Characteristic Formats

●Stable

Detailed encoding for every OWLS characteristic. Verified against Smart Sprout V1.1 firmware.

Primitive Types

Type	Size	Encoding
BLEByte	1 byte	Unsigned 8-bit integer
8-byte char	8 bytes	UTF-8 ASCII string, null-terminated, right-padded
uint32 LE	4 bytes	Little-endian unsigned 32-bit integer
int16	2 bytes	Signed 16-bit integer, little-endian

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LED Control

Color

"FF6B35\0\0"
 ^^^^^^      6 ASCII uppercase hex chars — RRGGBB
       ^^    2 null padding bytes (to fill 8-byte char)

Always uppercase. Parsed with strtoul(buffer, NULL, 16).

Speed

[0x58, 0x02, 0x00, 0x00]  →  600 ms

uint32 little-endian. Value in milliseconds per segment cycle. Read 4 bytes exactly.

Cycle Toggle

BLEByte. 0 = auto-cycle off. Any non-zero value enables auto-cycling.

Cycle Time

"10000\0\0\0"

ASCII decimal string in milliseconds. Parsed with strtoul(buffer, NULL, 10). Default: 10000 (10 seconds).

Not seconds

The firmware stores and expects milliseconds. 10000 = 10 seconds. Sending 10 would give a 10ms cycle.

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Audio Thresholds

All three threshold characteristics share the same encoding:

"3.0000\0\0"

ASCII float string, padded to 8 bytes. Parsed with atof(buffer).

Characteristic	Default	Applied as
Rel Threshold	3.0	dynamic = rollingAvg × relThreshold + offsetThreshold
Offset Threshold	0.0	Fixed value added to the dynamic threshold
Static Threshold	1000.0	Absolute trigger level when Auto Threshold is off

Audio triggers when audio_level > threshold. With Auto Threshold on, the threshold is computed dynamically from the rolling average.

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LED Current (Notify)

"240 mA\0\0"

ASCII string with a space and mA suffix, padded to 8 bytes. Estimated from LED intensity sum:

current (mA) = (intensitySum × 40µA / 1000) + (2mA × ledsEnabled)

The device automatically scales brightness down if current would exceed the configured maximum.

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Battery Level

uint8, 0–100%. Derived from cell voltage using a sigmoid (logistic) function:

percent = 100 / (1 + e^(-14 × (v - 3.7)))

This gives a more linear perceived charge curve than a simple linear map. Voltage is read via a resistor divider (R1 = 100kΩ, R2 = 82kΩ) on the ADC, averaged over 16 readings.

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Temperature

int16. Value = ambient_celsius × 100. Matches the BLE Environmental Sensing spec (unit: 0.01°C).

The firmware offsets the die temperature by −5°C to approximate ambient: ambient = die_temp − 5.0.

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Current Time (0x2A2B)

10-byte packed struct, matching the BLE Current Time Service spec:

Byte(s)	Field	Notes
0–1	Year	uint16 LE
2	Month	1–12
3	Day	1–31
4	Hour	0–23
5	Minute	0–59
6	Second	0–59
7	Day of Week	1=Mon, 7=Sun (ISO 8601)
8	Fractions256	1/256 second fractions
9	Adjust Reason	Bitmask per BLE spec, typically 0

Endianness

Only Year is multi-byte (little-endian). All other fields are single bytes.

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Metadata JSON Formats

Each Metadata characteristic carries a compact JSON string (max 128–256 bytes depending on characteristic). Keys are optional — absent keys mean the capability is not present.

Index

["power", "light", "audio", "sense", "profl"]

Read this first. It lists which metadata characteristics are populated on this device.

Power (META_POWER)

{ "type": "LiPo", "cap": 2000, "io": "USB-C", "v": 5 }

Field	Type	Description
type	string	Battery chemistry — e.g. "LiPo", "li-ion"
cap	number	Capacity in mAh
io	string	Charging connector — e.g. "USB-C", "microusb"
v	number	Charge voltage

Lights (META_LIGHTS)

{ "qty": 60, "type": "WS2812B", "pin": 12 }

Field	Type	Description
qty	number	Number of LEDs
type	string	LED chipset — e.g. "WS2812B", "SK6812"
pin	number	Data pin number

Audio (META_AUDIO)

{ "type": "PDM", "fft": 128 }

Field	Type	Description
type	string	Microphone interface — "PDM", "I2S", "analog"
fft	number	FFT bin count used for analysis

Sensors (META_SENSORS)

{ "audio": true, "mic": "PDM", "motion": false }

Profile (META_PROFILE)

{ "img": "bit.ly/sprout-v1", "ui": "classic", "theme": "#2E7D32", "meta": "https://raw.githubusercontent.com/skyfly200/hyphi-hub/main/public/devices/smart-sprout-v1.1.json" }

Field	Type	Description
img	string	Thumbnail URL for device card in app
ui	string	UI layout hint — "classic", "glowflora-clip", etc.
theme	string	Hex accent color for device card
meta	string	URL to full hosted device profile JSON (optional)

When meta is present, the app fetches the full device profile on first connect and caches it. This allows richer UI data (LED maps, audio viz presets, docs links) without hitting the 256-byte BLE characteristic limit. See Device Profiles →