Week 8. Electronics production

Hero Shot

This week we were involved in exploring the PCB milling machine (SRM 20). To mill the board we used SRM 20 and used mods to generate tool path and also to convert svg or png to rml file. This is because SRM 20 reads only rml file. To operate SRM 20 we used VPanel, Vpanel is like a control software for SRM 20.

Not only that we had to do milling and ultimately program our own board. Since it was a challenging task for me because as in the first place I was partially afraid thinking that whether I will be able to mill the PCB perfectly or not without breaking any mill bits as we were having limited mill bits. Secondly whether My soldering will come upto expectation or not and finally regarding the continuity of board after soldering. But to my surprise all of them turn out to be good and upto the mark which made me happy and boosted me to move further with the week’s documentation.

Assignments for the Week

Group Assignment:

• Characterize the design rules for your in-house PCB production process: document feeds, speeds, plunge rate, depth of cut (traces and outline) and tooling.

• Document the workflow for sending a PCB to a board house.

Link to the group Assignment is here

key takeaways from this week

• Never leave the SRM 20 unattended while milling PCb and be extra carefull while handling 1/64 inch mill bits because since the profile of endmill is so tiny you will land up breaking it.

• While soldering we need to be so careful and cautious and should not keep the soldering iron more than 3 seconds on the board.

• Always try to keep the constraints value of traces to 0.39 while milling the board in order to avoid overlapping of traces.

• Try to hold your board with pcb holder so that you won’t be shaking your board while soldering.

Individual Assignment:

• Make and test a microcontroller development board.

MonoFab SRM-20 Specifications:

• Cuttable Material: Modelling Wax, Chemical Wood, Foam, Acrylic, Poly acetate, ABS, PC board

• X, Y, and Z Operation Strokes: 203.2 (X) x 152.4 (Y) x 60.5 (Z) mm

• Workpiece table size: 232.2 (X) x 156.6 (Y) mm

• Distance From Collet Tip to Table: Max. 130.75mm

• Loadable Workpiece Weight: 2 kg

• Power Requirements: Machine: DC24V, 2.5A, Dedicated AC adapter: AC 100-240 V ±10%, 50/60 Hz

• Power Consumption: Approx. 50 W

• External Dimensions: 451.0 (W) x 426.6 (D) x 426.2 (H) mm

• Weight: 19.6 kg

• Installation Environment: Temperature of 5 to 40°C, 35 to 80% relative humidity (no condensation)

• Milling Operation: Utilize a 1/64 tool for tracing and a 1/32 tool for edge cutting and drilling.

PCB Fabrication

I will use the same board that I had designed in Electronics design week. I had design my circuit board by considering all the GPIO pins and communication protocol pins which I will require while doing my final project. So henceforth What I had decided is to use the same board for my final project too.

Materials I used while milling

• 1/64” :- used for milling the traces of circuit board

• 1/32”:- used for edge cutting or boundary cutting of board

• Scrapper:- used for removing the pcb board after milling gets completed

• Double sided tape:- used for glueing the pcb board on the SRM bed

• Single sided board(PCB):- Work piece for the assignment

• Vacuum cleaner:- for cleaning the chips produced while milling

• Soldering iron, soldering lead and flux, soldering iron stand and pcb holder:- for soldering the components together

• Tweezer:- for picking and placing the tiny components while soldering

As I had already designed my circuit board comprising of Xiao RP2040 as my microcontroller. I directly exported the SVG file format of both front copper layer(F.CU) and its edge cut(B.CU) from my Week 6 assignment to SRM 20 for milling.

Using Mods

• MOD is a software developed by MIT for easier use of different machines like Roland vinyl cutter, SRM milling machine, 3D printers. In addition to that it is also used to generate tool path for the traces and edge cut of our pcb in SRM 20. In our lab we use SRM 20 for PCB milling

I pressed on the power button of SRM 20 to start milling my board

Steps to follow while using Mods

• Open the mod and right click on it and open the program

• Open the mill 2d pcb and select the SVG file that you want to do milling

• Invert the image, select the endmill from the list and calculate the traces to see its milling path

Try keeping the XYZ value to zero before downloading the rml file

• Download the rml file which is like a gcode file for SRM 20 while we do milling

• For the edgecut select the SVG file, select the endmill as mill outline and calculate and view its path for milling

• Download the rml file for edgecut by enabling the download option

• Start doing XY and Z homing for the SRM 20 by opening the V-panel

• Do calibration of XY and Z by chosing the origin and setting their values to zero.

While doing Z calibration using paper, I ensured that the tip of endmill doesnot just touch on the surface of paper making z calibration incorrect. So for that I pressed my endmill little bit more on the coper board and made z zero.

• Upload the rml file and start milling the board. For that go to cut > Add > select the rml file by deleting all the previous files > output

• I cleaned all the surface after I completed milling

• This is my first milled circuit board in which some of the traces were overlapping with each other because I had kept constraint as 0.37. Next I changed constraint to 0.39 and done slide changes with arrangements of pins in schematic diagram and did milling for second time.

first circuit board

After that I went for milling my second board and after I finished milling;

• I checked the continuity of my board,

second circuit board

These are the list of components that I will be using while soldering my pcb

• I start soldering the components which I had gathered together for my board

Short video showing how I did soldering of my components on the board

• This is how my PCB looked like after I finished soldering all the components on it. I connected the board to laptop with USB cable and found that the LED is blinking which means my circuits are correct.

• Next I wanted to program my board so for that I opened the Arduino IDE and installed the XIAO RP2040 board package, for that go to file > preference > in “additional boards manager urls” add this link and click ok

  https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json

• Go to tools > Board > Boards manager, search for XIAO RP2040 and install it

• The packages will start downloading

• Go to tools > Board > Raspberry pi RP2040 boards and select Seed XIAO RP2040

I tried connecting LED using bread board, jumper wires, resistor with my development board

Short simulation video showing LED blinking with my development board

I connected the anode (longer leg) of LED to the GPIO pin No 2 (D2) through the resistor and cathode (shorter leg) to the ground (GND)

Code which I used to run the program

const int ledPin = D2;  // Use D2 as the LED pin

void setup() {
pinMode(ledPin, OUTPUT);  // Set D2 as an output pin
}

void loop() {
digitalWrite(ledPin, HIGH);  // Turn the LED on
delay(1000);                 // Wait for 1 second
digitalWrite(ledPin, LOW);   // Turn the LED off
delay(1000);                 // Wait for 1 second
}

I even tried blinking test for the inbuilt LED of my development board which is connected to pin D0 for which I had used the same code mentioned above. I compiled the code and uploaded it in the arduino IDE to see the simulation.

Files for the week.

• RML files for SRM 20

• SVG file for traces and edge cut

It was really nice in learning how to do soldering and at the same time running simple programg with our own board was even more fun and worth learning which is very important as we approach further for the final project.