Turn a cheap Xiaomi LYWSD03MMC humidity monitor into a small live solar display for Home Assistant.
- Big number: current PV production in kW (
5.7) - Small number: how much of it you use at home right now, in % (
98 %) - Face: gets happier the more of your own energy you use
(^_^)
It's handy in the kitchen: one glance tells you whether it's a good moment to run the dishwasher or the washing machine.
No ESP32 and no soldering. Home Assistant talks to the thermometer over the Bluetooth it already has (a Raspberry Pi's built-in Bluetooth works fine).
- Xiaomi Mi Temperature and Humidity Monitor 2 (LYWSD03MMC)
- Home Assistant with a working Bluetooth integration whose adapter can make connections. A local adapter is the tested setup. ESPHome Bluetooth proxies with active connections should work too but haven't been tested.
- Sensors for PV production and grid export (any inverter integration will do)
The stock firmware can't show your own values. The pvvx ATC_MiThermometer custom firmware can, and you flash it over the air from the browser.
- Open the Telink Flasher in Chrome or Edge on a computer with Bluetooth.
- Click Connect and select your thermometer (
LYWSD03MMC). - Click Do Activation and wait for Login successful. The page shows the hardware and firmware version.
- Under Custom Firmware select ATC_v59.bin (or the latest version) and click Start Flashing.
Mine was hardware B1.4, stock firmware 1.0.0_0130. It flashed directly, without going through the original firmware first. Other hardware revisions or newer stock firmware may need extra steps, so check the pvvx README if yours behaves differently.
After flashing, write down the thermometer's MAC address (A4:C1:38:…). You'll need it below.
- HACS → ⋮ → Custom repositories → add
https://github.com/jozefpis/xiaomi-LYWSD03MMC-to-solar-meter, type Integration - Install PVVX Display
Copy custom_components/pvvx_display/ into your Home Assistant config/custom_components/ folder.
Add this line to configuration.yaml and restart Home Assistant:
pvvx_display:Developer tools → Actions, switch to YAML mode:
action: pvvx_display.show
data:
address: "A4:C1:38:XX:XX:XX"
big: 5.7
small: 98
percent: true
happy: true
bracket: true
validity: 65535The display should change within a few seconds.
Self-consumption % = (production − export) / production. See examples/template_sensors.yaml. Just replace the entity IDs with your inverter and grid meter sensors.
See examples/automations.yaml:
- sends the values every 3 min when someone is near the display (motion sensor + person at home), otherwise every 8 min
- sends immediately at the first production in the morning and after an HA restart
- after sunset (or 10 min with no production) shows zeros and stops connecting until the next morning
| Field | Description |
|---|---|
address |
MAC address of the thermometer (required) |
big |
Big number, one decimal place, −99.5 … 1999.5 |
small |
Small number, whole number, −9 … 99 |
validity |
Seconds the display keeps your value instead of its own reading. 65535 = permanently |
unit |
Symbol next to the big number: none, deg_c, deg_f, minus, lowdash, lines, deg_ghe, deg_e |
percent |
Show % next to the small number |
battery |
Show the battery icon |
happy / sad / bracket |
Combine into faces (see below) |
| happy | sad | bracket | Face |
|---|---|---|---|
| ✓ | ✓ | (^_^) |
|
| ✓ | ^_^ |
||
| ✓ | ✓ | Δ△Δ |
|
| ✓ | -∧- |
||
| ✓ | ✓ | (-∧-) |
- The display keeps flipping back to temperature/humidity? Use
validity: 65535. Shorter values (even 900 s) make it alternate between your values and its own reading. In pvvx firmware 4.4+, 65535 means "show only external data until reboot". Downside: if HA stops sending, the display stays frozen on the last value. - There's no kW/W unit on the LCD. Send kilowatts (
4.6), which fits the big field nicely and looks just like the original temperature. - The big field officially goes up to 1999.5, but in practice very large values showed garbage on my unit. Normal PV values (0–15 kW) are fine.
- The small field shows
Hiat 100, so the component caps it at 99. - Battery: every update means one BLE connection. One per minute drains a CR2032 in a few months. Every 3–8 min during the day plus no updates at night is a good compromise.
- One write at a time: the component serializes connections, because many BLE adapters can't handle parallel ones.
- Error
not in Bluetooth range (or not connectable): move the thermometer closer to the adapter or check that your adapter supports active connections.
The component connects via Home Assistant's Bluetooth stack (bleak-retry-connector), writes one 8-byte frame to characteristic 0x1F1F without response and disconnects immediately:
[0] 0x22
[1:3] big number int16 LE, value × 10
[3:5] small number int16 LE
[5:7] validity uint16 LE, seconds
[7] flags bit0 happy, bit1 sad, bit2 bracket, bit3 %, bit4 battery, bits5-7 unit
This is the same frame the ESPHome pvvx_mithermometer display component uses, just sent directly from Home Assistant.
- pvvx/ATC_MiThermometer for the firmware and the flasher, which make all of this possible
- ESPHome
pvvx_mithermometercomponent, used as a reference for the display protocol
MIT