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.
Fig. 1: Image of Phototransistors
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.
Fig. 2: Image showing 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