This firefly lights flasher is an easy, fun project.
It can be built on the tiny circuit board, or on perf board.
Bill of Materials
(if on perf board, use standard through-hole rather than SMT components)
How the firefly lights works
It functions like almost any 555 astable timer, except that the LED is inserted into the capacitor reset path so that when pin 7 discharges C1 to common, this relatively high current must pass through the LED. In this way, the average battery current is only about 100µA. When battery voltage becomes very low, the LED threshold voltage prevents discharging C1 down to the lower threshold – when this happens, R2 finishes off the discharge because the output switches to ground potential the same time pin 7 turns on – you will find that this works on almost dead batteries that may be useless for other applications. D1 protects against accidental reverse battery voltage.
Fireflies are common through Northeastern US and also in many other parts of the world. This green LED has the same color, flashes at about the same duration and has a similar repetition rate just like a real firefly (lightning bug). Put a number or these around your grounds and they will truly resemble fireflies – there will be no synchronization of the flashes. The only thing this cannot do is to fly – fireflies ascend as they flash, and they do not flash when perched to protect from predators. Also, this is much larger than the tiny firefly beetle that measures about 3 x 20mm.
Visible on the photo is a wire jumper connecting R2 to IC pin 3. This was an afterthought when I found that low voltage operation was poor. The PCB file is updated to fix this. The optional resistor is not used in this case, but is easy to add if desired. You may adjust component values to obtain desired results.
For the Future
Make it extinguish during daylight hours thus doubling battery life to 2 years.