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Fluid level detector
Here is a simple but versatile circuit of fluid level detector which can be used for various applications at home and in industry. Circuit is built around 2-input NAND Schmitt trigger gates N1 and N2. Gate N1 is configured as an oscillator operating at around 1 kHz frequency. When the fluid level reaches the probe’s level, the oscillations are coupled to the diode detector stage comprising diodes D1 and D2, capacitor C4 and resistor R2. The positive voltage developed across capacitor C4 and resistor R2 combination is applied to Schmitt NAND gate N2 which is used here as a buffer/driver. The output of gate N2 is connected to opto-coupler MCT2E. The output across pins 4 and 5 of the opto-coupler can be suitably interfaced to any external circuit for indication purposes or driving any load as desired. Use of opto-coupler ensures complete isolation of the load from the fluid level detector circuit. Since high frequency AC is used for the electrodes, there is no corrosion of the electrodes which is normally observed with DC being applied to the electrodes.

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