Data output

You are reading the 1.3 documentation

The packet format changed in 2.0: timestamp became received_at, lost_data_count became samples_lost, a per-sample timestamps array and a name field were added, and a sifibridge schema subcommand was introduced to export the schemas. None of those apply here. For 2.0 or later, see the current data output reference.

Data Packet Format

SiFi Bridge outputs sensor data as JSON packets (use -p flag for pretty-printed output). Each packet follows a standard structure defined by the DataPacket schema.

DataPacket Structure

{
  "device": "BioPointV1_3",
  "id": "default-1",
  "mac": "00:11:22:33:44:55",
  "packet_type": "ppg",
  "data": {
    "ir": [2738.0, 2753.0, 2765.0],
    "r": [3141.0, 3154.0, 3168.0],
    "g": [3465.0, 3474.0, 3482.0],
    "b": [2890.0, 2903.0, 2915.0]
  },
  "lost_data_count": 0,
  "sample_rate": 100.0,
  "status": "ok",
  "timestamp": 1730370225.123
}

One timestamp per packet, not per sample

1.3 stamps the packet, not the individual samples: there is a single timestamp and no per-sample array. To place samples in time, divide by sample_rate back from the packet timestamp. A per-sample timestamps array arrived in 2.0.

Field Descriptions

Field	Type	Required	Description
device	string	Yes	Device type (e.g., BioPointV1_3, SiFiBand)
id	string	Yes	Device manager name (e.g. default-1)
mac	string	Yes	Device MAC address
packet_type	string	Yes	Type of data in this packet (see Packet Types)
data	object	Yes	Channel data: { "channel_name": [samples...] }
lost_data_count	integer	Yes	Number of samples lost since the previous packet
status	string	Yes	Packet status (see Packet Status)
timestamp	double	Yes	Packet timestamp (Unix epoch seconds)
sample_rate	double	No	Measured rate in Hz. Omitted on packet types with no rate, such as status and start_time, and on the first packet of each sensor

id is the device manager name, not a device identifier — 1.3 addresses hardware through named managers, and SiFi Bridge creates one called default-1 at startup. There is no name field; it was added in 2.0.

Packet Types

The packet_type field indicates what kind of data is in the packet:

Type	Description	Common Channels
ecg	Electrocardiography	ecg
emg	Electromyography	emg
eda	Electrodermal Activity	eda
imu	Inertial Measurement Unit	ax, ay, az, qw, qx, qy, qz
ppg	Photoplethysmography	ir, r, g, b, ppg
emg_armband	EMG Armband (8 channels)	emg0-emg7
temperature	Temperature sensor	temperature
status	Device status update	battery_%
memory	Memory download data	Varies
low_latency	Low-latency mode data	Varies
start_time	Acquisition start time	-
start_packet	Acquisition started	-
device_info	Device information	-

Packet Status

The status field indicates the state of the packet:

Status	Description
ok	Data received successfully
lost_data	Some data samples were lost
recording	Device is recording to memory
memory_download_completed	Memory download finished
memory_erased	Device memory was erased
invalid_datetime	Invalid timestamp
invalid	Invalid/corrupted packet

Channel Names

Available channel names that can appear in the data object:

Biosignal Channels

• ecg - Electrocardiography (heart activity)
• emg - Electromyography (muscle activity)
• eda - Electrodermal activity (skin conductance)

IMU Channels

• ax, ay, az - Accelerometer (g, or 9.81 m/s²)
• qw, qx, qy, qz - Quaternion orientation

PPG Channels

• ir - Infrared LED
• r - Red LED
• g - Green LED
• b - Blue LED

EMG Armband Channels

• emg0 through emg7 - 8-channel EMG armband

Status Channels

• temperature - Device temperature (°C)
• battery_% - Battery level (percentage)
• memory_used_kbytes - On-board memory used (kB)

Start-time Channels

• year, month, day - Acquisition start date

• hours, minutes, seconds - Acquisition start time

  Note these are plural in 1.3; 2.0 renamed them to hour, minute and second.

Device Types

The device field can be:

• BioPointV1_0, BioPointV1_1, BioPointV1_2, BioPointV1_3 - BioPoint versions
• SiFiBand - SiFiBand device
• Invalid - Unknown/invalid device

---

Example Data Packets

PPG Data Packet

{
  "device": "BioPointV1_3",
  "id": "default-1",
  "mac": "AA:BB:CC:DD:EE:FF",
  "packet_type": "ppg",
  "data": {
    "ir": [2738.0, 2753.0, 2765.0],
    "r": [3141.0, 3154.0, 3168.0],
    "g": [3465.0, 3474.0, 3482.0],
    "b": [2890.0, 2903.0, 2915.0]
  },
  "data_timestamps": {
    "ir": [1730370225.123, 1730370225.133, 1730370225.143],
    "r": [1730370225.123, 1730370225.133, 1730370225.143],
    "g": [1730370225.123, 1730370225.133, 1730370225.143],
    "b": [1730370225.123, 1730370225.133, 1730370225.143]
  },
  "data_lost_count": {
    "ir": 0,
    "r": 0,
    "g": 0,
    "b": 0
  },
  "sample_rate": 100.0,
  "status": "ok",
  "timestamp": 1730370225.123
}

IMU Data Packet

{
  "device": "SiFiBand",
  "id": "default-1",
  "mac": "11:22:33:44:55:66",
  "packet_type": "imu",
  "data": {
    "ax": [-0.15, -0.14, -0.16],
    "ay": [0.08, 0.09, 0.08],
    "az": [9.81, 9.80, 9.82],
    "qw": [1.0, 1.0, 1.0],
    "qx": [0.0, 0.01, 0.0],
    "qy": [0.0, 0.0, 0.01],
    "qz": [0.0, 0.0, 0.0]
  },
  "data_timestamps": {
    "ax": [1730370225.200, 1730370225.210, 1730370225.220],
    "ay": [1730370225.200, 1730370225.210, 1730370225.220],
    "az": [1730370225.200, 1730370225.210, 1730370225.220],
    "qw": [1730370225.200, 1730370225.210, 1730370225.220],
    "qx": [1730370225.200, 1730370225.210, 1730370225.220],
    "qy": [1730370225.200, 1730370225.210, 1730370225.220],
    "qz": [1730370225.200, 1730370225.210, 1730370225.220]
  },
  "data_lost_count": {
    "ax": 0,
    "ay": 0,
    "az": 0,
    "qw": 0,
    "qx": 0,
    "qy": 0,
    "qz": 0
  },
  "sample_rate": 100.0,
  "status": "ok",
  "timestamp": 1730370225.200
}

ECG Data Packet

{
  "device": "BioPointV1_3",
  "id": "default-1",
  "mac": "AA:BB:CC:DD:EE:FF",
  "packet_type": "ecg",
  "data": {
    "ecg": [0.85, 0.92, 1.15, 1.45, 1.23, 0.95, 0.88]
  },
  "data_timestamps": {
    "ecg": [
      1730370225.000,
      1730370225.004,
      1730370225.008,
      1730370225.012,
      1730370225.016,
      1730370225.020,
      1730370225.024
    ]
  },
  "data_lost_count": {
    "ecg": 0
  },
  "sample_rate": 250.0,
  "status": "ok",
  "timestamp": 1730370225.000
}

Status Packet with Data Loss

{
  "device": "BioPointV1_3",
  "id": "default-1",
  "mac": "AA:BB:CC:DD:EE:FF",
  "packet_type": "status",
  "data": {
    "battery_%": [87.0],
    "temperature": [36.5]
  },
  "data_timestamps": {
    "battery_%": [1730370225.500],
    "temperature": [1730370225.500]
  },
  "data_lost_count": {
    "battery_%": 0,
    "temperature": 0
  },
  "sample_rate": null,
  "status": "lost_data",
  "timestamp": 1730370225.500
}

Processing Data Packets

For Python, we recommend using sifi-bridge-py.