Infrared Level Detection Circuit Design

Suitable for measuring liquid levels and detecting proximity events

Up to 50 centimeters range, with an option for relay activation

Circuit Diagram

Components:

Device Purpose:

This circuit is designed for applications involving the monitoring of liquid levels or the detection of nearby objects. It operates by determining the distance to a target object through the reflection of an infrared beam. It safely measures the level of liquids within a tank, without direct contact. The device's operating range can be adjusted from a few centimeters up to approximately 50 centimeters using a trimmer.

The actual range may vary depending on the specific infrared transmitting and receiving LEDs used, and it is primarily influenced by the color of the surface being reflected. Dark surfaces significantly reduce the device's sensitivity.

Circuit Operation:

IC1 generates an oscillator that drives the infrared LED through 0.8 millisecond pulses at a frequency of 120 Hertz and with a peak current of approximately 300 milliamperes. D1 and D2 are positioned facing the target, separated by a distance of a couple of centimeters, on a short breadboard strip. D2 captures the infrared beam emitted by D1 and reflected back from the object it encounters. The signal is amplified by IC2A and the peak is detected by D4 and C4. Diode D3, along with R5 and R6, compensates for the forward voltage drop associated with diode D4. A DC voltage proportional to the distance between the reflecting object and D1 and D2, along with D1 and D2, is fed into the inverting input of the voltage comparator IC2B. This comparator switches the LED and, optionally, the relay, on or off by comparing its input voltage to the reference voltage at its non-inverting input, which is set by the trimmer R7.

Notes: