Susana Passinhas @Fab Academy 2023

Exporting the schematic SVG from KiCad

I started by going back to KiCad and double checked my schematic. I had previously made sure my clearance was 4mm (this is important to make sure the lines are not connecting and to have enough space to do the soldering).

I went ahead and added the outline cut. The outline cut will be the last thing to be cut by the machine (so it doesn't get loose while cutting the inside trace). The endmill to use for the outter cut is the 0,8mm endmill (1/32 inches) and it cuts through the board completely. So I added the outline square (white one here on the image) with a thickness of 0,8mm.

Then I just needed to export the file as an SVG so that I could edit it properly in one vector editor. To export it I selected the F.cu and Edge cuts (so I would get all the traces and outlines I needed).

Setting up the black and white per layers

I opened my files in Figma and made sure to separate them by layers, one layer for the outline, another for the trace, and another for holes. In all of them, I made sure the black parts would be what is removed and the white parts will be what is not cut (the white it's the copper that stays and allows the circuit to be conductive).

I also made sure my board design fitter the size of the board I was going to cut: 77mmx50mm. I then remembered about the resolution that I was not quite sure how to do it in Figma because a PNG is an uncompressed file, so I opened the SVG in Inkscape and checked the resolution, and set it up to 1000 so that in MODS it corresponds. The higher the resolution the better as the more detail the more precise the cut of the machine will be.

Preparing the file for the machine in MODS

Once I had all my 3 images ready (trace, outline, and holes) I opened them one by one in MODS. In MODS I right-clicked and opened programs → open program → SRM 20-MILL → PCB.

Then I started the process of preparing the images: I selected the PNG file of trace first and made sure the dpi was 1000. Then in the "mill traces" I choose the 1/64 (0,4mm), the speed is set to 4 by default and that was the speed I used. In the job height I used also the default value of 2. The offset was 4 - the default value.

Then in the "absolute coordinates", I just wanted to make sure the "origin" x,y, and z were set to 0 and in the "move to origin" the x, and y were 0 but I set up the z to 15mm, to make sure that when the endmill is moving between points it doesn't scratch the PCB.

To end the process I just toggle on the "edit/delete" and click "Calculate". I also made sure I took a look into the trace to see if there weren't any weird lines overlapping.

For the holes and the outline I used the 1/32 (0,8mm) endmill instead. For the 1/32 endmill I used the default job height of 2 and the default speed of 4. The offset was 1 - the default value. Once we click "Calculate" the software downloads the image in a format that the SRM 20 understands - the .rml format.

Calibrating the machine and setting up the correct endmill

I started by passing a brush on the bed of the machine to clean all the dust and remove anything that might impact the cut. Then I choose the first endmill I was going to use. It was the 1/64 (0,4mm) to do the traces. I used the little key to help lock the endmill to the endmill holder.

I used a FR1 board (1 side copper) with a dimension of 77mmx50mm. I used double side tape glue to stick it to the bed of the machine.

I started by calibrating the x and y, so I moved the endmill to the 0 coordinates of x and y. Then I set up that position as the 0,0 (origin). After that I calibrated the z, this one is a little bit different since we don't want it to scratch the board while positioning it. So I drop the endmill close to the board and then used the key to loosen it a bit the endmill until it touches the board. I then set the z origin (0). Before doing anything else I moved the z position up to make sure it wouldn't scratch anything.

Then I had to add the file for the machine to cut (trace image first). I clicked "cut", then uploaded my image in the format the machine understands (rml), then I just pressed "output" and the machine started to cut.

Milling

I first cut the trace, using a 1/64 endmill. When it was finished I replaced the endmill to a 1/32 and added the holes file. I did the same process as before to calibrate the machine again but this time only for the Z position. Then I did the same but this time for the outline. With this sequence, we make sure there aren't any loose pieces on the machine.

The result...

After the first cut was finished I cleaned and dusted and realized there was something strange, it seemed that in some places the machine didn't cut so well because I still could see the copper (it might be some dust for example). So I repeated the entire process again and this time it came out well!

The components

Before starting the soldering I grabbed all the components I needed for my board. I double-checked Kicad to make sure of the components I needed.

List of components 1x USB B Mini 1x Microcontroller ATSAMD11C14A_SSUT 1x Voltage Regulator 3.3v 100ma LM3480 1x LED (Light Emitting Diode) 1x Voltage Regulator 4990 ( 499Ω ohms for the LED) 1x Voltage Regulator 1002 (10kΩ ohms for Button) 1x Button Omron B3SN 6.0X6.0mm 1x Connector Pin Head SWD 2x02 1x Pin Head 1x08 1x Capacitor 2.2 UF 16v (later realized SAMD 11 recommends 1UF so I changed it...)

About the capacitors and voltage regulators:

A capacitor is an electrical component that draws energy from a battery and stores the energy. So it stores energy until is needed to be released. Using a 2.2 uF means it is safe to use this capacitor upto 400v. We are using 5v in our DC board.

A voltage regulator is a system designed to automatically maintain a constant voltage. This is used so that the LED and the Button don't burn (shortage) the board.

Soldering

Before I start to solder in my board I decided to practice on an old board. I worked with a temperature of 350 degrees and make sure to clean the tip of the soldering iron frequently.

Then I was ready to solder my board. So I started with the SAMD 11 first because it was in the center and it was more complex due to the tiny legs. I continued and then realized I had soldered the SAMD 11 reversed...So I needed to un-solder it. I used the removal wire we have to remove the biggest part of it, but still was not coming out completely, so with some help, I used the heat gun to heat up the SAMD 11 and pulled the component out with the claws. Because of this, some wires got erased, so I re-soldered again the SAMD 11 and had to connect jumpers.

Checking if the circuits were working

I used the multimeter to make sure all the connections were working. To do this I simply used the bip function and then connected the wires to my circuit making sure the current was passing on the places it was supposed to pass.

Bootloading the SWD board first

At the Fab Lab we have already a SWD D11C that can act as a bootloader (a programmer). So I used it for the new one I just had soldered.

So, to start I needed a wire to connect both SWDs, the connector at the lab has 6 wires but we only need to use 4, so we need to make sure to use the same 4 ones. Also the PCB board is a little thin for the USB so I added a piece of paper to make it fit properly.

Then, for the code I went to the page with all the information we need to follow. Then I downloaded the binary file that will make the board a programmer - free dap. To flash the board we also need the edbg (edbg is a software that allows us to program the board). I choose the latest version of the edbg for my mac and downloaded it.

Then I opened the terminal and used the command "./edbg --help" to see what options I have with this file, but the terminal replied with "permission denied". So I went ahead with the option to flashing on MacOS...

Using openocd (MacOS) instead of edbg

When the edgb firmware doesn't work on MacOS we can use OpenOCD. I used Homebrew to install OpenOCD using the command "brew install openocd". Then I created a new directory with the downloaded configuration files for the Open OCD and also added the free dap (previously downloaded) file there. Then I used the terminal to navigate to the directory and run the command "openocd".

Getting the SWD bootloaded

I tried a couple of times doing the bootloader and it was not working at first because the computer didn't recognize the new board (had no problems with the board I was using to bootload it). Then after improving the soldering and trying again, it was possible to burn the bootloader into the SWD board I manufactured and now I could use it as a programmer for my own board. At this moment I also realized I had a LED reversed (was not connecting the GND to the GND), so also update that.

Making my own board programmable

So now that I had my own bootloader I could flash my own board. So I used the same 2x2 IDC connector, keeping the orientation consistent (so that the ground marks are on the same wire). This time I needed to change the pinheads from the SWD, so instead of being the bootloader pins I used the programmer pins (the ones close to the edge of the board) and connected them to my own board.

To program the board we now needed to use a different file, so I went ahead and downloaded it into a new directory. Then I needed to open the terminal and after navigating to the correct directory using the command "openocd".

It seemed like the board was programmed but I couldn't recognize it in the Arduino IDE...so I went ahead with the help of the instructors to try to debug it by double-checking the connections with the multimeter, re-soldering components, making sure they were well soldered and nothing... I spend quite some time on this. Then I decided to go back to kicad and double-check everything.

Trying to program it!

So the good news was that now the board seemed to be recognized by the computer! So I went ahead and sent the code (SAM BA file) to make the board programmable using the SWD board I have done before.

The bad news was that in my MAC I still couldn't see the board in the Arduino IDE...So I tried in a colleague's Windows and it was recognizable (on and off) so it seemed maybe the soldering was not working so well or maybe there was a shortage... Which actually ended up being the case!

With the help of FabLab instructor, we soldered a new SAMD 11 and removed the piezo sensor as it might be doing some shortage (and it was! since without it the MAC recognized the board and with it it didn't). Without the piezo sensor on the board finally, after a few boards, a lot of debugging, and soldering the board was working! Arduino IDE recognized it and I could send the code when pressing the button to light up the led! What a moment of joy!!!!