I knew almost nothing about electronics before following the Fab Academy.I had to learn and understand the very basics of a electronic circuit and its composents, but also of electricity and its flow.
To do so, I designed a pomodoro timer from scratch. I have learn a lot throughout the process and I have the feeling that this new knowledge will play a key role in what I will do for my personal project and afterwards.
I use a pomodoro timer daily to help me manage my time and effort in the tasks I want to accomplish. For now, I'm using Pydoro, an open source pomodoro terminal timer written in Python but I would like to build mine and have it physically next to my laptop.
The Pomodoro Technique is a time management method developed by Francesco Cirillo in the late 1980s. The technique uses a timer to break down work into intervals, traditionally 25 minutes in length, separated by short breaks. Each interval is known as a pomodoro, from the Italian word for 'tomato', after the tomato-shaped kitchen timer that Cirillo used as a university student.
The main component I'm using is the microcontroller ATtiny1614. It will allow me to program my inputs and outputs needed to run my project.
As outputs, I have 4 LEDs that are used to visualize the time passing by and the interactions with the pomodoro timer.
As inputs, I have to 2 switches (buttons) that allow me to start/pause/resume/reset the timer.
I also need 6 resistor (one for each of the inputs/outputs), a capacitor, a FTDI header (to be able to communicate with the boards), a UPDI header (to program the board).
I'm using KiCAD, a cross platform and open-source software, for designing electronics. The process is divided into two main steps: schematics design and PCB design.
Before making the schematics, I had to import symbols and footprints according to the components which I wanted to use (and which I had at my disposal in the laboratory).
For the symbols, go to Preferences > Manage Symbol Librairies to add this and this. For the footprints, go to Preferences > Manage Footprints Librairies to add this.
In the context of Fab Labs, this library is very useful because it contains all the components we have at our disposition.
To design the schematic of the board, one should first import the right symbols. In my case, the components I listed above on this page. to do so, select the Place symbol tool, click on the page and choose the symbol you want.
R to rotate the component
C to copy it
M to move it
Delete to delete it
W to draw a wire
Then, you will have to connect the elements together. To do so, a good practice is to divide the circuit into smaller and more understandable circuits. In my case, I design the switches, LED's, capacitor, ATtiny1614, FTDI and UPDI apart. It's then easier to get a full understanding of the circuit and it's also easier to manipulate.
Don't be confused, the real design mission is for the next step, now is just about connecting parts together, and about being understandable for the community if you plan to share your design or simply for your future self.
It's always important to check the datasheet of the components you're using. In this case, the datasheet of the ATtiny1614 helped me to verify the differents connections from the chip to the components.
Now is the "tricky" part: finding the best paths, the most compact as possible while respecting the idea I had in mind. For instance, because I'm building a pomodoro timer, I want my 4 leds to be next to each other, and so has to be the resistors as well. It's about designing with constraints, something I really like, even if it took me hours to find a possible way to design my circuit.
Things I learned while designing it
always start by connecting the chip to its direct components
rotate and rotate again the components until it makes sense
the ground closes the circuit, so it's easier to end with it
just because you seem to be close to the solution doesn't mean you are really close to the solution. You don't know that until the end, when you connect the last components together
what is possible in a CAD software may not be easy to do in real life
optimize your paths and think about how you will solder the components
Preparing the files
Once your design is ready (that means that all your components are linked together), you can export your files and prepare them to be sent to the mini milling machine. I used Inkscape, gimp and fab modules to do so.
I used Fab Modules to generate the files needed by the mini milling machine using the same settings I set during the Electronics production week.
Milling and soldering
The machine I used to mill my board is the Roland MonoFab SRM-20, this machine seems very reliable, I had no problem while using it.
Soldering was fun to do, I really like doing it, even if I started with a big mistake: I was a little in a hurry, the lab was closing and I wanted my job to be done, my focus wasn't really there and I soldered the ATtiny1614 in the wrong direction. I know this little dot on the chip, which gives you the direction of the chip but I wasn't paying attention to it. What should have taken a few minutes took me over an hour: desolder a 14-legs chip isn't that easy!
I managed to unsolder the ATTiny chip with a heatgun: hold the chip in tweezers and heat the solder around the chip with a heatgun, and finally let the gravity do its job. The chip will stay in the tweezers while the board drops onto the worktable.
The heatgun can reach a high temperature and therefore burn the board, so care must be take not to heat the board for too long. Burning your precious is the last thing you want to do right now.
In order to test the board, you will need a UPDI for the communication between the board and another computer and a FTDI to program the board itself. Luckily, these are the two I already made.
The power comes from the FTDI and the data from the UPDI.
First, check if your computer recognizes the board correctly by typing dmesg -w in a terminal and see if a new device is detected when you un/plug the board. Save the ID of the board for later.
A simple blink program using the Arduino IDE is the easiest way to check if the communication is possible — and therefore if the board has been done right. Here is the one I used:
This week's group assignment is about how to use the test equipment in order to test/debug/understand electronic circuits. Because of the covid-19 situtation, I did this assignment alone, from my home.
A useful resource to understand how to use a multimeter is this tutorial from Sparkfun. It covers all the basics we should know.
The selection knob allows to set the multimeter to read different things such as milliamps (mA) of current, voltage (V) and resistance (Ω). The different positions of a multimeter are there to adjust the scale, depending on the values you are measuring.
Voltage & resistance
Voltage and resistance can be measured the same way, as they both required to be measured in parallel.
Set the multimeter to the appropriate (voltage (V) or resistance (Ω)) function. Connect the black probe to the ground (-) and the red probe to power (+). This should give you the voltage pr resistance of the circuit. If you measure it the other way around, you'll get the opposite values (negative).
Measuring current requires to connect the multimeter in the circuit, not only in parallel but in series. The current has to go through the multimeter in order to be measured.
Interupt your circuit with the two probes of the multimeter, set it to the current function (A) and you'll get the value you're looking for.
Continuity testing is the act of testing the resistance between two points. If there is very low resistance (less than a few Ωs), the two points are connected electrically, and a tone is emitted. If there is more than a few Ωs of resistance, than the circuit is open, and no tone is emitted.
This is super useful when testing a freshly milled PCB, to ensure that all paths have been cut as they should be, that there is no short in the circuit. Or later, that the components are properly soldered.