Modulated photoelectric sensor application circuit

The photoelectric sensor has the ability to resist external light interference, which is crucial to ensuring the normal and reliable operation of the machine. For this purpose, a modulation circuit can be added to suppress
changes in dark current (unilluminated current) in the sensor. When using a modulated reflective light sensor, the ability to resist light interference becomes stronger. Figure 9-s8 shows
a more practical modulation sensor circuit.
    (1) The basic principle of the circuit is that the transmitter part uses a four-NAND gate integrated circuit to form a multivibrator (the oscillation frequency of RP1 can be
fine-tuned), and the pulses are shaped and amplified, and then connected to a 9013 transistor to drive the infrared transmitter. The receiving part consists of infrared receiving tube VD2,
LM393 operational amplifier and LM567. After VD2 receives the infrared control f equal sign and performs photoelectric conversion, it is coupled to the LM393 operational amplifier by C for voltage amplification
. The signal output by the op amp is coupled to LM567 by C3 for audio decoding (frequency selection). RP3 and G determine the resonant frequency of LM567. When
pin ③ of LM567 inputs a signal with the same oscillation frequency as its own, pin ⑧ outputs low level. Otherwise, the output is high level, and
an operational amplifier of LM393 is used to form a Schmitt comparator, setting l. The signal of pin 8 of M567 is connected to the comparator for comparison and then output.