<. <br>
It was fascinating to see how clearly pulse pattern shown in the oscilloscope tells you "A" in ASCII code. If you are fluent in machine language (or if not by just making a reverse-engineeing program), you can basically decode what's being communicated from change of current/volatage.
####Objective <br>
To design and mill a PCB and stuff it with components to make a microcontroller.
As I was completely new to electrical engineering, I decided to add an LED and a button to ATSAMD11C (14-pin), which turned out to be still difficult.
####Metrics <br>
**A. Designing part** <br>
* Base design: USB-D11C-serial using ATSAMD11C14 (later I realized I mixed this up with the one described in Eagle tutorial...)
* Software: Eagle in Fusion 360
**B. Milling part** <br>
* Milling machine: Roland MonoFab SRM-20
<br><img src="./3d-milling-machine-monofab-srm-20-007727795-product_zoom.jpg" alt="laser_module" width="200"/>
<br>
* Endmills: 1/64 endmill for cutting the copper, 1/32 endmill for cutting out the PCB
* Material: Single-sided copper board
* Software: mod
####Protocols and results <br>
**A. Design part** <br>
1. Pick up a basic design, onto which I put an LED and a button. I chose "hello.D11C.serial.5V.1.1" from [here](http://academy.cba.mit.edu/classes/embedded_programming/D11C/hello.D11C.serial.5V.1.1 "test"). <br>
<br><img src="./hello.D11C.serial.5V.1.1.png" alt="laser_module" width="200"/><br>
2. Draw a skematic design on Eagle.
3. Add an LED onto the skematic design. Beware of the direction.
4. Add a button onto the skematic design. I was initially wondering why not directly putting the button in between the microcontroller and the LED. I later realized it is not a physical switch that connect/disconnect wires electrically but rather a digital ON/OFF, which is why you need to connect them separately to the microcontroller.
<br><img src="./Schematic_20211013final.png" alt="laser_module" width="800"/><br>
5. Complete the routing on PCB, using zero-ohm bridges where necessary.
<br><img src="./PCB_Des_20211013final.png" alt="laser_module" width="800"/><br>
6. Export the trace design and the outer design.
**B. Milling part** <br>
1. Use the above-mentioned sketches.
2. Pick up a copper board.
<br><img src="./copper_board.JPG" alt="laser_module" width="200"/><br>
3. Put the copper board onto the milling machine. It is important to put double-sided tape so that the entire copper board sticks to the base material. In my case, somebody had done it before I used.
4. Set up a 1/64 endmill. Kevin instructed us that one of the common mistake here is to let the existing endmill fall off when you loosen the holder with screw. Holding it tight with my left hand, I carefully replace the endmill by a the one I was going to use. Another common mistake here is to set the z position of the endmill so low that it hits the base material when it starts moving from "home" position to "origin" position. I avoided it by putting the endmill up.
5. Set up the parameters (well, somebody before me did the setting). The 1/64 endmill is so small that it has to go aorund the same route for four times to make sure there is enough space for manual soldering.
6. Mill the copper layer of the circuit.
7. Switch the endmill from 1/64 to 1/32.
8. Cut out the PCB. I realized there was a tiny scar on one of the four USB routes due to the previous attempt, but I thought I could easily connect the cut part by soldering. (I was wrong)
<br>
**C. Stuffing part** <br>
1. After milling, I first cut the unneccesary copper foils with knife.
2. I soldered the components one by one. A good trick introduced by Kevin was to put a solder bit on one end of the component, place the component and solder that end to fix it to that position. This technique was quite useful especially when I was dealing with small parts.
3. Initially, I put too much solder. In this case, I used a brade to remove excessive lead.
<br><img src="./soldering_fail_1.JPG" alt="laser_module" width="200"/><br>
4. At the end, it became like a PCB!
<br><img src="./pcb_done.JPG" alt="laser_module" width="200"/><br>
<br>
**D. Confirmation part** <br>
1. Lastly, I checked if each part is properly connected. I used a digital multimeter to check the current one by one. It worked.
2. I tried inserting it to my MacBook via a USB cale, but it was not read. I am investigating the design again.
[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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