Simple flasher operates off ac mains

摘要

H Looking for a mains switch in the dark is easier if the switch contains a built-in neon or filament miniature lamp. Adding a small indicator to any mains switch is helpful. It is even better if the indicator flashes. This circuit makes a simple flasher using only four discrete components (Figure 1). The neon lamp flashes at a frequency of 1 to 5 Hz, according to experimental values for resistance and capacitance. When the switch termi- nals are open, diode D_1 acts as a half-wave rectifier. Capacitor C_1 charges through resistor R_1 until the voltage on the capacitor exceeds the breakdown voltage of a miniature neon lamp. C_1 then discharges rapidly through the lamp, which flashes.