AQC-0-0-0-0

The AQC-0-0-0-0 is a CO2 sensor, much like the MH-Z19B. It has the same form factor and is pin compatible. Regarding the protocol it is only compatible with the MH-Z19 for the commands 0x86 and 0x87.

The sensor communicates using TTL serial, 9600 8N1.

Through reverse-engineering a firmware-dump, we've found the following command packet format:

Teardown

• 

  Bottom of PCB, as visible without destroying the sensor

• 

  Top of PCB (inside)

• 

  Case removed

Protocol

• Query: id 01 cc p1 p2 p3 p4 p5 cs

id	Device BUS id? Is 0xFF for our device, but seems variable.
cc	Command (e.g. 0x86)
px	Parameters, left at 00 when there are none
cs	Checksum

Commands

0x86 or 0xC5: Request CO2 level

• Parameters: none.
• Response: FF 86 hh ll 00 00 00 00 cs, where the CO2 level is hh * 256 + ll PPM.
  • Unlike the MH-Z19B, no other info is returned except the CO2 level in PPM.

0x87: Perform manual calibration immediately

• Parameters: none.
• Response: none.
• Implemented by filling the measurement history with the current value and then letting the regular calibration do its magic.

0xC1: Configure

• With p1 set to 0x13 - 0x22: store 16 bit value in p4/p5 in the specific register. We haven't figured any of these out yet.
• With p1 set to 0x32: commit to flash
• With p1 set to 0xAA and p2 set to 0x00: set operation mode to 0
• With p1 set to 0xAA and p2 set to 0x01: set operation mode to 3

0xC2: Set operation mode to 1

• Parameters: none.
• Response: none.

0xC3: Set operation mode to 2

• Parameters: none.
• Response: none.

0xC4: Dump raw measurement

• Parameters: none.
• Response: 5D 00 00 00 01 v1 v1 v1 v1 v2 v2 v2 v2 v3 v3 v3 v3 cs
  • Dumps three 32 bit values, no idea what they are, but we're assuming they're raw sensor values.

0xC5: Same as 0x86

See 0x86.

Operation modes

• 0: Seems to be the same as 3.
• 1: Continuous PPM output on serial as if command 0x86 was given continuously.
• 2: Continuous raw diarrhea mode, keeps sending lots of debug(?) data without checksums.
• 3: Poll mode (default)

Checksum

Same as MH-Z19B.