Fluid Level Detector #1:

Fluid Level Detector #2: Circuit is built around2-input NAND Schmitt trigger gates N1 and N2. Gate N1 is configured as an oscillator operating at around1 kHz frequency.

Sonar like method detects fluid level: 07/19/2001 EDN - Design Ideas / Figure 1 illustrates a simple, cost-effective method of measuring the height of fluid in a column by using ultrasonic waves. tw1o piezoelectric transducers generate and listen to the ultrasonic acoustical wave.