Hauke’s Projects

Playin' around with Electronics and Computers

Microcontroller

Posts that involve the usage of a microcontroller, like AVR or PIC.

Soil Water Sensors: Problems with the Ubiquitous DFRobot Capacitative Sensors

Capacitative soil moisture sensors based on this DFRobot-design (and its successors) can be found in numerous blog articles about irrigation automation. For me, they do not work out for two reasons: a) A notable temperature dependency of the measurements, and b) a high failure rate after a few months to a few years. I decided to adopt the concept of my Simple Capacitive Water Sensor for a Water Container for soil moisture measurement, which turns out to work well.

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Simple Capacitive Water Sensor for a Water Container

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.

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Lessons Learned: Measure Water Levels in a Barrel with SR04-Type Sensors

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.

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Quick Thing: Case for Diamex All-AVR Programmer

The Diamex/Tremex All-AVR programmer for ATmel microcontrollers comes as “naked” populated PCB, no case, no protection against shorts or other damage. I created a case for it, with the following design criteria:

  • Protection against accidental shorts as good as possible.
  • Easy access to the jumpers that control the various operation modes.
  • “Park position” for the jumper that de/activates the external power (since it is often in “off” position and can easily be lost).
  • LED signals need to be visible.
  • Uses the existing mounting holes.

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RFID Treasure Chest for LARP

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.

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Title Image Project: LED Controller

To create a lamp with adjustable color temperature and brightness, I use a warm/cold white dual LED strip, an ATtiny45 MCU with N-channel MOSFETs and two adjustable resistors. This article contains the hardware and software setup. The title image of this blog shows the project.

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