Opentouch s3

OpenTouch S3

Rev B1 · an open hardware remake of the Bare Conductive Touch Board

Project page · Schematic · Fab files · Order it

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A modern remake of the Bare Conductive Touch Board: 12 capacitive touch electrodes, MP3/WAV/MIDI audio, and now WiFi, Bluetooth LE, USB-C, a proper LiPo power path, a fuel gauge, line-in, MIDI out, Qwiic and an RGB LED.

Based on the Bare Conductive Touch Board open hardware files (CC BY-SA 3.0, https://github.com/BareConductive/touch_board_cad_files). This is an independent adaptation, not affiliated with or endorsed by Bare Conductive, and released under the same licence (CC BY-SA 3.0).

Status: Rev B1, design complete, not yet fabricated or tested. Read "Before you order" below.

What's in this repository

Project page

To publish the project page: repo Settings > Pages > Source: Deploy from a branch > Branch: main, folder /docs > Save. It will appear at https://<your-username>.github.io/opentouch-s3/.

Board summary

• 100 x 90 mm, 4 layers (signal / GND plane / 3V3 plane / signal), 1.6 mm, ENIG recommended (the electrode pads are exposed)
• MCU: ESP32-S3-WROOM-1-N16R8 (16 MB flash, 8 MB PSRAM), native USB (CDC + MIDI capable), WiFi, Bluetooth LE. The module is pre-certified for radio (FCC / CE-RED / UKCA), so the board needs no intentional-radiator certification of its own.
• Touch: NXP MPR121 at I2C 0x5C (same address as the Touch Board), 12 electrodes on crocodile-clip pads, 3.5 mm screw terminals and a 2.54 mm header. Every electrode has ESD protection (SRV05-4).
• Audio: VS1053B. Headphone out (AC coupled, safe into any amplifier), stereo line-in (record to SD), microSD, real-time MIDI synth mode.
• Power: USB-C sink (5.1 k CC resistors, works with C-to-C cables), BQ24074 power-path charger (input OVP to 10.5 V, 1 A input limit, 500 mA charge, cut JP1 for 250 mA), JST-PH LiPo input with reverse polarity MOSFET and PTC fuse, TPS63001 buck-boost 3.3 V (runs the board across the whole LiPo range), MAX17048 fuel gauge (I2C 0x36). The power switch turns the board off while charging continues. External 4.5-10 V input on the VIN header pin.
• I/O: Arduino R3 header pattern (3.3 V logic, do not feed 5 V into IO pins), Qwiic / STEMMA QT, MIDI OUT on a 3.5 mm TRS type A jack (tip = MIDI pin 5, ring = pin 4, MMA CA-033 3.3 V signalling), WS2812B-2020 RGB LED, BOOT and RESET buttons, test points on every rail.

ESP32-S3 pin map

Strapping pins are handled: IO0 has the BOOT button, IO45 drives an LED to ground (low at boot), IO46 holds the VS1053 in reset through a 100 k pull-down (low at boot), IO3 is only used as a plain digital pin.

Solder jumpers

Ordering at JLCPCB

1. Upload OpenTouch_S3_gerbers_JLCPCB.zip. Choose 4 layers, 1.6 mm, ENIG surface finish (for the touch pads), any mask colour.
2. Enable PCB Assembly, top side. Upload the BOM and CPL files.
3. Check the part placement preview. Rotations were corrected for JLCPCB's conventions, but always confirm pin 1 on the ICs (U2, U3, U4, U5, U6, U10) and the connectors before confirming.
4. The Arduino headers (J13-J16), the touch header (J9) and the NTC header (J2) are left unfitted on purpose. Solder them yourself if you want them.
5. Stock note: the 12.288 MHz crystal (Y1, NX3225GA) has low stock at LCSC. Any 3.2 x 2.5 mm 12.288 MHz crystal with 8 pF load works (e.g. ABM8-12.288MHZ-8-D1X-T). With a different load capacitance change C18/C19 to 2 x (CL - 3 pF).

First power-up

1. Before connecting anything, measure resistance from 3V3 (TP2) and VSYS (TP1) to GND (TP4). Both should read well above 100 ohms.
2. Plug in USB-C with the switch ON: the green PWR LED lights, TP2 reads 3.3 V, TP1 about 4.4 V. With a battery attached the yellow CHG LED shows charging.
3. The ESP32-S3 appears as a USB serial device. If it doesn't, hold BOOT, tap RESET, release BOOT.

Before you order

• Open it in KiCad and review the layout. The board was placed by script and routed with Freerouting plus scripted repairs. KiCad's DRC reports 0 unconnected pads and 0 clearance, hole or edge errors, and the PCB, schematic and design.py netlist agree on all 609 pads. Some routes are longer than a hand layout would be, so it is worth a look, especially the 3.3 V buck-boost loop (U4, L1, C8-C10) and the USB D+/D- pair.
• Remaining DRC warnings are cosmetic: silkscreen touching silkscreen or pads (pads are cleared automatically in the Gerbers), edge-connector outlines crossing the board edge, and courtyard overlaps between the interlocking screw terminals.
• Input current limit is about 1 A. From a laptop USB-A port (500 mA) with WiFi busy and a battery charging, the port may current-limit. Use a USB-C charger, or cut JP1 to halve the charge current.
• The 5V header pin is USB VBUS. Don't power the board through it; use VIN (4.5-10 V) instead.
• Confirm which slide-switch position is ON with the green PWR LED; the silkscreen only says POWER.

Software

Arduino IDE with the Espressif ESP32 core (board: "ESP32S3 Dev Module", USB CDC On Boot enabled, PSRAM "OPI PSRAM", flash 16 MB). Libraries that work with this pin map:

• Touch: Bare Conductive MPR121 library or Adafruit_MPR121 (address 0x5C, IRQ on IO10).
• Audio: Adafruit_VS1053 with Adafruit_VS1053_FilePlayer player(46, 15, 16, 17, 14); (reset, CS, DCS, DREQ, card CS). Call SPI.begin(12, 13, 11) first so the ESP32 uses this board's SPI pins.
• Fuel gauge: SparkFun MAX1704x or Adafruit_MAX1704X.
• RGB LED: Adafruit_NeoPixel or FastLED on IO48.
• MIDI out: Arduino MIDI library on Serial1 with TX mapped to IO47 (31250 baud).
• USB MIDI: the ESP32-S3 USB stack (TinyUSB) can present the board as a class-compliant USB MIDI device.

Touch Board sketches port mostly by changing pin numbers: the MPR121 address and electrode numbering are unchanged.

Regenerating the design

hardware/gen/design.py is the single source of truth (every part, value, LCSC number and pin-to-net mapping). make_sch.py writes the schematic, make_pcb.py places the board, pipeline.sh runs autorouting and repairs, export_fab.py writes the JLCPCB files. The scripts need KiCad 7's Python module, Java and Freerouting 1.9, and use absolute paths from the machine they were written on, so adjust the paths at the top of each script first.

Licence

CC BY-SA 3.0, the same licence as the original Touch Board design. See LICENSE.md and NOTICE.md.