Since I put the 18650 battery in the reverse side of the charger unit twice, I started thinking about how to prevent this. I found a tutorial on the web, where a development is presented, with step by step improvements. The address is:
From this I have only picked out the last protection circuit:
I made myself an isometric picture of this, because I have no idea about the placement of the MOSFET transistor pins.
Here is a photo of the circuit, you can see what kind of leads I have used and how I have soldered the components to the board.
Another photo of the same circuit. I did indeed connect the 18650 correctly first. No fume rose from that. I was quite relieved. I had to gather all my courage before I put the 18650 battery in the wrong way round. Now I have a new multimeter, which also has a current measurement feature. The right way up the charging current was about 14.3 mA, the wrong way up there was no current at all. So it works now. I soldered another copy of this wiring tonight, so if I have two compass belts, I could protect both from inserting the battery the wrong way into the case!
In connection with the flower watering arduino experiments, I wanted the same amount of water to always go to the four flower pots. I imagined it would be easy to do, but it's not. For some reason, the water always goes to one flower pot too much, and the other flower pot has nothing. I imagined that if I made holes of the same size, it would work. First, I made a trial version out of plastic blocks by gluing, and by poking with a needle I made holes of the same size as possible, a bit similar idea to hospital infusion drip devices. It didn't work, always a hole was a little bigger and then the water only went to one pot. That's why I decided that if I tried 3D printing, the holes should be precise. It still didn't work. What it looked like on the inside looked like half.
That's what the stl model looked like from the outside. I saved the "stl" file of that 3d model to the Cloud server, because the file was too big, I could not sent it as an email attachment. When I drew the model with the Unigraphics program, nowadays the name of the program is "Siemens NX", it was also a nice exercise in 3d modeling for me. For example, I had to remember that a 3d printer cannot have arbitrary protrusions, because it always prints a layer of plastic on top of another layer, and when that plastic is a bit hot, it might clump up a bit and lose its shape. Siemens NX is very suitable for modeling special wavy and curved surfaces.
I found the printing service on the www.tori.fi website. www.tori.fi is mainly an online sale of used goods, similar to what the yellow pages used to be. The 3-d model cost me about 15 Euro, and it came by mail quite quickly. Anyway, that 3d printing experiment wasn't worth the effort because my principle doesn't really work. The water dispenser must have a different shape. A functioning shape is on the website:
As an impulse buy, I bought a very cheap LIDAR. Partly also becuase I already saw from a youtube blogger that it is possible connect some lidars to the arduino. And even though the construction of the robot still seems like a too large project for me, well, I can still have dreams. ... to use servo motors, an arduino and other sensors to make such a nimble looking toy that can drive around my flat, and of course the Lidar would be the eye of the robot, so that it would not crash into doors and hurt himself, but my robot would always stop safely before any obstacle. This is still a complete dream. The hindrance is a lack of time and maybe also patience. I would probably need quite many weeks in a row to focus only on this, but I can't spend all weekends on this, after all, I have many other hobbies and other mandatory household chores. Anyway, this little project could be one little step forward on the long road to making my own robot. This is the link to where I bought this wonder device.
When I bought this LIDAR, I still imagined that I would connect it directly to an Arduino, at least that's what the Swiss blogger did, where he had a completely different converter, which I also bought, but which is now still awaiting its destiny while lying around among in the heap of my other electronic stuff. But actually this connection directly to the USB port of the computer is at least for me already easy, because the programming tool Visual Studio Code, and python is pre-installed and reasonably familiar to me. The required plug-in module for the computer's USB port can be found at the following link. According to wikipedia TTL stands for Transistor-Transistor Logic, the name means that transistors, bascially 2 circuits in series both amplifiy and performs logical functions. I don't think it means anything, but it's a converter between the USB port and the RS232 serial signal. I still remember that the abbreviation RS232 appeared with the C64 computer. Link:
There is also a reference on Lidar's sales site to find the right program snippets for decoding the signal. This Discord discussion group came into the public eye because an American posted secret photos and other information about the war in Ukraine, apparently just bragging how much he knew. On that specific channel named mb_1e2tydlidar-s4b there is a man called VIDICON who has been investigating this lidar deeply. Apparently the seller has not provided any documentation about this device. Not to say that it is not untypical of Chinese vendors. VIDICON apparently has the appropriate signal analysers to gradually work out what all the its and bytes of data packet means that the device is putting out. Wow, I have great respect that such gurus like VIDICON are around in this world. By the way, even though the code comes from github, that for me it was not exactly a one-to-one, but I had to experiment a bit, what kind of baud-rate it works with, turned out to be 153600. Fortunately my computer already had python installed with VS Code, but I had to add the additional modules pygame, serial, math and enum. I can't remember, something similar like sudo apt-get install -y enum was necessary or maybe the equivalent on a windows machine.
The program as listed here is not exactly the same as the github program, but in addition to baudrate, I changed the pygame command set_at, which produces only a very faint dot on the screen, and replaced it with a rectangle pygame.draw.rect, which is much better visible. I also tried pygame.draw.circle, but it's just too slow, makes a lot of horizontal lines on the screen. I also changed the magnification factor, distancef = distance / 40 then when I want more details to be highlighted, my own face profile as an example, then I set this factor to 3. However, I am quite unfamiliar with pygame and the whole program is like Hebrew to me, especially this class State(Enum). I'll still have to get familiar with it.
LIDAR connection scheme to computers USB port
Testing the LIDAR by walking around in my flat
This seems to be a pretty common type of Arduino project. I’m terribly lazy to water my flowers, often forgot for weeks, and I want the flower to be watered automatically with a pump whenever the water runs out. The setup includes an Arduino Uno, water pump, water hose, water level sensor and Arduino adapter card, and a blue relay.
Arduino program code