Using NE555 to make a universal remote control switch

The advantage of this remote control switch circuit is that it has audible and visual effects to indicate the receipt of the remote control signal sent by the remote control module and is used to switch the household appliance on or off.

The circuit consists of power supply, transmitting part and receiving part. The power supply is provided by stepping down the mains voltage, rectifying and stabilizing it with 7805 to provide 5V DC voltage.

The transmitter part (Figure 1) is a monostable circuit built around the NE555 timer (IC4). It uses two infrared LEDs to emit infrared light. VR1 sets the output frequency of IC4 to 38kHz. The transmitter part is powered by a 9V battery.

The receiving part (Figure 2) consists of infrared detector TSOP1738 (IRX1), timer NE555 (IC2), counter CD4022 (IC3) and some discrete components.

When the switch S2 of the transmitting part is pressed, the TSOP1738 of the receiving part detects the 38kHz infrared signal and then outputs a clock pulse. This pulse is amplified by the transistor T1 and added to the trigger pin ② of IC2. IC2 is designed as a monostable multivibrator. Once IC2 is triggered, its output pin ③ maintains a high potential for a specified period (T), which is given by the following relationship: T=1.1xR6xC7 seconds. This delay can prevent the circuit from being triggered by mistake. The output of IC2 is used as the clock input of IC3, and the output pin ① of IC3 is connected to the base of T2 through the resistor R10, and then drives the relay RL1 through T2. After RL1 is attracted, the load is connected through its contact N/O.

When the next pulse reaches the clock input of IC3 through IC2, the state of IC3's output pin ① is reversed to a low potential, T2 stops conducting, and the load power supply is cut off. LED2 of the receiving part indicates that the signal is received; LED3 indicates that the load is in the off state; LED4 indicates that the load is in the on state.

During installation, the transmitting part uses one PCB board, and the power supply and receiving part share one PCB board. After installation, put the two PCB boards together into a plastic box, and make the TSOP1738 face forward. It is convenient to receive the transmitting signal.