This circuit is very handy as a timer circuit for a lamp, for lighting a staircase, for example, but can also be used as indicator for the front doorbell. A significant advantage of this circuit is that the circuit draws almost no current when in the inactive state. The circuit is activated with push button (S1), after which IC5 (a 555 timer IC) starts to count down the set time. During this time the triac continues to conduct and the lamp is turned on. The ‘on’ time of the lamp is on is determined by the combination of R1 and C2 and can be changed as required by your application or personal preference. R2 and C3 have been added because the 555 expects a ‘negative’ pulse at its trigger input. When the power supply is turned on, C3 holds the TR input of the 555 Low for a short time, which triggers the timer IC. Circuit diagram : Lighting Governor Circuit Diagram Depending on the exact type (brand) of 555, the value of C4 (330 nF) may have to be changed to ensure a high enou...