Week 9: On Painting with Output Devices

This week I added an audio output path to my custom XIAO ESP32-S3 board: a tiny class-D amplifier driving an 8 Ω speaker. The focus was on hardware design—schematic edits, routing, power integrity, and fabrication—so I can program it next.

Week 9 system: audio amp + speaker + circular board.

Assignment

Add an output device to a microcontroller board you designed, and program it to do something.

I implemented the hardware path first (MCU → amplifier → speaker). Firmware comes next.

Starting Point: Week 6 Board

I reused the circular ESP32-S3 board from Week 6. It already had: stable power, XIAO footprint, and generous routing space.

Circular PCB test layout — The baseline board layout inherited from Week 6.

Choosing the Amplifier & Speaker

Amplifier: tiny class-D breakout (VIN, GND, IN, OUT+, OUT−).
Speaker: 8 Ω mini speaker.
Audio Source: ESP32 PWM/DAC pin.

Board shape for amplifier and speaker pads — Early layout where I made room for the amp and speaker pads.

Schematic Changes

Added an amplifier symbol (IN, VIN, GND, OUT+, OUT−).
Connected an ESP32 PWM/DAC pin → IN.
Added 1 µF and 0.1 µF decoupling capacitors near VIN.
Added large THT pads for the speaker wires.

KiCad routing view — Tracing the audio path from the XIAO to the amplifier input.

Footprints & Mechanics

Two 1×7 headers spaced exactly 17.78 mm for the XIAO.
Converted SMD headers → true **THT** so drills would generate.
Used large pads for speaker wires with mechanical relief.
Clean single outline on Edge.Cuts.

Footprint alignment screenshot — Header geometry and footprint alignment check.

Routing & Power Integrity

Default track width: 0.4 mm; power rails: 0.7–0.8 mm.
Large ground plane on F.Cu and B.Cu, tied to GND.
Short, clean trace for amp input.
Decoupling capacitors placed tight to VIN.

Traces top layer rendering — Final top-layer routing: audio trace short and isolated.

Speaker Integration

The class-D amplifier outputs a differential pair. I routed SPK+ and SPK− to large through-hole pads and left room for strain-relief heatshrink.

Speaker routing area — Speaker pad area with stout traces from OUT+ / OUT−.

Fabrication Files

The final board was exported as Gerbers and drills for manufacturing.

Gerber outline view — Gerber outline preview used for milling.

Assembly & Bring-Up

Soldered headers & amplifier.
Attached speaker wires with strain-relief.
Continuity-tested all nets.
Powered via USB and verified amplifier current draw.

Debugging Notes

Empty drill files? Caused by SMD headers → fixed by switching to THT.
No ground plane? Must assign zone to net GND.
Noise risk: Keep amp input short; decouple VIN aggressively.

Next Steps

Generate a tone via PWM or DAC.
Map Week 8 capacitive pads → play/pause/volume.
Check SNR, hiss, grounding.