Infrared receiving circuit diagram with pre-integrated amplifier

As shown in the figure, due to the use of integrated amplifiers in the circuit , the circuit is simple and the volume is small. The TDA4050 integrated circuit is used here. The weak infrared signal is received by the photodiode VD and is first amplified by the transistor. Due to the use of a condenser lens (diameter of about 15mm, focal length of about 30mm), the effective distance can be increased by 20 to 30 times. Capacitor C can effectively reduce low-frequency interference signals in the range of 50 to 100Hz.