ULN2429 liquid detector circuit diagram

This electronic liquid detector circuit diagram is based on the ULN2429 monolithic bipolar integrated circuit designed for detecting the absence or presence of many different types of liquids . The ULN2429 electronic liquid detector circuit can be used in automotive , home or industrial applications .
The absence or presence of the liquid is determined by comparing the loaded probe resistance (probe immersed in the fluid ) with an internal or external resistance . At the output you can connect a LED , incandescence lamp , loud speaker or even such relays or solenoids, but just I you connect at pin 12 a capacitor , to provide a dc output ( typically the output signal is a square wave ) .
If you need to connect at the output a device that need more than 30 volts you can use the ULN2429A-1 which is identical , but support devices with operation up to 50 volts .
This detector electronic circuit need to be powered using a power supply that provide an output voltage between 10 and 16 volts .