"A Raspberry Pi 4 drawing 4W to read one MPPT is an absurd tax on a solar battery."
ESP32 firmware that reads a Victron SmartSolar MPPT over Bluetooth LE, decrypts the advertisement, and publishes it to MQTT with full Home Assistant auto-discovery — at ~0.15W instead of ~4W.
Victron's victron-ble Python library is excellent, and running it on a Raspberry Pi 4 works
perfectly — until you notice the Pi is idling at 3–5W purely to relay a few numbers off a
charge controller. On an off-grid system that's around 40Wh a night, or 3–4Ah at 12V:
the monitoring was costing more than the thing it was monitoring.
This firmware does the same job on an ESP32 at roughly a fortieth of the power, and behaves better in Home Assistant while it's there.
| 📶 Reads the advertisement | Passive BLE scan of the SmartSolar MPPT's broadcasts — no pairing, no connection, lower draw. |
| 🔐 Real decryption | AES-128-CTR exactly as the Victron BLE protocol specifies, matching the reference Python implementation bit for bit. |
| 📡 MQTT every 10s | One JSON payload with every value, plus a retained online/offline LWT topic. |
| 🏠 Auto-discovery | Appears in Home Assistant as a Victron SmartSolar MPPT device with entities grouped. No YAML. |
| 🧵 Two cores, no crashes | BLE scanning pinned to core 1, WiFi/MQTT to core 0 via FreeRTOS — sidesteps the radio coexistence crashes that come from sharing a core. |
| 🔌 External load too | The MPPT's load output current is published as amps, and multiplied by battery voltage to give watts — so the dashboard shows draw as well as charge. |
| 📊 Dashboard included | A ready-made Mushroom + Mini Graph dashboard card and optional template sensors. |
| 🪫 0.15W idle | The entire point. |
flowchart LR
mppt["☀️ Victron SmartSolar MPPT<br/><i>BLE advertisement, encrypted</i>"]
subgraph esp["⚡ ESP32 · dual core"]
core1["Core 1 · NimBLE<br/><i>passive scan</i>"]
dec["victron_ble.cpp<br/><i>AES-128-CTR + bit unpack</i>"]
core0["Core 0 · WiFi + MQTT<br/><i>PubSubClient</i>"]
core1 --> dec --> core0
end
broker["Mosquitto<br/><i>solar/mppt/#</i>"]
ha["Home Assistant<br/><i>auto-discovered</i>"]
mppt -.->|"~every few seconds"| core1
core0 -->|"every 10s"| broker --> ha
style core1 fill:#e7352c,stroke:#e7352c,color:#fff
style dec fill:#6f42c1,stroke:#6f42c1,color:#fff
style core0 fill:#334155,stroke:#334155,color:#fff
style broker fill:#660066,stroke:#660066,color:#fff
style ha fill:#41bdf5,stroke:#41bdf5,color:#fff
SmartSolar MPPTs broadcast encrypted BLE advertisements every few seconds. Decryption uses AES-128-CTR with your device's 32-character hex key, and a 16-bit nonce from the advertisement used as the little-endian initial value of a 128-bit counter. The plaintext is a bit-packed structure read LSB-first.
- An ESP32 dev board — tested on the ESP32 CH340 38-pin
- Within BLE range of the SmartSolar MPPT (~10m)
- A WiFi network
The ESP32-C3 SuperMini also works, but needs the BOOT button held during flashing. The classic CH340 board is the easier one to live with.
git clone https://github.com/MrSossidge/victron-esp32-ble-mqtt.git
cd victron-esp32-ble-mqttInstall VS Code and the PlatformIO IDE extension, then
open the project folder — PlatformIO reads platformio.ini and pulls dependencies itself.
cp include/example.config.h include/config.h#define WIFI_SSID "your_wifi_ssid"
#define WIFI_PASSWORD "your_wifi_password"
#define MQTT_HOST "192.168.1.x" // your MQTT broker IP
#define VICTRON_MAC "xx:xx:xx:xx:xx:xx" // lowercase, colon-separated
#define VICTRON_ENC_KEY "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" // 32 hex charsconfig.h is gitignored — your key does not end up in a commit.
Finding your MAC address and encryption key
- Open the Victron Connect app
- Connect to your SmartSolar MPPT
- Tap the ⋮ menu → Product Info
- The MAC address is at the top of that page
- Scroll to Instant readout via Bluetooth and tap SHOW for the encryption key
| Action | Shortcut |
|---|---|
| Build | Ctrl+Alt+B |
| Upload | Ctrl+Alt+U |
| Serial monitor | Ctrl+Alt+S |
| Topic | Description |
|---|---|
solar/mppt/data |
JSON payload with all sensor values |
solar/mppt/status |
online / offline (retained LWT) |
{
"battery_voltage": "12.98",
"battery_current": "-0.20",
"pv_power": "8.0",
"yield_today_wh": "350",
"charge_state": "bulk",
"charge_state_raw": 3,
"error_code": 0,
"external_load_a": "0.35",
"external_load_w": "4.5"
}Charge state values
| Value | State |
|---|---|
| 0 | Off |
| 2 | Fault |
| 3 | Bulk |
| 4 | Absorption |
| 5 | Float |
| 7 | Equalize |
| 245 | Starting |
| 252 | External control |
Once the ESP32 is running, go to Settings → Devices & Services → MQTT. A Victron SmartSolar MPPT device appears with Battery Voltage (V), Battery Current (A), PV Power (W), Yield Today (Wh), Charge State, Error Code, External Load (A) and External Load Power (W). No manual YAML.
Dashboard card — dashboard.yaml is ready to paste into
Dashboard → Edit → Add Card → Manual. It needs two HACS frontend plugins:
Mushroom and
Mini Graph Card.
Template sensors — configuration_template.yaml adds two
optional calculated sensors: Garage Net Battery Power (current × voltage in watts,
positive = charging) and Garage Battery Status (Charging / Discharging / Idle). Add the
template: block to your configuration.yaml and reload YAML.
| Device | Idle draw |
|---|---|
| Raspberry Pi 4 | ~3–5 W |
| ESP32 (this firmware) | ~0.15 W |
~4W saved overnight is ~40Wh per 10-hour night — roughly 3–4Ah at 12V, which is a real fraction of a small leisure battery.
├── include/
│ ├── example.config.h template — copy to config.h
│ └── victron_ble.h BLE parser header
├── src/
│ ├── main.cpp WiFi, MQTT, BLE scanning, FreeRTOS tasks
│ └── victron_ble.cpp AES decryption and MPPT data parser
├── dashboard.yaml ready-made Home Assistant dashboard card
├── configuration_template.yaml optional template sensors
└── platformio.ini build config
PlatformIO handles all of these:
- NimBLE-Arduino — lightweight BLE stack
- PubSubClient — MQTT client
- ArduinoJson — JSON serialisation
- mbedtls — AES, bundled with the ESP32 Arduino core
- victron-ble — the Python library this follows; still the right answer on a Pi or Linux box
- esphome-victron_ble — ESPHome component, if you prefer YAML
- Victron_BLE_Advertising_example — the original Arduino BLE example
MIT.
If this got a Raspberry Pi out of your solar setup, you can buy me a coffee.
