Automatic Light Switch Circuit Schematic
Here is an ultra simple automatic light switch circuit for bedrooms. After construction,connect the input terminals of this circuit in parallel to the internal buzzer terminals of a Quartz-Alarm Clock. When the clock alarm is activated at a time set by the user, electromagnetic relay in the circuit is energised for a short duration, controlled by the timer IC 555.
Contacts of the relay can be used to switch on a bedlamp, table lamp or similar electric light loads. The circuit works off unregulated 12V.U se any12VDC/500mA rated standard ac mains adaptor.
When the clock alarm rings, input pulses are fed to the trigger input point (T1+Pin2) of IC1, through an RC filter (C1,R1&C2). Here IC1 is wired as a monostable and dc voltage at its output (Pin 3) terminal goes high instantly after receiving a trigger,and remains in the condition for about10 seconds, as configured by the components values of R3 and C3.
Output from IC1 directly drives the low current relay RL1 through diode D1. Note that diode D2 is here used as a freewheeling diode to suppress the counter emf generated during relay switching.
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