Today prototype boards from Eurocircuits arrived. The quality of this boards is outstanding. I do not know any other board house which delivers this incredible quality of boards. They really thrive for perfection.
Recently I finished a small cat feeding device. Meanwhile I added some minor missing parts, like an USB port which can be used to charge the device. I also added a larger battery to keep the device running for months without charging.
Here a short video demonstration of the project:
I finished a very simple and quick project recently. It is a programmable cat feeder device. The device is just made for one single portion, but it uses this slide which produces the distinctive sound if the pellets hit the bowl. It is no replacement for the usual feeding of the cat, but some flexible addition to give food out of the regular times.
The whole build was done in roughly four days, using a very quick prototyping and build method.
First I had to make a decision about the final size of the device. I used Autodesk Fusion360 to create a model of the device and try to fit all required parts into the device.
This is one of the last designs I made until I had the right size. I used a different mechanism as shown here, the important part was to get the right size.
Next I bought plywood in the right sizes for the outer shell of the case. I also got some additional panels fitting inside of the shell for the internal structure.
I created the shell with four sides, left the top and front side open. To work quickly I fastened the panels with hot glue in place. This has the benefit that you can remove panels using a hot air gun in the prototyping stage.
There was a long delay with no update about my projects. The reason for this is, I focused on other non electronic related projects. I promised to publish all files and information about the plant watering sensor project in August, and here are all the files.
Even with these files, it is a very advanced project to do. To produce the PCB, you need a board house which is used to precise and high quality PCBs, like Eurocircuits. Also all pads are prepared to reflow soldering, and not hand soldering. It may be possible to solder the resistors in place using a regular solder iron, but it will be hard to do.
This is the sixth part of the meta-tutorial, where I talk about designing a cheap plant watering sensor. If you did not already read the first, second, third, fourth and fifth part please do it now. These parts contain a lot information which lead to this point of the tutorial.
The fifth part ended with step 24, where I talked about calculating the total bill of materials. This part will focus on preproduction of a small batch of sensors to solve some final details.
Just note, I obviously do not follow these steps in a perfect sequential way. Often I start with some tasks earlier and things are running in parallel. There are various dependencies and it would make no sense to wait with some task just to follow a strict sequence. 🙂
If you follow my blog you may already read some details about ongoing tasks. I will just briefly talk about them in this article. You will find more details in the other blog posts.
Everything looks very promising, so its time to build a small batch of the final devices to see if they work as expected. This is also a test to see how a larger number of these devices can be produced and what kind of tools are needed for this task.
First I order the components. This is very important, because the availability of electronic components changes all the time. It is nice to have all required components, so you can order the boards with the correct footprints. If you order the boards first and are unlucky, an important component is suddenly unavailable and you have lots of boards with wrong component footprints on it.
The components for the plant sensor are really cheap, so there is no huge risk. Even it turns out a huge issue requires a component change – it will be a small loss. SMD components also do not take a lot of space, I can easily store all of them in a very small box. Continue Reading
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
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.
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:
I received the foot parts of the plant watering sensor from Eurocircuits. As you can see, they have the same great quality as the head parts.
Eurocircuits removes any bridges from the boards in a very clean way, so you get the boards with exactly the shape you designed. This saves a lot of work and add to the beauty of the boards.
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.