Wireless switch

Wireless Race Car Switch System — Hardware v2 (WiFi)

A fully wireless switch panel for a race car using two Raspberry Pi Pico 2 W boards.
One board acts as the Transmitter (switch panel), the other as the Receiver (12 V output driver).

Bluetooth version: see the bluetooth branch.

System Overview

 ┌──────────────────────────┐      WiFi (AP/STA)      ┌─────────────────────────────┐
 │      TRANSMITTER         │ ◄──── UDP 20 Hz ──────► │        RECEIVER             │
 │    Raspberry Pi Pico 2W  │                          │    Raspberry Pi Pico 2W     │
 │                          │  Web UI: 192.168.4.1     │  Web UI: <RX-IP>            │
 │  GPIO 1-5 ← 5 switches   │                          │  GPIO 8-11 → 4× MOSFET     │
 │  GPIO 0  → Connected LED │                          │  GPIO 12   → Relay K2      │
 │  GPIO 7  → Searching LED │                          │  GPIO 0    → Connected LED  │
 │  Powered from 12 V via   │                          │  GPIO 7    → Searching LED  │
 │  on-board 5 V regulator  │                          │  Takes 12 V from car        │
 └──────────────────────────┘                          └─────────────────────────────┘

TX creates an open WiFi access point (WirelessSwitch-1 by default). RX connects as a station.
Both boards host a web settings page — join the WiFi network and open a browser to configure.

Web Interface

Connect any phone or laptop to the WirelessSwitch-N WiFi network (no password), then open the URL above. Settings are saved to flash and survive power cycles.

GPIO Pin Mapping — Hardware v2

Status LEDs (identical on both boards)

Transmitter — Switch Inputs

Switches are active-low (connect switch between GPIO pin and GND).
Internal pull-ups enabled in firmware.

Receiver — Output Channels

Outputs are active-high (GPIO HIGH = output energised).

Repository Structure

├── kicad/
│   ├── wireless_switch.kicad_pro   KiCad project file
│   ├── wireless_switch.kicad_sch   Top-level schematic
│   ├── Pico_interface.kicad_sch    Pico 2 W GPIO interface sub-sheet
│   ├── analog_in.kicad_sch         Output channel sub-sheet (MOSFET + relay)
│   ├── input_power.kicad_sch       12 V → 5 V power supply sub-sheet
│   ├── wireless_switch.kicad_pcb   PCB layout
│   └── sym-lib-table               KiCad symbol library table
│
├── firmware/
│   ├── config.py        Shared configuration (defaults – overridden by web UI)
│   ├── tx_main.py       Transmitter MicroPython firmware
│   ├── rx_main.py       Receiver MicroPython firmware
│   ├── install_tx.bat   Windows transmitter installer  (default COM3)
│   ├── install_rx.bat   Windows receiver installer     (default COM5)
│   ├── install_tx.sh    Linux / macOS transmitter installer
│   ├── install_rx.sh    Linux / macOS receiver installer
│   ├── verify.bat       18-point verification script (Windows)
│   ├── led_test.bat     LED blink test (Windows)
│   └── polarity_test.bat  LED polarity / GPIO finder (Windows)
│
└── docs/
    └── wireless_switch.pdf   Full schematic PDF

Hardware Requirements

Per Board (× 2)

• Raspberry Pi Pico 2 W
• PCB from kicad/wireless_switch.kicad_pcb

Transmitter PCB BOM additions

• 5× panel-mount toggle switches (SPDT or SPST)
• 2× LEDs with 330 Ω series resistors for GPIO 0 & 7
• 12 V → 5 V onboard regulator + capacitors (see input_power.kicad_sch)

Receiver PCB BOM additions

• 4× N-channel logic-level MOSFETs (e.g. IRLZ44N) with gate resistors
• 1× 12 V SPDT relay K2 (Omron G5V-1 or equivalent)
• Relay driver transistor + flyback diodes
• Fusing on each output channel

Software Installation

Step 1 — Flash MicroPython to each Pico 2 W

1. Download the Pico 2 W MicroPython UF2 from
   https://micropython.org/download/RPI_PICO2_W/
2. Hold BOOTSEL, plug USB → Pico appears as RPI-RP2 mass storage
3. Drag the .uf2 onto the drive — Pico reboots automatically

Step 2 — Install mpremote

pip install mpremote

Step 3 — Install Transmitter firmware

Windows (default COM3):

cd firmware
install_tx.bat
install_tx.bat COM4    ← specify a different port if needed

Linux / macOS:

cd firmware
chmod +x install_tx.sh && ./install_tx.sh

Confirm: board blinks SEARCHING LED 3× quickly then flashes slowly.

Step 4 — Install Receiver firmware

Windows (default COM5):

install_rx.bat

Linux / macOS:

./install_rx.sh

Step 5 — Verify (optional, Windows)

verify.bat COM3 COM5
led_test.bat COM3 COM5

Operation

1. Power on both boards. Both blink the SEARCHING LED 3× quickly to confirm firmware is running.
2. TX creates an open WiFi access point. Both boards flash their SEARCHING LED while waiting for a link.
3. Once linked, CONNECTED LED turns solid on both boards; SEARCHING LED turns off.
4. Pressing a switch on TX activates the corresponding output on RX according to that channel's mode.
5. On link loss: RX holds its last output states for the configured hold time (default 10 s), then turns all outputs off. Both boards resume searching.

Link Parameters

Channel Modes

Each output channel can be set independently via the RX web interface:

Latch state is preserved through brief disconnects (within hold window).
A disconnection longer than the hold time resets all latch states to OFF.

Multiple Pairs

If two TX/RX pairs operate at the same time, each pair needs a unique Pair ID so they don't cross-connect.

Set the same Pair ID on both boards in a pair via the web interface:

Procedure for changing Pair ID:

1. Connect to the current WiFi network
2. Open RX settings → change Pair ID → Save (RX reboots, now looks for new SSID)
3. Open TX settings (192.168.4.1) → change Pair ID → Save (TX reboots with new SSID)
4. RX reconnects automatically

Troubleshooting

Protocol Reference

UDP packet format (7 bytes, TX → RX, port 4210):

Byte 0   : 0xAA  (start marker)
Byte 1   : Switch 1 state  (0 = open, 1 = pressed)
Byte 2   : Switch 2 state
Byte 3   : Switch 3 state
Byte 4   : Switch 4 state
Byte 5   : Switch 5 state
Byte 6   : Checksum  = (SW1+SW2+SW3+SW4+SW5) & 0xFF

RX → TX heartbeat: b"RXHERE" (6 bytes, every 50 ms) — tells TX the RX's IP address.