InfraRed (IR) Sensor/Detector Circuit
The IR circuit described below is mainly designed for liquid level detection or proximity detection. The IR sensors used here are an IR LED and an IR photo diode. The circuit operates by detecting the distance from the target by reflection of an infrared beam. The biggest advantage of this circuit is that there is no physical contact with the liquid whose level is to be measured. Such a circuit needs to be installed only once, and can be used for years, as there is no corrosive elements.
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The circuit shows that the output of IC1 555 IC, which is designed for a duty cycle of 0.8mSec, with a frequency of 120Hz and 300mA peak current, is used to drive the infrared LED, D1. From the connection it is clear that the diodes D1 and D2 are on the same line, just a few centimeters apart, on the breadboard. Thus diode D2 receives the infra-red output from the diode D1. The diode signal, which is given to the inverting terminal of the op-amp IC LM 358 gets amplified and its peak is detected by diode D4 and capacitor C4. The forward voltage produced by diode D4 is compensated by diode D3 with R5 and R6. According to the distance between the infrared transmitter and receiver, a proportional DC voltage is fed to the inverting input of IC2. According to the output of the comparator the LED is turned ON and OFF and this is detected by the transistor Q1. Thus the relay is driven according to the output of Q1. The comparator output is set according to the value of the pot.
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The range is set by adjusting the pot. Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device’s sensitivity.
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Use a good quality regulated power supply. The sensor diodes must not be subjected directly to other light sources.
|Resistance R2, R5, R6, R9
|Resistance R4, R8
|Trimmer Cermet R7
|Capacitance C3, C5, C6
|Diode D3, D4
|Diode D6 ,D7
|PNP Transistor Q1
|Timer IC IC1
|Two ways output socket