6. Electronics Design
Assignments
Here you can find a recording of the lecture from the 26th of february.
This week's assignments and learning outcomes, see here:
Group assignment:
- Use the test equipment in your lab to observe the operation of a microcontroller circuit board (as a minimum, you should demonstrate the use of a multimeter and oscilloscope)
- Document your work on the group work page and reflect what you learned on your individual page
You can find the documentation for our group assignments here.
Individual assignment:
- Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller
Questions to be answered/from Nueval:
Have you answered these questions?
- Linked to the group assignment page
- Documented what you have learned in electronics design
- Checked your board can be fabricated
- Explained problems and how you fixed them
- Included original design files (Eagle, KiCad, etc.)
- Included a ‘hero shot’
Hero shot
Hero shots from the group assignment
Raspberry Pi Pico measured with the Multimeter and the Oscilloscope
Operating voltage 3.3V - Raspberry Pi Pico 3.3V
Operating voltage 5V - Raspberry Pi Pico V-bus
Oscilloscope - Raspberry Pi Pico programmed to change colours on a Neopixel LED
Hero shots from the individual assignment
A 3D model of the development board for ATtiny412.
A 3D model of the development board for Raspberry Pi Pico.
Summary
This week, as a group, we used the test equipment in our lab to observe the operation of a microcontroller circuit board by using a multimeter and oscilloscope. We documented the results on our group page and you can find it here. I was responsible for measuring the Raspberry Pi Pico with the Multimeter and the Oscilloscope.
In the the individual assignments I explain how I designed a circuit board with ATtiny412 in Pre-Fab. Then I designed a circuit board with the Raspberry Pi Pico and a LED. I used KiCad as the EDA tool. I installed the Fab Lab library in the KiCad program. I used the library for symbols, footprints and 3D models of components from the Fab Inventory.
Work process detail
Designing a circuit board with ATtiny412 in Pre-Fab
I attended Pre-Fab this fall and did some projects in advance. Here you can see my Pre-Fab website. I describe what I did here below.
Done with directions from Andri Sæmundsson
Andri Sæmundsson made a series of videos for Fab Lab Reykjavík, where he explaines all the steps in producing a circuit board with ATtiny412. I followed his directions and here I describe every step I took.
KiCad setup
The first part
In the first video he explains how to set up KiCad 8.
On KiCad.org I downloaded the KiCad program and then installed it on the computer. On the About KiCad site it says that KiCad is an open source software that can be used to design EDA or Electronic Design Automation. In KiCad Schematic Editor is used to draw electronic circuit and you have access to thousands of symbols that can be found in libraries. The PCB Editor is then used to add elements to the circuit. Then you can use the 3D viewer to preview your design.
I opened the program, clicked on File and new to create a new project. I saved it in a folder in my computer. When saving a new project there will be two files created, Schematic file and a PCB file. I began by editing the Schematic file.
Schematic and PCB files
When saving a new project there will be two files created, Schematic file and a PCB file.
Hiding libraries and adding Fab Lab library
The second part
In this video he explains how to hide librarys that are seldom used and add a KiCad library.
After watching the video I googled "Fab Lab library", as suggested in the video, and downloaded this library. Then I clicked on the button marked as Code and chose Zip. Then I opened up the downloads folder and extracted the library. I saved this library in a folder where I plan on storing everything connected to working with KiCad. The next step was to open KiCad, click on Preferences and Manage Libraries. This photo shows that there are many libraries and it can be hard to find the right library, so as Andri Sæmundsson mentioned in the video, it would be easier to work with a few libraries, but first I had to install the Fab Lab library before removing other libraries.
I clicked on the small button with a folder sign on it, opened up the folder with the library and double clicked on the sym file.
Inline blocks
Here you can see the tiny folder sign.
Then I clicked on Preferences and chose Footprint Libraries. I clicked on the Folder button and this time I added the Fab.Pretty folder.
After adding the Fab Lab library to the lists of libraries I took the clicks away from the box under Active in front of every other library. After that the only active library is the Fab Lab library.
Designing the circuit in Schematic Editor
Third, fourth and fifth part
In these three videos; first part, second part, third part he explains how to use Scematic editor.
Adding elements from Fab Lab Library
In the Schematic Editor, to add an element from the Fab Lab Library you either click on the symbol here to the right or you just click on the letter A on your keyboard.
I wrote ATtiny 412 and chose it from the list. To the right I could see the symbol for this microcontroller and below it there was an footprint image of it. Then I clicked ok. I could drag it around and I placed it on the screen by leftclicking on the screen. To add a switch I opened the library again and wrote Switch and chose Switch_Tactile_Omron from the list. In the information text below I could see the letters SMT. SMT means that the button should be surface mounted.
After that I added a capacitor with the number C_1206. Then I added a Led with the same number as the capacitor; L_1206.
The last element that I added was a Conn_PinHeader with three male pins in a row.
Because the icon for the library is chosen, each time I click on the screen the library opens. To be able to use the mouse I had to click on the arrow at the top of the list. Then I could use the mouse to move elements around.
To rotate an element you can write R and then the element rotates 90 degrees.
Elements can be labeled by clicking on the symbol marked with an underlined A or just writing the letterL. I added a label marked GND to Ground and another one marked VCC to VCC. I labelled pin 6 as UPDI. I labelled pin 7 as LED and also put a LED label on the resistor. Then I connected the other end of the resistor to the LED with wire.I labelled the other end of the LED with GND.
I labelled one end of the capacitor with GND and the other end with VCC. I labelled one end of the switch as GND and the other one as BNT.
The first pin on the PinHeader I labelled as VCC and the second one as GND. Pin nr. 3 was labelled as UPDI.
I connected the led to pin 7, which is marked as PA3. Then I connected the LED to Ground. Then I connected the switch to pin 2, which is marked as PA6. In Schematic Editor it looks as if Pins nr. 2 and 7 are on the same side but when you look at this photo of ATtiny 412 from Spence Konde you can see that the pins are on each side.
I connected the first pin on the Conn_PinHeader to Ground, the second one to VCC and the third one to UPDI.
I used the Electrical Rule Checker to see if everything was legal but got a few errors. After marking pins nr. 3, 4 and 5 with No connection flag and putting a power flag on Ground and VCC, the Electrical Rule Checker and everything seemed to be okay.
In Page settings I changed the page size to A5 and added some information about the project. Then I added a text box, just to try it. I also put a rectangular frame around some of the elements and changed the style of the frame.
First Schematic Editor, then PCB Editor
Sixth part
This video explains how to use the PCB editor.
Before opening the PCB editor I changed the value of the capacitor and the resistor by clicking on each of these element and then clicking on the symbol for Properties. Another way to open the Properties manager is to right click on an element and choose the Properties manager from the list. The third way is simply to write the letter E and the fourth way is to double click on the text. I changed the value of the Capacitor from C_1206 to 1 uF, the value of the Resistor from R-1206 to 1k. Then I opened the PCB Editor by clicking on the symbol for it in the top bar.
To fetch the elements from the Schematic Editor I clicked on Update PCB Editor from Schematic. Then a window popped up and I clicked on the Update PCB button.
In the PCB Editor you can see different layers at the right side of the window, choose those layers you want to work with and hide all others. I was working with the top layer of the electric board and therefore I chose the F.Cu, or in other words; the front of the copper plate. Then I could hide the view of the backside by clicking on the eye in front of B.Cu. I hid all layers except the layers for Edge.Cuts, F.Courtyard and .... The F.Courtyard shows a violet frame around elements and it shows how close you can lay wires to elements, f.ex. if you cross the violet frame you are too close to an element.
I changed the setup of the pins by editing the labels in Schematic Editor; Pin1 changed from VCC to UPDI and Pin3 changed from UPDI to VCC. Then I clicked on Update PCB Editor from Schematic.
I could see that some of the blue lines, which showed how the electric circuits would be connected, were crossed. To fix that I rotated elements.
When organizing the board I had to make sure that I wouldn´t make the circuits too thin and that there is enough space for the bit to mill the traces while making sure that there is enough clearance. In Board Setup I went to Design rules and wrote that mininum clearance, minimum track width, minimum connection width, minimum annular width and copper to hole clearance should all be 0.4mm.
To connect the elements/making tracks for the circuits that I wanted to mill, I clicked on the Route Tracks symbol and began drawing tracks between footprints. I made sure that the lines were straight when entering footprints. I used the Route tracker to mark all circuits that had to be milled, as can be seen in this photo.
To see what the board would look like I clicked to the 3D viewer and saw that Kicad made no extra space around the circuit, so I chose the Edge.Cut layer, clicked on the rectangular symbol and drew a rectangle around the circuit, giving it more space around all elements. This is what it looked like in 3D view after that.
3D models added and then inspected in 3D viewer
Seventh part
In this video he adds 3D model to his PCB and uses the 3D viewer.
To add 3D models to my board I right clicked on each element, chose properties and then clicked on 3D models in the top bar. It is also possible to click on the letter E on the keyboard. Then I had to click on the line that was lighted up with blue because then a small folder logo appeared beside the text. After that I clicked on this small folder symbol, searched for the Fab Lab Library and opened it. In it I found the Fab.3Dshapes folder and opened it to find R_1206.step and finally click on OK. When I opened up the 3D viewer I could see that the Resistor appeared in 3D on the board.
There was no 3D model for ATtiny4012, led light and button in Fab.3Dshapes, so Andri Sæmundsson explained in the video what to do and pointed to this website to find the 3D model. I had to sign up to be able to use the website. Then I used the search window to find each element, chose the right one from a list and downloaded a 3D model. I opened the download in the downloads folder, copied it and pasted it into the Fab.3Dshapes folder. After that I could find the models in the same way as I explained before. The only problem was that when these models were opened up in Kicad-properties-3D models-Fab.3Dshapes they didn´t sit on the plate but lay on their side. That was easily fixed just by rotating them about 90 degrees.
Note
Check out if the elements you add to Fab.3Dshapes folder are at the right angle. If not, rotate the angle on x-axis.
Design Rule Checker
Eight part
Here Andri Sæmundsson shows how to finish the design of the board in PCB editor, use Design Rules Checker and finally prepare the design for milling and cutting in Inkscape.
I followed the directions on how to use Design Rule Checker to see if everything is legal. I clicked on the symbol for it and chose Run DRC. I got 6 warnings that said "Silkscreen clipped by solder mask". Andri said that it would be important to fix this if the board was to be produced, but since this doesn´t really matter when this board is made, i ignored the warnings.
To export the final desing I chose File and Export SVG. I checked in the F.Cu box and changed the Print Mode from color to black and white. Then I saved the file. The next step was to open the file in Inkscape. The whole page appeared in Inkscape with the frame around the page and the text boxes. I only needed the board, so I copied it and pasted it into a new Inkscape file. In Inkscape I changed the colour of the circuit from black to white and changed the background to black.
I had to make two files in Inskcape, one for milling the circuit and another one for cutting the outline, because these two files are cut with different bits. To make the file for the outline I copied the outline and pasted it beside the other one. Then I copied it again and pasted exactly the same rectangle, but coloured it white. In the boxes for height and width I extracted 1,6mm from the numbers by writing -1,6 in both boxes. Then I selected both rectangles, went to Object and Align and distribute. Then I aligned the rectangles on x-axis and y-axis. Now I had an outline that was 0,8mm wide and that was a good size for the cutting line because the bit that will be used is just under 0,8mm.
Finally, I saved a new Inkscape file with the outline drawing, then selected the drawing of the outline and exported it as PNG. Then I also exported the drawing of the circuit as PNG.
Low resolution
When I was going to mill the board I realized that these .png were not good enough. The resolution should be higher. I will tell you more about that later, but here below are .png in better resolution and also the Inkscape files.
Kicad files for ATtiny board
Practice
Inkscape files for ATtiny412 board
Designing a circuit board with Raspberry Pi Pico
After going through the process of designing the ATtiny412 I thought that it would be simple to do the same with the Raspberry Pi Pico, which I want to use in my final project. I wanted to try it out with two individually adressable LEDs to do some experiments with the LEDs. Here is how it went...
Videos made by Andri Sæmundsson
I followed the directions from the series of videos that Andri Sæmundsson made for Fab Lab Reykjavík , where he explaines all the steps in producing a circuit board with ATtiny412.
This is the first video in the series, but I only followed the steps from video number three and forwards.
The Schematic Editor
I opened the Kicad app and clicked on the button for adding components from library.
Footprint for Raspberry Pi Pico
This is an image of the symbol (upper image) and the footprint (lower image) for Raspberry Pi Pico in the Fab Lab Kicad Library. I chose the one called "Combined" for the RPP to be surface mounted.
The next steps turned out to be very difficult for me. When I made the ATtiny412 board, I used pins for input, output and power. The Raspberry Pi Pico has a micro-usb for these connections and I did not know how to design these connections without the pins. Connecting the single NeoPixel LEDs was also complicated for me. The thing I was having problems with was choosing the right size of a resistor. I also thought that the 1206 resistor was a certain resistor but Þórarinn Bjartur Breiðfjörð explained to me that a 1206 resistor and a 1206 capacitor can have different value.
I asked Svavar Konráðsson for assistance. He had explained the connections on the Fab Lab Ísafjörður website, but I needed more explanation. He told me to use a 1k resistor and place it between the Raspberry Pi Pico and the LEDs and connect it to the the GP0. Then to connect between the LEDs from DIN to DOUT. For power the VDD in the top LED was connected to the Vbus. Then I added a connection from the VDD on the lower LED to the connection between the other LED and the Vbus. I did the same thing with the GND; first I connected the VSS on the upper LED to GND on the Raspberry Pi Pico and then I added a connection from the lower LED to this connection.
After that I added two capacitors and placed each of them close to the LEDs. I added a connection from them to the Vbus and the GND.
Errors in the design
Three errors
When using the Design rule checker, three errors were reported.
DOUT error
This error was easy to fix. I just added a No connection flag to this pin, because I wasn't going to connect anything to it, and it told KiCad that I had not forgotten to connect anything to it.
Power flags
The Design Rule Checker complained that Input Power pin (VBUS) was not driven by any Output Power pin. The same error appeared for the GND. When I tried to add a Power symbol to these pins, the errors persisted to appear. The reason was that I did not choose the right symbol from the list. I should have chosen the Power Flag.
Finally, there were no errors and the drawing was ready.
The PCB Editor
PCB editor
Then it was time to allign all elements on a PCB board in the PCB editor. After opening the editor I clicked on the Update PCB from Schematic.
Bord Editor - minimum clearance and tracks
I clicked on the symbol for the Board Editor and clicked on Design Rules. I changed the settings as you can see here below.
Trying to puzzle
It was quite complicated to arrange all elements so that tracks were not crossing each other. It took me a long time to rotate, rearrange and wire together everything. The image below shows an image where things did not work out. There were tracks crossing each other.
If traces cross each other
I told Svavar Konráðsson about the problems I ran into after I had solved them and he told me that I could have used a 0 Ohm resistor to solve this problem, just like Neil Gershenfeld did here. The 0 Ohm creates a bridge that traces can go over and under without touching each other. Brilliant! I will keep this solution in mind if I run into such problems later on.
A long list of errors
A long list of errors
When I used the Design rules checker in the PCB editor it showed a long list of errors. I had to check out what to change.
Final drawing with too thin traces
This is the drawing I made with the lines that are too thin.
The Design rule checker also told me to connect between these two pins. I find that strange and I will ask if that is correct before connecting them. The result was that I did not have to connect them.
After asking Svavar Konráðsson and Þórarinn Bjartur Breiðfjörð for assistance, I changed the following:
I clicked on the small + sign under Tracks and added a pre-defined size of tracks. First I made it as 0.6 but changed it to 0.4.
I had to adjust the settings for constraints under Board settings to get rid of errors. These are the final settings:
I changed the outline/cutting line of the board to make the micro-usb on the Raspberry Pi Pico more accessible. To do that I clicked first on the edge.cut layer and then moved the lines. I had to turn off the silkscreen layer to get rid of error notifications, but that was ok because I didn't need that layer. I had to move components and tracks to be able to adjust the cutting line. This is the final outcome:
Adding 3D models for 3D viewer
Adding 3D models in PCB editor
I added 3D models in the PCB editor. I had to find a 3D model on the Snapeda website.
This is what the board looked like in the 3D viewer:
KiCad files for Raspberry Pi Pico
Learning outcome
Learning outcome for the group assignments
The group project was a good exercize for me in using the Multimeter and the Oscilloscope. My understanding of them is getting better but I have to practice a lot more if I want to be able to use them. I liked how the commands for different colours appeared as different looking waves in the Oscilloscope.
Learning outcome for the individual assignments
This week was quite difficult for me, even though I had been prepaired for this in Pre-Fab. It takes time to understand how each component on a microcontroller board works and how to connect them together. It also takes time to understand how to program them. I know this will all come with more practice.