Bikesensor pcb

bikesensor 🚲📡

A standalone, low-cost, pure IoT hardware and software mapping pipeline for geo-tagged bike vibration and road-quality analysis.

bikesensor turns an ESP32-C3 SuperMini, an MPU-6050 IMU, a NEO-6M GPS, and an SPI MicroSD card module into a standalone, battery-powered mapping box.

When you ride, the device autonomously records high-frequency (200 Hz) vertical accelerometer vibrations and sparse (1 Hz) GPS coordinate ticks into unified local CSV log files on the SD card. When you return home, the device connects to your home Wi-Fi and uploads all offline ride CSVs over HTTPS to kiel.earth, where the rides are stored, processed and mapped. That website lives in its own repository; this one holds the firmware, the carrier PCB and the enclosure.

⚠️ Project status

• The custom PCB has been ordered (38.74 × 114.47 mm, production/bikesensor.zip) but not assembled. Its ESP32 headers were routed against the wrong SuperMini pinout, so every signal lands on a different GPIO than the hand-wired prototype used. The default firmware build is remapped to match the board; the battery sense needs one bodge wire during assembly, and the module must be mounted face down. Details in custom_pcb/PIN_VERIFICATION.md.
• The hardware has never produced a real ride. Every figure produced so far comes from synthetic signals.

📸 Hardware Showcase

Below is the completed physical system mounted on a custom 3D-printed handlebar enclosure and its 3D modeling design:

Physical System	3D Printed Enclosure Design

1. System Architecture

flowchart TD
    subgraph Riding [1. Outdoor Bike Ride]
        ESP[ESP32-C3 SuperMini]
        IMU[MPU-6050 Accelerometer 200Hz] --> ESP
        GPS[NEO-6M GPS Module 1Hz] --> ESP
        ESP -->|Log unified CSV| SD[(SPI MicroSD Card)]
    end

    subgraph Home [2. Arrival Home & Wi-Fi Sync]
        ESP_H[ESP32-C3 Home Mode] -->|Connects to home Wi-Fi| Router((Home Router))
        SD -->|Stream CSVs over HTTPS POST| ESP_H
        ESP_H -->|/api/bike/ingest| Site[kiel.earth]
        Site -->|2xx: file is stored| ESP_H
        ESP_H -->|Delete uploaded file| SD
    end

2. Hardware Wiring & Custom PCB Carrier

The hardware operates on 3.3V logic for standard communication and SD logging, driven by a Wemos D1 Mini TP5400 Battery Shield.

Here is the physical wiring diagram for our custom carrier board:

Schematic

R3 (10 kΩ) pulls SPI_CS to +3V3, keeping the card deselected while the ESP32 boots. The schematic's ESP32 connectors are generic sockets, so it does not show which GPIO each net reaches; the table below does.

Board

The carrier is 38.74 × 114.47 mm, 2-layer, all through-hole. Every connected pin carries a silkscreen signal name — GTX/GRX are the GPS UART, DTX/DRX the debug UART, and ADC the battery divider.

Pin Map Table:

GPIOs are for the carrier PCB (default firmware build). The hand-wired prototype used different ones — pio run -d firmware -e handwired.

3. Firmwares (PlatformIO)

The firmware resides in firmware/bikesensor/bikesensor.ino and compiles out-of-the-box.

Secure Credentials (Git-Ignored)

To protect your home Wi-Fi passwords from being committed to Git, create a file named private_credentials.h inside firmware/bikesensor/:

#pragma once
#define WIFI_SSID "YourHomeSSID"
#define WIFI_PASS "YourHomePassword"
#define SERVER_HOST "kiel.earth"
#define SERVER_PORT 443
#define SERVER_UPLOAD_PATH "/api/bike/ingest"
#define DEVICE_TOKEN "your-device-token"   // sent as: Authorization: Bearer <token>

The firmware preprocessor will automatically detect and include this file during compile, keeping your passwords safe and isolated in your local workspace.

Compilation Commands:

pio run -d firmware              # Build firmware binary
pio run -d firmware -t upload    # Flash to ESP32-C3 (Serial port is auto-detected)
pio device monitor -b 115200     # Real-time console debugger

4. Device-to-Server Interface

The logging box talks to the website over a single HTTPS endpoint.

4.1 CSV Log Data Format

When writing to the MicroSD card, the device registers data in a unified, comma-separated format:

millis,ax,ay,az,lat,lon,ele,speed_kmh,battery_pct,gps_time

• millis: Relative milliseconds from ESP32 boot (used to align high-frequency vibration data).
• ax,ay,az: Raw vertical/lateral/longitudinal accelerometer values (the ±4 g scale, 1/8192, is applied on the website, not on the device).
• lat,lon,ele,speed_kmh: GPS coordinate details.
• battery_pct: Divided battery measurement (0 - 100%) read from GPIO 3 on the carrier PCB (GPIO 0 on the hand-wired prototype).
• gps_time: GPS UTC timestamp (used as a clock reference).

4.2 Wireless Sync Protocol

When the ESP32-C3 boots in Wi-Fi sync mode upon returning home, it uploads every ride file on the SD card, one HTTPS request each:

• HTTP Method: POST
• Request URL: https://kiel.earth/api/bike/ingest (set by SERVER_HOST / SERVER_UPLOAD_PATH)
• Request Headers: Content-Type: text/csv, Authorization: Bearer <DEVICE_TOKEN>, X-Ride-Id: <filename without .csv>
• Request Body: the raw CSV file.

The device deletes a file from the SD card only after a 2xx response. On a timeout, TLS failure or any other status it keeps the file and retries on the next sync.