<. <br>
<br><img src="./hello.D11C.serial.5V.1.1.png" alt="laser_module" width="200"/><br> The one I did two week ago did not work, so I had to redo the schematic design.
2. Draw a skematic design on Eagle. This time, I made the board as simple as possible; for example, I did not make the wider copper layer for heat decipation or use the 5V-3V regulator with two extra capacitors, or use pullup resistor. I basically followed the simplest path i.e. putting LED and resistor in between one pin of D11C and GND, and a button in between another pin of D11C and GND.
<br><img src="./final_schematic.png" alt="laser_module" width="800"/><br>
3. Complete the routing on PCB, using zero-ohm bridges where necessary.
<br><img src="./final_pcb_des.png" alt="laser_module" width="800"/><br>
4. Export the trace design and the outer design. I did not know there was a critical mistake at this point...
**B. Milling part** <br>
1. Use the above-mentioned sketches.
2. Pick up a copper board.
3. Put the copper board onto the milling machine. Now that I am becoming used to this process, I decided to use a smaller copper board to minimize waste.
4. Mill the copper layer of the circuit (trace with 1/64 endmill and line with 1/32 endmill).
7. Cut out the PCB.
<br>
**C. Stuffing part** <br>
1. After milling, first cut the unneccesary copper foils with knife.
2. solder the components one by one.
**D. Bootloading part aka where I struggled the most** <br>
1. I used the bootloader for D11C, but the PC never seemed to be reading my chip.
There were two mistakes:
* I was initially using a wrong regulator with wrong direction; after several failed attempts to bootload this chip, I realized the component was wrong (thanks Nathan for figuring it out). I changed it to the right 3.3V regulator (1mA one).
* I thought it should work after putting a smaller one. Instead, it melted with smoke! I could not figure out at this point, but when I finally gave up and decided to make a new board design and mill it, I realized that there was small area where the 1/64 endmill could not cut, therefore shortcutting the circuit. I cut this part apart by knife and voila, it worked.
<br><img src="./comparison.JPG" alt="laser_module" width="800"/><br>
<br><img src="./too_close.JPG" alt="laser_module" width="800"/><br>
**E. Coding part** <br>
1. I used Arduino. Initially I could not install the board definition with the link `https://raw.githubusercontent.com/qbolsee/ArduinoCore-fab-sam/master/json/package_Fab_SAM_index.json`, but after several more attempts on Tuesday, it worked. (Thanks for the fix!)
2. There were a few more errors (port was not read, or it took forever to update the chip, etc.). Rob suggested that I uninstall and reinstall the IDE. After going over the same procedure written on MTM, it finally worked!
3. For the programming part, I made use of the basic design from "File" command of the IDE. I checked the mapping of the pins, and accordingly chose the port on IDE using `const int` rather than hard-code the port number every time.
<br><img src="./samd11c_image_pin_map.png" alt="laser_module" width="800"/><br>
<br><iframe width="560" height="315" src="https://www.youtube.com/embed/qmrBv4LuDsw" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><br>
[original files](https://hu-my.sharepoint.com/:f:/g/personal/ttokunari_mde_harvard_edu/Eo_MW5iJhp1GvL7Oqn-jOrYB6G4nvFlrPQ0QWN5hT0okVg?e=J0TZIo "original files") <br>
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