8. Electronics Production

XIAO ESP32-C3 Development Board

This week I made and tested a microcontroller development board that I designed in Week 6. The workflow covers PCB layout export, G-code generation in Mods CE, CNC milling on the KEXU machine, component soldering, and functional verification. I also participated in the group assignment to characterize our lab's in-house PCB production process.

Group Assignment

As a group we characterized how PCBs are made at Chaihuo — both in-house on the KEXU CNC and through a board house (JLCPCB). We tested machine parameters, documented the milling workflow, and compared milled vs. manufactured boards.

Week 8 Group Assignment — Chaihuo Fab Lab

What I learned from the group work

Topic	Key takeaway
Design rules	In-house milling needs ≥ 0.38 mm trace/space. Wider power buses are more reliable than thin signal traces after milling.
Z zero	A board that is not flat or a Z zero that is slightly off produces shallow traces or cuts into the sacrificial layer. The paper-drag test is critical.
Mods workflow	KiCad Gerber → PNG → Mods CE → G-code bridges design and the CNC controller. Always simulate before cutting copper.
Browser choice	Use Chrome or Edge with Mods. Some browsers produce bad toolpaths with unwanted dots.
Post-milling	Clean the board (scrape loose copper, wash off FR-4 dust) before soldering — oils and dust cause bad joints.

CNC Machine for Electronics Production

Last week I studied CNC machining on a larger machine. The same principles — fixturing, tool selection, origin setup, and G-code execution — apply to the smaller CNC mill we use for electronic production.

At Chaihuo Fab Lab I milled my board on the KEXU (刻序) benchtop CNC. PNG images are exported from KiCad Gerbers, toolpaths are generated in Mods CE, and the resulting .nc files are loaded directly into the machine controller.

Tools used for this board

Operation	Tool	Notes
Trace isolation	40° #502 V-bit	Only V-bits in our lab inventory are suitable for PCB tracing
Outline cut	1.5 mm ball-end mill	Used to cut the board free from the copper-clad sheet

Preparation — Components & Circuit

I designed this development board in Week 6, using the Fab Academy KiCad library. The carrier hosts a Seeed Studio XIAO ESP32-C3 with breakout headers, a push-button, and LEDs for I/O testing.

Bill of materials

Component	Quantity	Ref on board
Seeed Studio XIAO ESP32-C3	1	U1
CONN HDR 6POS 0.1" TIN SMD	2	J1, J2 — left & right pin breakouts
Tactile Switch SPST-NO Top Actuated SMD	1	SW1
LED 1206 SMD	2	D1, D2
RES 1 kΩ 1% 1206	2	Current-limiting resistors for LEDs
RES 10 kΩ 1% 1206	1	Button pull-up (revised design)

G-code Generation in Mods CE

I followed the Mods CE PCB milling workflow to go from KiCad design to CNC toolpaths. PNG images are required because they are lossless — JPEG compression can break fine trace geometry.

Step 1 — Export Gerber from KiCad

1. In KiCad PCB Editor: File → Fabrication Outputs → Gerbers.
2. Selected F.Cu (front copper) and Edge.Cuts (board outline).
3. Exported the front copper and edge-cut Gerber files.

KiCad fabrication output — selecting layers for Gerber export.

Step 2 — Convert Gerber to PNG

1. Uploaded the Gerber files to Gerber2Png.
2. Set up the trace layer and edge layer, then exported PNG files.
3. Verified that traces appeared as white lines on a black background (correct polarity for Mods).

Gerber2PNG — upload Gerber files and configure layer export.

Exported traces_toplayer_0.png and outline_toplayer_2.png ready for Mods.

Step 3 — Generate toolpaths in Mods CE

1. Opened Mods CE in Chrome → right-click → program → Open Program.
2. TRACES — This tool works with both SVG (top section) and PNG (bottom section). I used PNG. Click select png file and select traces_toplayer_0.png.
3. The traces image appears in the preview window.
4. Set the PCB milling preset to 40°#502 V-bit.
5. Enable file output by turning the On/Off toggle ON.
6. In Mill Raster 2D, click calculate to generate the G-code.
7. Review the 3D preview simulation to verify the toolpath.
8. Click save file to download traces_toplayer_0.png.nc.
9. Outline pass: reloaded Mods, loaded outline_toplayer_2.png, set ball-end / end-mill parameters → Calculate → saved the outline file.

Mods CE — PCB milling preset and Mill Raster 2D configuration.

3D preview of the trace isolation toolpath before saving the G-code file.

Machine parameters used

Parameter	V-bit (tracing)	Ball-end mill (outline)
Feed speed	4 mm/s	4 mm/s
Spindle speed	14,000 rpm	14,000 rpm
Offset number	4	4
Offset stepover	0.2 mm	0.2 mm
Cut depth	0.23 mm	0.45 mm
Tool	40° #502 V-bit (0.3 mm effective)	1.5 mm ball-end mill

CNC Setup & Milling

Fixturing the copper board

1. Placed the single-sided copper-clad board (1.6 mm FR-4) on the sacrificial wooden backing plate.
2. Secured it with double-sided tape and checked that the board was flat across the work area.

Tool change & zeroing

1. Installed the V-bit for tracing and tightened it with the provided wrenches.
2. Set X/Y at the front-left corner of the copper board.
3. Set Z using the paper-drag test — lower until the bit just scratches the tape, then set Z = 0.

Installing and tightening the milling tool inside the KEXU CNC work chamber.

Copper-clad board secured on the sacrificial layer, ready for origin calibration.

Start milling

1. Loaded traces_toplayer_0.png.nc from USB (FAT32, no hyphens in filename).
2. Moved the tool above the origin point before pressing start.
3. Ran the trace program first at 14,000 rpm spindle speed.
4. Swapped to the ball-end mill, re-zeroed Z, loaded the outline G-code, and cut the board free.

PCB trace milling on the KEXU CNC — V-bit isolating copper traces on the development board.

Post-processing

After milling there were burrs on the board surface. I removed them with sandpaper, then washed the board with soap and water to remove oils and FR-4 dust before soldering.

Problems and How I Fixed Them

Revised circuit — pull-up resistor correctly connected to the button input.

Soldering

After milling and cleanup I soldered all components onto the board. I worked at the Fab Lab bench with a fume extractor, multimeter, and fine-tip soldering iron.

1. SMD passives first: resistors, LEDs, and the tactile switch — tacked one corner, then soldered remaining pads.
2. Headers: inserted both 1×6 pin headers, tacked one pin each for alignment, then soldered all pins.
3. XIAO module last: placed the ESP32-C3 on its castellated pads, aligned the USB-C port flush with the board edge, and soldered each pad carefully.
4. Inspection: checked all joints under magnification for bridges and cold joints.

Preparing SMD components and the milled board at the soldering station.

Soldering the XIAO ESP32-C3 module — tweezers are essential for positioning small SMD parts.

Milled board after soldering all components.

Board Testing

Pin mapping (revised board)

On the corrected HelloworldNew board, the button and LEDs connect to these XIAO ESP32-C3 pins:

Pin	Connected to	Direction	Notes
D7	Tactile switch (SW1)	Input	Uses INPUT_PULLUP — reads LOW when pressed
D8	LED 1 (D1)	Output	Active HIGH through 1 kΩ resistor
D9	LED 2 (D2)	Output	Active HIGH through 1 kΩ resistor

What the test program does

1. Setup: starts USB serial at 115200 baud, configures D7 as input with internal pull-up, and sets D8/D9 as outputs (both off).
2. Loop: reads the button state every 10 ms.
3. On press: when the button goes from not-pressed (HIGH) to pressed (LOW), waits 50 ms for debounce, then toggles both LEDs together.
4. Serial output: prints LED ON or LED OFF to the serial monitor so I can confirm the button is detected.

How to upload

1. Open HelloWorldWeek8.ino in Arduino IDE.
2. Board: XIAO_ESP32C3 · Port: the USB-C serial port · Enable USB CDC On Boot.
3. Upload, then open Serial Monitor at 115200 baud.
4. Press the button — both LEDs should toggle; serial monitor should print the new state.

Test firmware

Full source: HelloWorldWeek8.ino

/*
 * HelloWorldWeek8.ino
 * Button on D7 (INPUT_PULLUP) — press reads LOW
 * LEDs on D8 and D9 — toggle together on each press
 */

#define SWITCH_PIN  D7
#define LED1_PIN    D8
#define LED2_PIN    D9

bool ledState = false;
bool lastButtonState = HIGH;

void setup() {
  Serial.begin(115200);
  pinMode(SWITCH_PIN, INPUT_PULLUP);
  pinMode(LED1_PIN, OUTPUT);
  pinMode(LED2_PIN, OUTPUT);
  digitalWrite(LED1_PIN, LOW);
  digitalWrite(LED2_PIN, LOW);
}

void loop() {
  bool currentButtonState = digitalRead(SWITCH_PIN);

  // Detect falling edge: button just pressed (HIGH → LOW)
  if (lastButtonState == HIGH && currentButtonState == LOW) {
    delay(50);  // debounce
    ledState = !ledState;
    digitalWrite(LED1_PIN, ledState ? HIGH : LOW);
    digitalWrite(LED2_PIN, ledState ? HIGH : LOW);
    Serial.println(ledState ? "LED ON" : "LED OFF");
  }

  lastButtonState = currentButtonState;
  delay(10);
}

Test results

• Multimeter: no short between 5V and GND.
• USB-C connected — XIAO power LED lit up.
• Button press toggles both LEDs; serial monitor prints LED ON / LED OFF.

Result: The revised JLCPCB board passed all tests.

Hero Shot

The finished XIAO ESP32-C3 carrier board — designed in KiCad, first milled on the KEXU CNC, then revised and manufactured by JLCPCB after fixing the pull-up resistor connection.

Button press toggles the LEDs; serial monitor prints the button state over USB.

Source Files

All design, manufacturing, and firmware files for this assignment:

KiCad design

File	Description
HelloworldNew.kicad_sch	Schematic — revised design with pull-up resistor fix
HelloworldNew.kicad_pro	KiCad project file
HelloWorldWeek6-F_Cu.gbr	Front copper Gerber (original Week 6 design, used for milling)
HelloWorldWeek6-Edge_Cuts.gbr	Board outline Gerber (original Week 6 design)
Week 6 documentation	Original KiCad design workflow

Milling files (PNG → G-code)

File	Description
traces_toplayer_0.png	Trace layer image — input to Mods CE for isolation milling
outline_toplayer_2.png	Board outline image — input to Mods CE for cutout
drills_toplayer_1.png	Drill layer image
traces_toplayer_0.png.nc	Generated trace G-code — loaded on KEXU CNC to mill copper traces

Firmware (source code)

File	Description
HelloWorldWeek8.ino	Arduino test program — button on D7 toggles LEDs on D8/D9, prints state over serial

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