You can check how full the 30-liter fresh water tank is by pressing a button at the entrance. We also wanted an audible indicator when it's time to refill the tank, without having to press a button. And if you fill the tank from outside the caravan, water always comes gushing out because you have no idea how full it is already.
So, we're making an audible "almost empty" indicator and a "full" indicator. As a water sensor, we're using two XKC-Y25-NPN sensors. This is a very reliable contactless sensor that can be simply glued to the outside of the water tank.
1) Tank full indicator
When the water tank is full, a short beep will sound. A LED will also illuminate the filler opening on the outside of the caravan. For the power supply, we use the 12V DC available next to the water tank, which we reduce to approximately 5 volts using a voltage regulator or buck converter. (Do not connect the black wire from the sensor to ground.)
2) Tank nearly empty indicator
Based on a simple CMOS IC, the 4093, we will hear a few short beeps below a certain water level. IC1a detects when the sensor's output goes high. (With some delay so splashing doesn't matter.) The duration of the acoustic signal is determined by R2 and C2 (with these values, about three seconds). IC1d ensures that the buzzer switches on and off quickly several times. Again, the black wire from the sensor is not connected. We build both circuits compactly on a piece of experimental PCboard.
On the left is the sensor with the "full" indicator. The white area is glued to the water tank.
On the right is the "almost empty" indicator with the sensor connector. The connector is marked for proper connection.
Below are the small experimental PCboards on which the circuits are built. Of course, they can be combined with a single voltage regulator and a single buzzer. But these days, those are two-cent components.
Additional photos will follow once we have installed.
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