I want to build a water sensor that disconnects the motor when:
1. tank is full
2. water in input pipe is missing.
I came up with the following schematics (haven't practiced much electronics in last 10 years :))
The sensors are just 2 wires (R1, R2).
- R1 (priming water sensor) is the resistance of input water (let's say 2K when water present and 1M when water missing). This makes sure the motor is not running without water.
- R2 (tank full sensor) is the resistance of second water sensor.
Seems to work but I see a residual current (few mA) in the relay. The relay makes contact at 15mA, but I think firm contact is at 25mA.
I need to know if the relay might oscillate. Do I need some kind of digital trigger to make sure the relay is either on or off, but not in the middle?