This light-driven circuit can be used to turn on/off a load, such as a light bulb, via infrared rays from a remote control or light from a torch. This is an ideal circuit to turn on/off the room light using the TV remote control while watching TV. The circuit uses a phototransistor and JK Flip-Flop IC to give the switching action.
CD 4027 is the JK Master Slave Flip-flop IC which works in toggle mode . When inputs J and K are turned high, with each positive or negative transition of the clock pulse on pin 3, the flip-flop can switch between high and low states.
Fig. 1: Image of Phototransistors
Suppose the output of IC1 is low, then T2 will be turned off and the relay will remain de-energized to stop the load current. When a light, whether IR or torch, momentarily hits the phototransistor T1, it conducts and a short pulse passes to the clock input of IC1 and its output goes high. This high output remains as such until the clock input receives a second pulse. This activates the relay and the load is switched on. When a second pulse reaches pin 3 triggering T1 again, the output of IC1 goes low and the relay is de-energized.
Fig. 2: Image showing the phototransistor pins
The symbol used for T1 is an alternative symbol to show that the gate is not connected. LED indicates relay activation.
Circuit diagrams
| Toogle_0 optical circuit |  |
