Electronics Production

Week 8

The objective for this week was to make and test a microcontroller development board that you designed. This involved creating a PCB using one of the various methods available in our laboratory: milling with the Roland SRM-20, laser engraving with the xTool F1 Ultra, or using a vinyl cutter with the Brother machine.

For this task, I used the multipurpose PCB that I previously designed in week 6. I chose to work with the Roland SRM-20 because PCB milling is an excellent technique; this machine is capable of handling all the necessary processes: engraving the traces, drilling the holes, and cutting the board shape. Additionally, I will also demonstrate the creation of a flexible PCB made using the vinyl cutter.

Group Assignment

Check here the group assignment for this week for more information about the characterization of the design rules of the PCB milling machine.

Outputs

Here is the PCB I previously designed in week 6, in case you want to see a bit of the workflow where I created it. I made some small changes, as I needed to adjust the trace width to 0.5 mm to make it possible to manufacture on the Roland SRM-20.

Fig 1. PCB

To generate the manufacturing documents for producing the PCB on the MonoFab, we need to export the Gerber files from the software where the PCB was created. In my case, I use Altium Designer.

To export the Gerber files, go to File, then Fabrication Outputs, and select Gerber Files.

In this section, you must select the layers you want to generate in the Gerber files. It is also crucial to configure the units to millimeters.

To generate the documentation for the holes, go to the Fabrication Outputs menu and select NC Drill Files.

Once everything is ready, the necessary documents will be generated and saved in the Project Outputs folder where your project is stored. To generate the PNG files, we use the Gerber2PNG website.

You upload the documents generated in the Project Outputs folder here, and you will be able to see a preview of the PCB.

In this section, you can select which specific documents you want to generate.

From there, you can generate the PNG and download the documents.

Here are the results of the PNG files I generated.

Mods CE

To make our PNG files compatible with the Roland SRM-20, we need to convert them into .rml files. We use the Mods page to process the images and generate the toolpaths required for the monoFab.

Program

To select the correct program, open the Programs on the upper-left menu. Scroll down to find the SRM-20 mill section and select mill 2D PCB.

Workspace

This is the Mods workspace. It might look a bit complicated, but it's actually very easy to use once you follow a few simple steps.

Read PNG

First, we need to select our PNG or SVG file. Remember that the program will preserve everything in white and mill away the areas marked in black.

PCB defaults

Next, you need to select the PCB defaults. You can choose Traces (1/64) for engraving, Cutout (1/32) for cutting the board's edge, or Drill (1/32) for drilling holes.

Mill raster 2D

We need to set the tool diameter, cut depth, and the number of offsets. Once configured, we click "calculate" and then "view" to visualize the toolpath.

3D View

After clicking Calculate, a new tab will open with a 3D preview of the toolpath. This helps you verify that everything is correct before you start the milling process.

Speed and Origin Configuration

Next, we need to set the cutting speed. It is crucial to set all coordinates (X, Y, and Z) to the 0 origin to ensure the milling process starts exactly at the designated origin point.

Save rml file

Finally, we must enable this (on/off) option. Once we click calculate, the .rml file will be automatically generated and downloaded.

❮ ❯

Here are the settings I used for each stage

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Drill Process

VPanel

Once we have generated all the rml files, the next step is to begin the cutting process using VPanel, the software that controls the Roland machine.

This interface lets us move the tool along the X, Y, and Z axes using the on-screen buttons. Once the tool is at the starting point, we use Set Origin Point to save our coordinates. You can also adjust the Cursor Step to control the movement increment.

Fig 2. VPanel

After setting the origin for all three axes, we raise the tool to a safe height to avoid collisions. Then, go to the Cut menu and select your file. Simply click the Output button to begin the milling process.

Fig 3. VPanel output

PCB Fabrication

To start the PCB process, we need a sacrifice bed in case the tool cuts through the copper board. We must secure the copper plate to the sacrifice bed using double-sided tape. Make sure the tape covers the entire surface to prevent the board from lifting during the milling process.

These are the tools I used for the PCB fabrication:

Traces: 0.4 mm V-shaped 60° tool
Holes: 0.8 mm end mill
Outline: 1.0 mm end mill

Secure the sacrificial bed in the MonoFab using screws, making sure they are tightened uniformly. A perfectly level surface is essential; any tilt or warping can lead to uneven cutting depths, potentially damaging the traces of the PCB.

The first step is drilling the holes, as the copper plate is most stable at this stage, allowing for more precision. This is followed by the engraving, and the final step is the outline cut to separate the board.

This is how the board looks after all the machine processes are completed.

Final Result of the machining

I used sandpaper to improve the PCB quality because the engraving tool was a bit dull, which left some burrs. Make sure the tools you use are sharp to ensure a much cleaner result from the start.

Fig 4. PCB Result

I used a digital microscope to check the quality of the traces and the machine's work in detail.

Welding Process

Once the PCB is manufactured, we move on to the soldering process to assemble all the electronic components. For this project, I used SMD components in the 1206 size.

Components

1x XIAO RP2350
1x 10µF Capacitor
1x Green LED
1x Orange LED
1x Red LED
3x 330 Ω Resistors
1x 10 kΩ Resistor
1x Push Button
4x Header Pins

Before soldering the XIAO RP2350, it is crucial to insulate the bottom part of the microcontroller. Since this board has several exposed pads on its underside, they could accidentally touch other parts of the circuit and cause a short circuit. To prevent this, I applied a small piece of tape to the bottom of the XIAO before mounting it.

Welding

This is the final result of my soldered PCB.

Fig 5. Soldered PCB

Here is a close-up of the solder connections using the digital microscope.

Final result

To test the PCB, I used the following simple code to make the LEDs light up.

Test Code

 
                const int led1 = D9; 
                const int led2 = D10; 

                void setup() {
                pinMode(led1, OUTPUT);
                pinMode(led2, OUTPUT);
                
                digitalWrite(led1, HIGH);
                digitalWrite(led2, HIGH);
                }

                void loop() {
                }

Fig 6. Final Result PCB

Flexible PCB

To test another method of PCB fabrication, I used a flexible PCB approach. This process involves copper tape and a vinyl cutter. I recommend using a canvas fabric, as it is much more heat resistant during the soldering process compared to plastic based materials, which melt very easily.

Fig 7. Schematic

Fig 8. 3D View

I implemented an ATtiny microcontroller with several LEDs and push buttons to allow for flexible programming and testing.

I exported my document as a PDF to later convert it into an SVG using Inkscape. This allowed me to prepare the file for use with the vinyl cutter.

Code

 
            
                const int LED1 = 0;
                const int LED2 = 1;
                const int LED3 = 2;
                const int BOTON1 = 3;
                const int BOTON2 = 4;

                int estadoBoton1 = 0;
                int estadoBoton2 = 0;
                int estadoAmbos = 0;

                unsigned long lastDebounceTime1 = 0;
                unsigned long lastDebounceTime2 = 0;
                unsigned long debounceDelay = 50;

                unsigned long lastBlinkTime = 0;
                bool ledState = false;

                const unsigned long blinkInterval = 100;

                void setup() {
                pinMode(LED1, OUTPUT);
                pinMode(LED2, OUTPUT);
                pinMode(LED3, OUTPUT);
                pinMode(BOTON1, INPUT);
                pinMode(BOTON2, INPUT);
                }

                void loop() {
                int lecturaBoton1 = digitalRead(BOTON1);
                int lecturaBoton2 = digitalRead(BOTON2);

                if (lecturaBoton1 == HIGH && lecturaBoton2 == HIGH && (millis() - lastDebounceTime1 > debounceDelay) && (millis() - lastDebounceTime2 > debounceDelay)) {
                    lastDebounceTime1 = millis();
                    lastDebounceTime2 = millis();
                    cambiarEstadoAmbos();
                }
                else if (lecturaBoton1 == HIGH && (millis() - lastDebounceTime1 > debounceDelay)) {
                    lastDebounceTime1 = millis();
                    cambiarEstadoBoton1();
                }
                else if (lecturaBoton2 == HIGH && (millis() - lastDebounceTime2 > debounceDelay)) {
                    lastDebounceTime2 = millis();
                    cambiarEstadoBoton2();
                }

                controlarLEDs();
                }

                void cambiarEstadoBoton1() {
                estadoBoton1++;
                if (estadoBoton1 > 2) {
                    estadoBoton1 = 0;
                }
                }

                void cambiarEstadoBoton2() {
                estadoBoton2++;
                if (estadoBoton2 > 2) {
                    estadoBoton2 = 0;
                }
                }

                void cambiarEstadoAmbos() {
                estadoAmbos++;
                if (estadoAmbos > 2) {
                    estadoAmbos = 0;
                }
                }

                void controlarLEDs() {
                if (estadoAmbos == 2) {
                    unsigned long currentTime = millis();
                    if (currentTime - lastBlinkTime >= blinkInterval) {
                    ledState = !ledState;
                    lastBlinkTime = currentTime;
                    }
                    digitalWrite(LED1, ledState);
                    digitalWrite(LED2, ledState);
                    digitalWrite(LED3, ledState);
                }
                else if (estadoAmbos == 1) {
                    digitalWrite(LED1, HIGH);
                    digitalWrite(LED2, HIGH);
                    digitalWrite(LED3, HIGH);
                }
                else if (estadoBoton1 == 2) {
                    unsigned long currentTime = millis();
                    if (currentTime - lastBlinkTime >= blinkInterval) {
                    ledState = !ledState;
                    lastBlinkTime = currentTime;
                    }
                    digitalWrite(LED1, ledState);
                    digitalWrite(LED2, ledState);
                }
                else if (estadoBoton1 == 1) {
                    digitalWrite(LED1, HIGH);
                    digitalWrite(LED2, HIGH);
                }
                else if (estadoBoton2 == 2) {
                    unsigned long currentTime = millis();
                    if (currentTime - lastBlinkTime >= blinkInterval) {
                    ledState = !ledState;
                    lastBlinkTime = currentTime;
                    }
                    digitalWrite(LED2, ledState);
                    digitalWrite(LED3, ledState);
                }
                else if (estadoBoton2 == 1) {
                    digitalWrite(LED2, HIGH);
                    digitalWrite(LED3, HIGH);
                }
                else {
                    digitalWrite(LED1, LOW);
                    digitalWrite(LED2, LOW);
                    digitalWrite(LED3, LOW);
                }
                }

Fig 9. Flexible PCB Bracelet

Files

You can download the files created and used during this week here:

📄 Files.zip

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