Category Archives: Projects

This category contains all projects.

Successful Measurements

Using the new method of measurement, described in this post, I could successfully collect some meaningful data. This time, the read values are the exact values of the final sensor without a different kind of oscillator.

I watered the plant at day zero with quite a great amount of water. From there you can see how the frequency slowly rises, while the soil in the flower pot starts to get dry. There is a small measurement error between day two and three. Here I had a short power loss and no data was recorded which resulted in some zero records. Continue reading Successful Measurements

Plant Watering Sensor – Long Term Tests Take #2

I started a second take on the long term tests for the plant watering sensor. This tests are required to be sure, the measurements follow the expected cycles. After watering the sensor, the frequency should go down and while the soil is drying up, the frequency should go up the the initial value.

Logging this measurements is very important to get a good overview of the measurements and be sure if every aspect of the device works as expected. At this point, I especially test the sealing of the foot part of the sensor. If it keeps completely sealed against water, I should get very consistent and repeatable readings.


The curve on the right side shows the measurements of the last 48 hours. These small variations are normal and are most likely caused by the plant itself or because of temperature changes of the board.

If you have questions, miss some information or just have any feedback, feel free to add a comment below.

Plastic Cup Meltdown – Working with Epoxy

Currently I am working on the coating for the foot part of the plant watering sensor. Here I already tried a wide range of techniques and materials. At the moment, epoxy seems the perfect material choice – so I am trying different resins and hardeners to get the best results.

Some hardeners are very reactive and produce a very strong exothermal reaction. While I read and prepared everything meticulously for a new process as usual, I still get sometimes very bad surprises.

For the process, I dip the foot parts into the epoxy resin and hang them up for drying. To waste as few as possible epoxy resin, I used very small plastic cups for dipping.

The exact material of this plastic cups is very important I learned. You should never use something which will react violently with the mixed epoxy resin, as you can see in the next picture.


The cup literally started burning after a few minutes and I had to drop it outside on the forecourt to prevent any disaster. In the picture you can see the remains of the process: A beautiful frozen epoxy block, in the middle of the melt down. The cold air outside rapidly cooled down the process, so the burning stopped.

Mental notes for the next experiments:

  • Use only cups where you exactly know the material.
  • Keep a stop watch running with the pot time, assume 20% shorter time as specified.
  • Prepare an evacuation/meltdown plan. 😉

No Success with First Long Term Measurement

The first long term measurement I made, to test the behaviour of the sensor over a longer time range was a failure. After the five days with the device introduced in this post, the readings made absolute no sense.


The sensor was not moved in the flower pot and the plant was once watered at the begin of the measurement. While it looked promising at the begin, the frequency suddenly went down again, which was very irritating. I am still investigating how this could happen.

To get closer to the real measurement of the final plant watering sensor, I started a new approach.


I soldered a header to one of the LED pads on a fully assembled plant sensor. Next I changed the device for the measurements.


Continue reading No Success with First Long Term Measurement

Plant Watering Sensor – Long Term Logging

To gather more long-term measurements for the capacitive method I use for my plant watering sensor, I created this small logging device. As you can see, it uses one of the plant watering sensor prototypes for the measurements. Instead of using the ATtiny13A on the board, it passes the oscillator signal directly to the microprocessor of the logging device.

In front there is a very small 128×32 OLED display, where I can see the current measured frequency in kHz. On top, the current time and date is visible, and on the right there is a graph where I can see the values from the last 48 hours graphically. There is not much visible in the graph, because I took the photo just after installing the sensor.

Every minute, the current average of measurements is stored in a CSV file on a SD card. After a few weeks I should be able to analyse this file and see the results. Here I am especially interested in the cycles from watering the plant until the soil got dry again. Continue reading Plant Watering Sensor – Long Term Logging

A Versatile ATtiny Programming Adapter

As mentioned in my article about designing a cheap plant watering sensor, I built a small adapter which can be used to pre-program the ATtiny13A. This is necessary, because once soldered on the board, I only have a debugWire interface, which has to be enabled first.


The adapter has a small 50mil JTAG header, where the Atmel ICE can be connected with the board. There is also room for a USB mini jack, which is used to power the MCU while programming. A small on-off switch is used to power the MCU and a LED is placed as indicator to see if the MCU has power. The assembled board looks like this:


One of the DIL/ZIF adapters is mounted on top of the female headers. Most of the adapters for SO-8, SO-14 and SO-16 will work with this board. Continue reading A Versatile ATtiny Programming Adapter

Plant Watering Sensor – Precise Current Measurement

As I wrote in the first part of my article, how to design a cheap plant watering sensor, I had troubles to get exact measurements of the current, using my Testo multimeter. I searched for a solution and found the µCurrent Gold device, from David L. Jones known for the EEVblog. Later a little bit more about the device, first the measurements.


I could do the measurements using the oscilloscope and not only measure the static current consumption, but the current consumption over time. The graph shown in the diagram, is the reading of if the sensor does one single measurement and flashes the LED. Continue reading Plant Watering Sensor – Precise Current Measurement

SMD LEDs Tests

Today I tested a number of SMD LEDs for the plant watering sensor project. I soldered all 13 LEDs I shortlisted onto a small board and connected it to an Arduino Zero Pro. So I could try the different flashing styles I planed to use more or less automatically. That way I could focus on the LED flashing itself, without being distracted by switching cables.


This is the board I made. Very simple but functional. I used red and blue male header to mark the anode and cathode of the LEDs. There is a sticker on the bottom with the LED numbers on it.


I mounted everything on a very small breadboard and did all connections to the Arduino.

Continue reading SMD LEDs Tests

The Fan Controller Wrapped Up

Yesterday I found some time to put the fan controller in a casing. I used a very cheap no-name case with the dimensions 130 × 68 × 44 mm. First I drilled some 2.5mm holes into the lid, and fastened the Arduino board on it using M2.5 spacers. You see the bottom of the case in the photo – I mounted everything top down, because this simplified everything.

I experimented with the spacer size, until I found the right height, so the display is more or less at the same height as the case bottom. Next I put very small bits of double sided tape onto the corners of the display and put the case bottom on top of the lid. After removing the bottom, the exact position of the display was marked at the bottom with these double sided tape bits.

First I drilled four holes at the expected corners to see the position from the other side. Next I used a Dremel tool to cut the rectangle out of the case.

As usual: This was my expectation of the result… 😉


…, and this was the actual result:


No, seriously, I did not expect much. I just hoped the controller will fit into the case and I cut the rectangle at the right place. So, this worked out very well.