Power failure and resumption alarm cum indicator circuit using 555 timer ic
Bty, Diode D1,D2, Led L2 and resistor R2 are wired in such a way that the led L2 lights up only when power fails. When the power fails, the transistor Q1 is activated and is powered by the charge stored in the capacitor C3. Increasing the value of C3 from 1000uf to 2200 or 4500uF, increases the duration of the alarm during power failure.
- Q1 - BC558 (PNP)