Proximity sensor that is not affected by the environment

Proximity sensors that use infrared light are easily disturbed by sunlight or light and malfunction. The proximity sensor introduced in this article emits infrared light modulated by pulses in its light-emitting circuit, and the receiving circuit uses a filter to detect only the required frequency components, thereby avoiding the influence of ambient light.

Figure 1 is a light emitting circuit. The infrared light emitting diode model is TLN15A, and the peak wavelength is 950nm; the Schmidt NAND gate circuit 74HC132 generates a modulation pulse, which is amplified by the transistor 2SA1296 to drive the infrared light emitting diode, with a duty cycle of 25% and a peak current of 150mA.

Figure 2 is the optical receiving circuit. The infrared photosensitive diode model is TPS703, with a peak wavelength of 950nm; the high-pass filter is used to filter out the 50/60Hz frequency interference of the mains; the low-pass filter is used to filter out the 38kHz frequency interference of the infrared remote control: the amplifier NJU7032 outputs a pulse-modulated AC signal, which is rectified by a Schottky fast recovery diode and then amplified by the amplifier for DC output. The detection signal of the TTL level.

The working distance of this proximity sensor can reach 1m. To increase the working distance, the duty cycle can be adjusted to 10%, the current of the infrared light-emitting diode can reach 300mA, and a focusing lens can be installed in front of the light-emitting and light-receiving elements.