time: about 30 minutes. Estimated parts cost: about US$2.50. 7-line bill of materials. Compare supplier offers when available. A blinking LED beacon built around the TLC555, the CMOS reincarnation of the bipolar NE555.
Wire the astable around the timing cap
Pin 1 → GND. Pin 8 → VCC (3–5 V). Pin 4 (RESET) → VCC so the chip never resets. From VCC, place a 10 kΩ to pin 7. From pin 7 to pin 6, place a 100 kΩ. Bridge pin 6 to pin 2. Pin 6 → 1 µF film cap → GND. The cap charges through R1+R2 (going HIGH) and discharges through R2 (going LOW), giving the duty cycle of (R1+R2)/(R1+2·R2).
Take the output to an LED
Pin 3 is the output and can sink/source ~10 mA. Put a 220 Ω current-limit in series with a red 5 mm LED from pin 3 to GND, and a second LED + 220 Ω from VCC to pin 3 if you want anti-phase blinking on two LEDs. Don't omit the resistor — even a CMOS 555 will fry a bare LED.
Measure the supply current
Break the VCC line with a multimeter on the µA range. You should see roughly 250 µA quiescent current. Compare with an NE555 in the same circuit (~6 mA) — the TLC555 is dramatically more efficient. With a 220 mAh CR2032, that's months of blinking versus days.