From simple, standard electric cable I built a capacitive sensor to assess the water level in my water container. While the circuit was replicated from this blog (thanks for sharing!), I’d like to share how I built the actual capacitor.
Using ultrasonic distance sensors I monitor water levels for my garden irrigation system. I have an underground rainwater cistern and a wooden barrel as an interim water storage in the sun to have the water warmed up before use. I started off with the classic HC-SR04 ultrasonic distance sensor, but it turned out to be a bad idea for the warm water barrel: Moisture and temperatures up to 40°C in the summer sun made the sensor rot within half a year down to complete failure. I switched to AJ-SR04M watertight sensor (which seems to be very similar to JSN-SR04T which is often also mentioned on the internet). This has a higher minimum distance (~20 cm vs. ~2 cm), and a much larger opening angle (45° to 75° vs. 15°) as compared to the HC-SR04, and in this post I describe how I dealt with that.
I built a treasure chest which opens if a riddle is solved. To prove that the riddle is solved, the players need to put the correct three RFID/NFC tokens (out of several tokens to choose from) onto three RFID readers in the correct order. If they fail too often, a curse is uttered! In this post I describe the hardware selection, the electronics, the assembly and the software.
For a small project I used the ATmega328P MCU – and then the small project somewhat exploded and I needed more and more I/O-Pins. Suddenly all but the PB6 and PB7 pins were in use, and I needed exactly two more…