W-Charger

Give disposable-vape batteries a second life as low-power sensor nodes

Purpose · Hardware · Software · Upload · Security

Why W-Charger?

Disposable vapes often reach the waste stream while their small single-cell lithium batteries can still store useful energy. W-Charger gives suitable, carefully recovered cells a practical second life: they power compact ESP32-C3 nodes that measure the environment instead of becoming immediate electronic waste.

The goal is bigger than reusing one battery. This project makes a complete, understandable sensor system available—from the PCB and low-power firmware to automatic discovery, a local dashboard and optional cloud export. Connect a BME280 or BME680, place multiple nodes around a room, and turn discarded energy into useful temperature, humidity, pressure and air-quality data.

Caution

Recovering lithium cells is not a beginner task. Never use swollen, punctured, corroded, hot or deeply discharged cells. Prevent short circuits, verify polarity and voltage before connection, and take damaged cells to an approved battery recycler. W-Charger is a prototype, not a certified consumer product.

How it works

Recovered 1-cell battery
          │
          ▼
ESP32-C3 sensor board + BME280/BME680
          │  ESP-NOW
          ▼
USB-powered ESP32-S3 station
          ├── Local responsive dashboard + 24 h history
          └── Optional HTTPS upload to ThingSpeak

Part	Current implementation
Sensor node	Custom ESP32-C3 PCB V3 or V4, battery powered and mostly in deep sleep
Home station	Seeed Studio XIAO ESP32-S3, continuously powered by USB
Radio	ESP-NOW with automatic station and Wi-Fi-channel discovery
Sensors	BME280 or BME680 over I²C; operation without an environmental sensor is also possible
Configuration	Browser-based setup—no Wi-Fi password, MAC address or API key in source code
Data	Local readings and history; ThingSpeak is optional

Hardware

PCB V3 and V4

PCB V4 is the current design. Its most important change is not cosmetic: the power path now combines a buck-boost regulator with switchable sensor and battery-measurement paths. This is intended to use more of the cell's discharge range and reduce avoidable deep-sleep losses.

PCB V3 · previous design	PCB V4 · current design
Front	Front
Back	Back

Focus	PCB V3	PCB V4
3.3 V supply	DS8561-33S5 LDO	TPS63900 buck-boost regulator
Usable battery range	Limited by LDO headroom	Designed to maintain 3.3 V across more of the Li-ion discharge curve
Sensor rail	GPIO10, active-high switching	PMOS power gate on GPIO10, active-low; sensor and I²C pull-ups are off during sleep
Battery measurement	ADC on GPIO3; divider remains connected	ADC on GPIO3 plus GPIO6 enable; divider is powered only for a reading
Battery connector	Earlier vertical connector layout	Low-profile, side-entry two-pin SMD connector
Charging/status	TC4056A-based layout	Revised TP4056 thermal-pad layout with clearer power/charge indicators
Firmware target	sensor_pcb_v3	sensor_pcb_v4
Status	Existing prototype	Current prototype; complete electrical, thermal, RF and runtime validation is still required

Both revisions expose the same four-pin I²C interface: 3V3 · SDA (GPIO5) · SCL (GPIO4) · GND. The shared sensor firmware selects the correct pin polarity and battery-measurement behavior through its build profile.

The KiCad sources, BOM and production files are in PCB/. For V4, the manufacturing package is under PCB/Version 4/ESP32-C3-V4/production/.

Software

There is one maintained firmware implementation under Firmware/:

Module	Role
station/	ESP32-S3 setup portal, local dashboard, sensor registry, history and optional ThingSpeak integration
sensor/	One ESP32-C3 codebase for PCB V3/V4 and BME280/BME680
shared/	Versioned ESP-NOW protocol shared by station and sensor

Old experiments are intentionally excluded from Git. The Firmware/ directory is the single source of truth.

Station dashboard

The station opens a browser-based setup flow on first boot. Afterwards the overview shows connection state, discovered sensors, latest readings, battery voltage, radio strength, ThingSpeak status and a local rolling 24-hour history.

_{Station overview with anonymized demo identifiers.}

Each sensor can be named and configured independently. Measurements can be mapped to ThingSpeak fields 1–8 or kept local. BME680 nodes also show Static IAQ, BSEC accuracy and gas resistance.

_{Multiple sensor cards, local history and optional cloud field mapping. All device and channel identifiers are demo values.}

Key behavior:

• New sensors discover the station automatically across all 13 ESP-NOW channels; no receiver MAC or channel is compiled into the sensor.
• BME280 nodes wake only for their configured measurement interval.
• BME680 nodes use Bosch BSEC2 in ULP mode. Internal measurements run every five minutes while radio reports follow the configured longer interval.
• Initial BME680 stabilization takes roughly 20 minutes; background learning continues afterwards.
• The station retains a rolling 24-hour history for every sensor. Its local history step follows that sensor's measurement interval, so a 10-minute interval produces 10-minute points and a 20-minute interval produces 20-minute points.
• ThingSpeak channels and field mappings are optional and configured centrally in the station UI. Initial setup only asks for the account User API Key; channel creation, selection, keys and field mapping remain in the dashboard.

Upload the firmware

What you need

• VS Code with the PlatformIO IDE extension, or standalone PlatformIO Core
• Git and Python
• A USB data cable
• One connected board at a time

For the first USB upload, disconnect the recovered battery and power the board from USB. Confirm the sensor PCB revision before flashing: V3 and V4 use different power-control logic.

Simplest method

Clone or download this repository, open a terminal in its root directory, then run:

python Firmware/upload.py

Choose the connected station, V3 sensor or V4 sensor from the menu. The helper finds a standard PlatformIO installation and runs the correct project and build environment.

For a direct, repeatable command:

python Firmware/upload.py station
python Firmware/upload.py sensor-v4
# For an existing V3 board:
python Firmware/upload.py sensor-v3

On Windows, py can be used instead of python; on macOS or Linux the command may be python3. If multiple serial devices are connected, add --port COM5 or the matching /dev/... device.

Important

Every station upload performs a full flash erase by design. Saved Wi-Fi settings, website password, ThingSpeak keys, sensors and local history are removed. Sensor firmware updates also start a fresh pairing state for a new firmware image.

Upload with the PlatformIO button instead

1. Open Firmware/station as a PlatformIO project.
2. Connect the ESP32-S3 station and select PlatformIO: Upload.
3. Open Firmware/sensor as a PlatformIO project.
4. Select sensor_pcb_v3 or sensor_pcb_v4 in the PlatformIO environment selector, connect the matching ESP32-C3 board and choose Upload.

If no upload port is found

• Confirm that the cable supports data, not charging only.
• Disconnect other ESP boards or pass --port explicitly.
• Put the board into download mode: hold BOOT, tap RESET (or reconnect USB), then release BOOT when the upload begins.
• On Windows, a short clone path can avoid toolchain problems when long-path support is disabled.

All three release targets currently compile successfully: station_s3, sensor_pcb_v3 and sensor_pcb_v4.

First start

1. Flash the station.
2. Join W-Charger-XXXXXX with the initial setup password W-Charger-Setup. This is a public bootstrap password, not a personal credential.
3. If the captive portal does not open, browse to http://192.168.4.1/. Select a 2.4 GHz home network, optionally enter the single ThingSpeak User API Key and set the recommended website password. Advanced ThingSpeak channel settings are available later in the dashboard.
4. After the station joins the home network, open http://w-charger.local/ or the LAN address shown during setup.
5. Flash and power the matching sensor board. Open Find sensors, name the detected node, select BME280/BME680 (or automatic detection), choose its interval and save.

No serial monitor and no source-code credential file are required. Firmware updates are currently USB-only; OTA update slots are reserved but the OTA flow is not implemented.

Security and privacy

This repository is designed to be public:

• Wi-Fi passwords, website credentials and ThingSpeak API keys are never compiled into the firmware. They are entered in the station UI and stored in ESP32 NVS.

• Documentation screenshots use anonymized MAC addresses, local IPs, entry numbers and ThingSpeak channel IDs.

• Local credential files, build output, compiler databases, private keys, machine-local KiCad exports and the retired firmware tree are ignored.

• Optional Git hooks block common credential files and likely secrets before a commit or push:

  git config core.hooksPath .githooks

Set a station website password before using ThingSpeak. Without it, another device on the same trusted LAN could view configuration and API keys. When enabled, the station uses independent, bounded in-memory login sessions with a 30-minute absolute lifetime, CSRF-protected server-side sign-out, device-wide login throttling, CSRF and same-origin checks, and compact browser security headers. These protections are intentionally lightweight for the ESP32-S3.

The local dashboard still uses HTTP, so its password protects access but does not encrypt local traffic. Publicly trusted certificates cannot cover the station's .local name or changing private IP address, while a self-signed certificate would require a browser exception and would interfere with the captive-portal flow. Use the dashboard on a trusted home network. ThingSpeak requests use HTTPS.

ESP-NOW packets currently have protocol versioning, length checks and CRC32, but no per-device cryptographic authentication. Treat the current system as a trusted-home-network prototype.

Repository structure

.
├── Firmware/
│   ├── station/        # ESP32-S3 station
│   ├── sensor/         # ESP32-C3 sensor, PCB V3 and V4
│   └── shared/         # Common ESP-NOW protocol
├── PCB/
│   ├── Version 1–3/    # Earlier hardware revisions
│   └── Version 4/      # Current KiCad and production files
├── Readme/             # Public documentation images
├── .githooks/          # Optional secret guards
├── .gitignore
├── LICENSE
└── README.md

Detailed references:

• Firmware overview
• Station behavior and security model
• Sensor behavior, BME680 and hardware profiles
• System architecture
• Hardware test plan

License

Project-owned source and hardware files are released under the MIT License. The optional BME680 path downloads Bosch BSEC2 during the build; that dependency is distributed under Bosch's separate BSEC license.