This light triggered circuit can be used to turn on / off a load such as lamp through the IR rays from a remote or light from a torch. This is an ideal circuit to switch on / off the room light using TV remote while watching the TV .The circuit uses a Phototransistor and JK Flip-Flop IC to give the toggle action.
CD 4027 is the Master slave J-K Flip-flop IC that works in the toggle mode. When the J and K inputs are tied high, at every positive or negative transition of clock pulse at pin 3 can toggle the flip-flop between the high and low states.
Suppose the output of IC1 is low, then T2 will be off and relay remains de-energized to break the load current. When a light, either IR or torch light, hits momentarily on the photo transistor T1, it conducts and a short pulse will passes in to the clock input of IC1 and its output turns high. This high output remains as such till the clock input gets a second pulse. This activates the relay and the load switches on. When a second pulse arrives at pin 3 by triggering T1 again, the output of IC1turns low and relay de-energizes.
Photo transistor pins
The symbol used for T1 is an alternate symbol to show that the gate is not connected. LED indicates the activation of relay.
Circuit Diagrams
Filed Under: Electronic Projects