Support the BME680 sensor on a MCU680 module

BME680 sensor

The BME680 sensor from Bosh Sensortec measures relative humidity, barometric pressure, ambient temperature and gas (VOC). The open source driver provides raw measurements, such as the resistance of the gas sensing element.

The heater element of gas sensor affects the temperature and humidity measurements. Compensated temperature and humidity measurements are available trough a closed source integration library (BSEC). The BSEC provides three air quality estimates derived from raw measurements:

index of air quality (IAQ, 0-500);
CO2 equivalent (eCO2, ppm);
breath VOC (bVOC), ppm).

MCU680 module

The GY-MCU680v1 is a chinese module with an STM32F051K8 mirocontroller (μC) and 3.3V low-dropout regulator (LDO). The μC acts as UART bridge, providing BSEC outputs from the BME680 sensor.

Serial communication

Under factory settings, the serial protocol is UART 9600 8N1 (3.3V/5V TTL). The alternative 115200 BAUD rate will not be not supported.

Commands

A5 55 3F 39: Output all data, factory setting
A5 55 XX YY: Select output data, where
- XX output selection (temperature_flag | rel_humidity_flag | pressure_flag | IAQ_flag|gas_flag | altitude_flag)
- YY message checksum (0xA5+0x55 XX)%0x100
- 01 temperature_flag
- 02 rel_humidity_flag
- 04 pressure_flag
- 08 IAQ_flag
- 10 gas_flag
- 20 altitude_flag
A5 56 02 FD: Automatic output, factory setting
A5 56 01 FC: Query output
A5 58 01 FE: 115200 BAUD rate
A5 58 02 FF: 9600 BAUD rate, factory setting
A5 5A 01 00: Save setup. Save the current settings to flash and restart according to the saved settings.
A5 5A 02 01: Restore setting. Factory setting are restored, the baud rate is 9600, and all data is automatically output.

Message format

Under the factory settings, the module provides 7 values packed on a 20 bit message. The following hexdump (xxd -g1 -c20) shows one message per line

00000000: 5a 5a 3f 0f 09 7d 0a c4 01 8b 89 00 19 00 00 9e f2 00 05 19  ZZ?..}..............
00000014: 5a 5a 3f 0f 09 79 0a c5 01 8b 85 00 19 00 00 a4 83 00 05 a9  ZZ?..y..............
00000028: 5a 5a 3f 0f 09 76 0a c8 01 8b 85 00 19 00 00 ab 32 00 05 5f  ZZ?..v..........2.._
0000003c: 5a 5a 3f 0f 09 74 0a c8 01 8b 87 00 19 00 00 b0 27 00 05 59  ZZ?..t..........'..Y
00000050: 5a 5a 3f 0f 09 72 0a c9 01 8b 87 00 19 00 00 b5 33 00 05 69  ZZ?..r..........3..i
00000064: 5a 5a 3f 0f 09 70 0a d0 01 8b 83 00 19 00 00 ba 05 00 06 42  ZZ?..p.............B
00000078: 5a 5a 3f 0f 09 6f 0a d2 01 8b 83 00 19 00 00 bf 71 00 06 b4  ZZ?..o..........q...
0000008c: 5a 5a 3f 0f 09 6e 0a d0 01 8b 83 00 19 00 00 c3 6e 00 06 b2  ZZ?..n..........n...
000000a0: 5a 5a 3f 0f 09 6c 0a cf 01 8b 85 00 19 00 00 c8 ee 00 05 35  ZZ?..l.............5
000000b4: 5a 5a 3f 0f 09 6a 0a d0 01 8b 83 00 19 00 00 cc b0 00 06 f9  ZZ?..j..............

to do

[x] add new module
[x] add test for message decoding
[x] test on actual hardware
[x] add test for format options
[x] integrate with mqtt/influx services
[x] rewrite module info to conform to sensor docs
[x] update readme

avaldebe / PyPMS