The schematic is very simple and completely based on the PIC 12F629 microcontroller. This microcontroller has an internal 4MHz oscillator and is packaged in SOIC 8 pin for very compact realizations. The microcontroller is held in low power mode (sleep) until a interrupt from an external pin occurs. The closure of the reed bulb switch force the interrupt and is useful also for circuit switch off when the usage is ended. The two leds are connected via 470 ohm resistor for very low consumption; if the user needs more current for the leds, the resistor value can be consequently decreased.

With the shown components the sleep current is near to 0 (down 1uA) and the mean working current is about 100uA, for about 200 hours of usage.