This is an app for ESP32 to decode the signal from Nexus-TH 433MHz thermal sensor.

RXB6 RF receiver is connected to GPIO21 (change it in the code if you need a different pin). RXB6 outputs high level when it detects carrier, low level when it detects no carrier.

That app uses a busy-loop in main to sample GPIO, using interrupts is not feasible since you'd need to service at least 4000 interrupts/second to detect pulses of 500uS.

Nexus-TH uses OOK modulation at 433MHz, basic params:

• pulse is 400-600uS (carrier present)
• preamble is >2000 uS (no carrier)
• end of payload is >3000 uS (no carrier)
• zero is 800-1000 uS (no carrier)
• one is 1650-2150 uS (no carrier)

Signal looks like:

   |--|                  |--|       |--|                 |--|                             |--|
   |  |                  |  |       |  |                 |  |                             |  |
---|  |------------------|  |-------|  |-----------------|  |-----------------------------|  |
   PULSE    PREAMBLE     PULSE ZERO PULSE    ONE              END OF PAYLOAD

Payload is transmitted several times and consists of 36 bits (preamble and EOP are not counted)

AAAAAAAA BX CC DDDDDDDDDDDD EEEE FFFFFFFF, where:

• A - ID
• B - 1 if battery is OK, 0 if battery low
• X - always zero
• C - channel, zero based (0 for channel 1)
• D - temperature * 10 in C. E.g. 123 for 12.3C
• E - Unknown
• F - Humidity. Clamp to 100

Create cfg.toml (see cfg.toml.example) to specify your credentials for WiFi and MQTT

The app will publish JSON with temperature and humidity data, example:

{"time" : "2024-11-02 12:05:31 UTC", "model" : "Nexus-TH", "id" : 174, "channel" : 1, "battery_ok" : 1, "temperature_C" : 10.100, "humidity" : 91}