SpecVue

A 4-layer PCB for smart glasses featuring an ESP32-S3 with camera live streaming and on-device object classification over Wi-Fi.

Overview

This board is a compact (90×17 mm) smart glasses controller designed around the ESP32-S3. It captures video from a parallel-interface camera module, runs a lightweight object classifier (e.g., TensorFlow Lite Micro / ESP-DL) on the ESP32-S3, and streams results (bounding boxes, labels) over Wi-Fi — optionally with live video. Li-Po battery powered with built-in charging.

Block Diagram

USB-C ─┬─► MCP73831 (Charger) ──► Li-Po Battery
        │                              │
        └──► VSYS ◄────────────────────┘
               │
        ┌──────┼──────────┐
        │      │          │
   AMS1117  AP2121AK  LP2985
    3.3V      1.3V      2.8V
        │      │          │
   VDD_CPU  Core Rail  Camera IO
     & I/O    (1.3v)    (2.8v)

┌──────────────── Data Flow ────────────────┐

 Camera ──► ESP32-S3 ──┬─► TFLite Micro ──► Wi-Fi ──► Detected objects
 (DVP)      (capture)   │   (classifier)    (MQTT/UDP)
                        └─► Wi-Fi ──► Live video stream (optional)

Specifications

Parameter	Value
Board dimensions	90 mm × 17 mm
Layer count	4 (F.Cu, In1.Cu, In2.Cu, B.Cu)
Board thickness	1.6 mm
Copper weight	1 oz (0.035 mm) all layers
Dielectric	FR4 (εr = 4.5)
Input power	USB VBUS (5 V) or Li-Po battery (3.7–4.2 V)
Charger current	500 mA (set by R1 = 2 kΩ)

Power Tree

Rail	Voltage	Regulator	Max Current	Supplies
VSYS	Battery / 5V	(direct from USB-Diode-BAT path)	—	Input to all regulators
3.3 V	3.3 V	AMS1117-3.3 (U4)	800 mA	ESP32-S3 core + I/O, flash, mic
1.3 V	1.3 V	AP2121AK-1.3 (U6)	400 mA	Camera core (1.3v rail)
2.8 V	2.8 V	LP2985-2.8 (U5)	150 mA	Camera analog/digital IO (2.8v rail)

Power Path

1. USB VBUS feeds the MCP73831-2-OT (U3) Li-Po charger IC.
2. Battery connects through AO3401A (Q1) P-FET for reverse-polarity protection.
3. The FET's output (VSYS) is shared between USB and battery — no external power mux needed (Q1's body diode provides OR-ing).
4. VSYS powers all three LDOs in parallel.
5. SS14 (D4) Schottky diode provides additional input protection.

Microcontroller

ESP32-S3 (U1), QFN-56 7×7 mm, 0.4 mm pitch.

• Dual-core Xtensa LX7 @ up to 240 MHz
• Built-in Wi-Fi 802.11 b/g/n + BLE 5.0
• 512 kB SRAM, supports external PSRAM
• 40 MHz main crystal (Y2, 2520 package, 10 ppm) with 15 pF load caps
• CHIP_PU (pin 4) pulled high with a resistor, with reset button (Reset)

GPIO Allocation

GPIO(s)	Function	Connected To
GPIO4	ADC / Battery monitor	Voltage divider on VBAT
GPIO10–16, GPIO38–40, GPIO47–48	Camera parallel data bus	J4 FFC connector
GPIO17	I2C SCL	J4 pin 5 (camera control)
GPIO18	I2C SDA	J4 pin 4 (camera control)
GPIO0	Boot mode selection	Flash button
GPIO46	Strapping pin	Pull-up/pull-down resistors
U0TXD, U0RXD	Serial console	Debug UART

Note: Several GPIOs (21, 33, 37, 41–46) are available for future expansion or current sensing.

Memory

W25Q128JVS (U2) — 128 Mbit (16 MB) SPI flash, SOIC-8 package.

ESP32-S3 Pin	Flash Pin	Net
GPIO26 (SPICS0)	CS#	SPICS0
GPIO27 (SPID)	DO/IO1	SPID
GPIO28 (SPIQ)	DI/IO0	SPIQ
GPIO29 (SPIWP)	WP#/IO2	SPIWP
GPIO30 (SPIHD)	HOLD#/IO3	SPIHD
GPIO31 (SPICLK)	CLK	SPISCK

The ESP32-S3 uses its dedicated SPI2 controller for flash, with four I/O lines for Quad-SPI operation. The flash operates at 3.3 V from the VDD_CPU rail.

Camera Interface

J4 — Molex 5034802400, 24-pin 0.5 mm pitch FFC connector.

Pin	Net	Typical Camera Function
1	NC	—
2, 22	2.8 V	AVDD (analog supply)
3, 11	GND	Ground
4	IO18/SDA	SCCB / I2C data
5	IO17/SCL	SCCB / I2C clock
6	IO16	D0 (data bit 0)
7	IO15	D1
8	IO14	D2
9	IO13	D3
10	IO12	D4
12	IO11	D5
13	IO10	D6
14	IO48	XCLK (camera master clock)
15	2.8 V	DVDD (digital supply)
16	1.3 V	DOVDD (core supply)
17	IO47	D7 (data bit 7)
18	NC/Pull config	Camera ID / detection
19	IO38	VSYNC (vertical sync)
20	Pull-down (10 kΩ)	PWDN (power-down, pulled low for normal operation)
21	IO39	HREF / HSYNC (horizontal sync)
23	IO40	PCLK (pixel clock)
24	(shared pull)	Reset / detection

The pinout is compatible with OV2640/OV5640/GC2035 8-bit parallel (DVP) camera modules. The 1.3 V rail (core) and 2.8 V rails (analog + digital IO) match typical CMOS sensor requirements.

Audio

MP34DT05TR-A (U7) — MEMS digital microphone, PDM output.

Mic Pin	Net
VDD	3.3 V (from AMS1117)
GND	GND
CLK	PDM clock from ESP32-S3
DAT	PDM data to ESP32-S3
LDO	Output from internal LDO (decoupled with 0.1 µF + 10 µF)

The MP34DT05TR-A uses a 4-pin custom footprint. The PDM clock and data connect to ESP32-S3 GPIOs for audio capture alongside video streaming.

USB-C

J1 — USB-C receptacle, 14-pin (USB 2.0 only).

Feature	Implementation
CC1, CC2	5.1 kΩ pulldown (R17, R14) — sink-only, no PD
D+, D-	Series 33 Ω resistors for HS impedance matching
VBUS	Direct to charger input
SHIELD	Connected to GND via filter

No SBU lines or e-marker chip — this is a straightforward USB 2.0 sink configuration.

Battery Charger

MCP73831-2-OT (U3) — Single-cell Li-Po linear charger.

Component	Value	Purpose
R1	2 kΩ	PROG resistor — sets charge current to 500 mA
STAT	LED (D1)	Charge status indicator — on during charging, off when done, blink for fault

Status LEDs

LED	Color	Driven By	Function
D1	Red (0603)	MCP73831 STAT	Charging status — on during charging, off when done
D2	(0603)	VDD_CPU via 470 Ω	Power indicator (always on when 3.3 V present)
D3	(0603)	GPIO1 — ESP32-S3	User indicator

All LEDs have ~470 Ω series current-limiting resistors.

Antenna

AE1 — 2.4 GHz PCB antenna (TI SWRA117D reference design), left-edge placement.

This is a PCB trace antenna based on Texas Instruments application note SWRA117D. It uses an inverted-F or meandered PCB trace pattern on the board edge with a ground clearance keep-out area beneath it. The RF feed uses a pi-network (C20, C21, L6) for impedance matching. No separate antenna component is needed — the antenna is part of the PCB itself.

PCB Stackup

Layer	Material	Thickness	Type
Top solder mask	—	0.01 mm	—
F.Cu	Copper	0.035 mm	Signal + traces
Prepreg	FR4 (εr = 4.5)	0.1 mm	—
In1.Cu	Copper	0.035 mm	Signal routing
Core	FR4	1.24 mm	—
In2.Cu	Copper	0.035 mm	Signal routing
Prepreg	FR4 (εr = 4.5)	0.1 mm	—
B.Cu	Copper	0.035 mm	Signal + traces
Bottom solder mask	—	0.01 mm	—

Component Count

Category	Count
Resistors (0402)	17
Capacitors (0402)	36
Inductors	2
ICs	7
Connectors	3 (USB-C, FFC, pin header)
LEDs (0603)	3
Push buttons	2
Crystal	1
Antenna	1
Transistor (P-FET)	1
Test points	2
Schottky diode	1
Total footprints	~76

Getting Started

Prerequisites

• KiCad 9.x or later (files saved with generator v9.0)
• A 24-pin 0.5 mm pitch FFC camera module (OV2640/OV5640 compatible)

Opening the Project

git clone <repo-url>
cd SpecVue
# Open SpecVue.kicad_pro in KiCad

First-Time Setup — Footprint Libraries

Two custom footprints live in the project root as .kicad_mod files. The first time you open the project, KiCad may show warnings like "Footprint library 'FFC24' not found". This is expected — the footprint geometry is already embedded in the PCB (the board displays correctly), but the schematic-to-footprint link needs a library entry.

To resolve (one-time setup):

1. In KiCad, open Preferences → Manage Footprint Libraries (or PCB Editor → Preferences → Footprint Libraries)
2. Switch to the Project tab
3. Click Add empty row (folder+star icon) and configure each:

Nickname	Library Path	Type
FFC24	./MOLEX_5034802400.kicad_mod	KiCad
footprints	./MP34DT05TR-A_STM.kicad_mod (or use folder containing it)	KiCad

Alternatively, use a single entry pointing to the project root:

Nickname	Library Path	Type
Custom	./ (project directory)	KiCad

Then update the footprints via Tools → Update Footprints from Library and reassign FFC24: and footprints: references to the new library.

(If you skip this step, the schematic will show footprint warnings, but the PCB opens and edits fine — the geometry is stored in the .kicad_pcb file.)

Generating Gerbers

File → Fabrication → Gerbers in KiCad (no pre-built gerbers are committed).

Bill of Materials

See SpecVue.csv — all components listed with DigiKey part numbers. Key ICs:

Ref	Part	Package	DigiKey (or equivalent)
U1	ESP32-S3	QFN-56 7×7 mm	Espressif
U2	W25Q128JVS	SOIC-8	W25Q128JVS
U3	MCP73831-2-OT	SOT-23-5	MCP73831T-2ATI/OT
U4	AMS1117-3.3	SOT-223	AMS1117-3.3
U5	LP2985-2.8	SOT-23-5	LP2985-2.8DBVR
U6	AP2121AK-1.3	SOT-23-5	AP2121AK-1.3TRG1
U7	MP34DT05TR-A	Custom (MEMS mic)	MP34DT05TR-A
J1	USB-C (14-pin)	HC-TYPE-C-16P-01A	HCTL
J2	Programming header	1×02 pin header 2.54 mm	—
J4	Molex 5034802400	24-pin FFC 0.5 mm	5034802400
Y2	40 MHz crystal	2520 SMD 10 ppm	—
Q1	AO3401A	SOT-23	P-Channel MOSFET
D4	SS14	SMA	Schottky diode

Firmware Development

Use ESP-IDF or Arduino-ESP32 with the ESP32-S3 target. Key framework integration points:

• Camera: esp32-camera library (8-bit DVP mode)
• Classification: TensorFlow Lite Micro or ESP-DL for on-device inference; output is label + confidence per frame
• Communication: Stream detected objects via MQTT or UDP to a companion app/server; optionally embed bounding boxes in a live video stream
• Audio: I2S peripheral in PDM mode for the MEMS mic
• Wi-Fi: ESP32 native Wi-Fi stack for video streaming and detection telemetry

Board Dimensions

  ┌──────────────────────────────────┐
  │  90.00 mm                        │
  │                                  │
  │                                  │ 17.00 mm
  │                                  │
  └──────────────────────────────────┘

The 90×17 mm aspect fits within a standard glasses temple arm. No mounting holes — the board is intended to be secured by enclosure pressure or adhesive within the frame.

License

This hardware design is released under the CERN Open Hardware Licence Version 2 - Permissive (CERN-OHL-P-2.0).

Copyright (c) 2026 Rujul Rumale.

You may use, study, modify, manufacture, and distribute this design and products made from it; you must retain the copyright and licence notices. See LICENSE for the full text.