One of the very low cost ($4) liquid level sensor with excellent performance. Unlike many liquid level sensors other than ultrasonic require probes to be inserted to the liquid. This causes electrolysis and after few days it stops working properly. Non touch-types Ultrasonic has the disadvantage of getting damaged if accidentally comes in touch with liquid or outdoor use. Presented below an optical sensor-based system that works on the principle of IR light reflection and refraction through a prism.
As seen on the diagram below the inbuilt IR light falls on the inbuilt phototransistor if no liquid is seen in front based on internal reflection. Thus the phototransistor conducts and its emitter goes high which can be used to drive any logic circuit. But once it comes in contact with the liquid, by the refraction of the IR light in the liquid medium gets diverted from the phototransistor driving it to off condition thus the output goes low.
The $4 optical liquid level sensor applications–
Example of Swim pool application to avoid dry run resulting in burning of motor.
House the $4 sensor in a small enclosure, Get a $1 clamp from Dollar tree, Get a $10 solar light ( use the housing and built in the LiPo 18500 mH battery for powering the circuit) from Home Depot or Lowes, Get an ESP8266 online at $2 or a Nodemcu ESP at $3, Create an account in IFTTT if you don’t have, make your own applet in IFTTT, open an account with webhook, get a key, take a phone service (only in USA) if not then a yahoo mail in IFTTT and feed your telephone number, get the program from github, load on to the ESP and the job is done at in less than $20 :– Watch video
Upon touching the water the output goes low.
Pumps, bathtubs, sanitary ware, medical equipment
Steam and other level control equipment