Data Formats

The Multiflexmeter uses a sensor passthrough architecture. The firmware transmits raw sensor data without interpretation. This page documents the data formats used by different sensor modules.

Passthrough Architecture

Sensor Module                    MFM Firmware                    Application
    │                                │                               │
    │ ◄─── CMD_PERFORM (0x10) ───────│                               │
    │                                │                               │
    │ ───── CMD_READ (0x11) ────────►│                               │
    │ ◄──── SMBus Block Read ────────│                               │
    │                                │                               │
    │       Raw bytes (max 32)       │ ───── LoRaWAN FPort 1 ───────►│
    │                                │                               │
    │                                │                    TTN Decoder │
    │                                │                     + Backend │

• Sensor module encodes data in its own format
• Firmware reads up to 32 bytes via SMBus Block Read
• Raw bytes are transmitted on FPort 1
• Application layer (TTN decoder + backend) interprets the data

Common Payload Structure

All sensor modules follow this base structure:

Byte	Field	Description
0	Module Address	I2C address (e.g., 0x36)
1	Module Type	Identifies the sensor type
2+	Module Data	Type-specific payload

Poldermill Sensor (Type 0x01)

Used for monitoring poldermill rotation.

Payload Format

Byte	Field	Description
0	Module Address	0x36
1	Module Type	0x01
2	Flags	Status flags
3-6	Revolutions	uint32 big-endian

Flags Byte

Bit	Name	Description
0	Spinning	1 = Mill is rotating
1	Pumping	1 = Mill is pumping water
2-7	Reserved	Future use

Example Payload

36 01 03 00 00 02 5B

Decoded:

• Module Address: 0x36
• Module Type: 0x01 (Poldermill)
• Flags: 0x03 (spinning=1, pumping=1)
• Revolutions: 603 (0x0000025B)

TTN Decoder

function decodePoldermill(bytes) {
  if (bytes.length < 7) return null;

  var flags = bytes[2];
  var revolutions = (bytes[3] << 24) | (bytes[4] << 16) |
                    (bytes[5] << 8) | bytes[6];

  return {
    module_address: bytes[0],
    module_type: bytes[1],
    spinning: (flags & 0x01) !== 0,
    pumping: (flags & 0x02) !== 0,
    revolutions: revolutions
  };
}

Distance Sensor (Type 0x02)

Used for water level or distance measurements.

Payload Format

Byte	Field	Description
0	Module Address	0x36
1	Module Type	0x02
2-3	Distance	uint16 big-endian (mm)
4-5	Temperature	int16 big-endian (0.1°C)

Example Payload

36 02 03 E8 00 FA

Decoded:

• Module Address: 0x36
• Module Type: 0x02 (Distance)
• Distance: 1000 mm (0x03E8)
• Temperature: 25.0°C (0x00FA = 250 × 0.1°C)

TTN Decoder

function decodeDistance(bytes) {
  if (bytes.length < 6) return null;

  var distance = (bytes[2] << 8) | bytes[3];
  var tempRaw = (bytes[4] << 8) | bytes[5];
  // Handle signed value
  if (tempRaw > 32767) tempRaw -= 65536;

  return {
    module_address: bytes[0],
    module_type: bytes[1],
    distance_mm: distance,
    temperature_c: tempRaw / 10.0
  };
}

Generic Module Format

For custom sensor modules, follow this pattern:

Byte	Field	Description
0	Module Address	I2C address
1	Module Type	Unique type ID
2+	Data	Module-specific

Type Registration

When creating a new sensor module, choose a unique Module Type ID not already in use. Document the payload format for backend developers.

Version Information (FPort 2)

The version ping message uses a special format:

Byte	Field	Description
0	Command	0x10
1-2	Firmware Version	16-bit encoded
3-4	Hardware Version	16-bit encoded

Version Encoding

Bit 15:     Protocol (0=development, 1=release)
Bits 14-10: Major version (0-31)
Bits 9-5:   Minor version (0-31)
Bits 4-0:   Patch version (0-31)

Decoding Example

function decodeVersion(uint16) {
  return {
    protocol: (uint16 >> 15) & 0x01,
    major: (uint16 >> 10) & 0x1F,
    minor: (uint16 >> 5) & 0x1F,
    patch: uint16 & 0x1F
  };
}

Maximum Payload Size

• SMBus Block Read maximum: 32 bytes
• LoRaWAN maximum varies by data rate
• SF12: ~51 bytes
• SF7: ~222 bytes

The firmware reads up to 32 bytes from the sensor module. Larger payloads require multiple transmissions.