Breadboard Prototype

I started by testing the circuit on a breadboard with the XIAO RP2040, three LEDs (yellow, green, and red), each with a current-limiting resistor, and a tactile push button. Pressing the button lights the LEDs, which confirmed the wiring and pin assignments before I moved into KiCad.

Schematic (KiCad)

In the KiCad Schematic Editor, I placed the XIAO RP2040 module (M1) and extended the circuit to five LEDs (D1–D5). Each LED connects to its own pin, D6 to D10, through a 1 kΩ resistor (R1–R5), and all the cathodes return to GND. The push button (SW2) connects D1 to GND, so the pin reads low when pressed. I added a PWR_FLAG to the ground net so the electrical rules check knows it is driven, and marked the unused pins with no-connect flags.

PCB Layout (KiCad)

I then updated the PCB from the schematic and arranged the footprints in the PCB Editor, placing the resistor and LED pairs in a row below the XIAO and routing each signal to its pin, then checked the result in the KiCad 3D Viewer.

Breadboard Prototype

To make the bot modules move on their own, I prototyped a circuit that drives two micro servo motors from a Seeed Studio XIAO ESP32-S3. The servos take power from the 5V pin and their PWM signals from two GPIO pins. A push button triggers the motion and an LED shows the state. I chose the ESP32-S3 because its built-in Wi-Fi and Bluetooth will later let the modules communicate wirelessly.

Schematic (KiCad)

I redrew the prototype as a schematic in KiCad. For the microcontroller (M1), I used the XIAO RP2040 symbol and footprint from the library, because the XIAO ESP32-S3 has the same size and the same pin positions for D0–D10, 5V, and GND, so the board fits either module. D1 and D2 send PWM signals to the two servos (M2 and M3). D3 reads the push button (SW1), which connects to GND, and D0 drives the status LED (D1) through a 1 kΩ resistor (R1). I added a 10 µF capacitor (C1) between 5V and GND to smooth the current spikes from the servos when they start moving, and PWR_FLAGs on the 5V and GND nets to pass the electrical rules check.

In the first version, the extra resistor R2 was wired incorrectly. I changed it to a 0 Ω resistor that links the servo ground to the main ground. On a single-sided board it works as a jumper, so the ground connection can cross over the signal traces without a via.

Design Rules (KiCad)

Before routing, I set the board constraints to suit milling: 0.4 mm minimum clearance, 0.4 mm minimum track width, and 0.5 mm copper-to-edge clearance. I also created a Power net class with 1 mm tracks and assigned the +5V and GND nets to it, so the servo current runs on wider traces, while the signal nets keep the 0.4 mm default.

PCB Layout (KiCad)

In the PCB Editor, I placed the XIAO at the top with the LED, resistor, and button on the left and the two servo headers at the bottom edge so the cables can leave the board cleanly. I routed every connection on the front copper layer (F.Cu) only, with no vias, and used the Net Inspector to check each net's track length. The board ended up with 52 pads, 59 track segments, and no unrouted connections.

I also checked the front solder mask layer (F.Mask) to confirm that the pads were exposed for soldering.

Board Outline and Ground Fill

Finally, I drew the board outline on the Edge.Cuts layer as a 37.5 mm × 41.5 mm rectangle and filled the free copper area with a ground zone. The ground fill reduces the amount of copper to mill away and gives the servos a solid return path.

3D View (KiCad)

I checked the finished board in the KiCad 3D Viewer to confirm the component placement, traces, and ground fill.