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Display & Range Extender Protocol

Protocol Overview

This document describes how to interface with the Combustion Display & Range Extender over Combustion’s open source Bluetooth communication protocol.

Bluetooth Advertising

The Display & Range Extender continuously broadcasts advertising packets when powered on. The device supports up to 4 simultaneous incoming BLE connections, and up to 4 simultaneous outgoing BLE connections. If the device has fewer than 4 incoming BLE connections, it will transmit Connectable Advertising packets, otherwise it will transmit Unconnectable Advertising packets.

Advertising Packet Frequency

The device’s advertising interval is dependent on its mode of operation. When one or more associated thermometers are in Instant Read mode, the Display & Range Extender will have an advertising interval of 100ms. Otherwise, the device has an advertising interval of 250ms.

Legacy (BLE 4.0) Advertising Packet

The format of the Advertising packet and scan response are shown in the following tables:

Field
Byte
Value
Manufacturer Specific Data
22
See manufacture specific data

Legacy (BLE 4.0) Scan Response

Field
Byte
Value
Service UUID
16
Node status service UUID

Manufacture Specific Data

Field
Byte
Value
Vendor ID
2
0x09C7 (See Bluetooth company IDs)
Product Type
1
See product type
Serial Number
4
Device serial number
Raw Temperature Data
13
See raw temperature data
Mode/ID
1
See mode and ID data
Battery Status and Virtual Sensors
1
See battery status and virtual sensors
Reserved
2
Reserved for future use

GATT Services and Other Characteristics

The Display & Range Extenders connection interval is dependent on its mode of operation. During normal operation the thermometer expects a connection interval between 400ms and 500ms. While in Instant Read mode, the Display & Range Extender updates its status more often and expects a connection interval between 10ms and 30ms.

The Kitchen Timer implements the following GATT Services and Characteristics.

Device Information Service

This standard BLE service provides static information about the Display & Range Extender. The UUID for the Device Information Service is 0x181A. .

Characteristic
UUID
Description
Properties
Manufacturer Name String
0x2A29
Manufacturer: Combustion Inc
Read
Model Number String
0x2A24
Model: device specific
Read
Serial Number String
0x2A25
Device serial number
Read
Hardware Revision String
0x2A27
Hardware revision
Read
Firmware Revision String
0x2A26
Firmware revision
Read

Node Information Service

Node Status is a custom service that provides the current status of the Display & Range Extender's repeater network. The UUID for the Node Status service is 00000200-CAAB-3792-3D44-97AE51C1407A.

This service has a single characteristic that supports BLE notifications. Each time a new set of measurements is received for a thermometer on the repeater network, the status is sent to each connected device that has subscribed to these notifications. The thermometer status includes the sequence number for first and last record on the thermometer and the current temperature from each sensor.

Characteristic
UUID
Description
Properties
Status
00000201-CAAB-3792-3D44-97AE51C1407A
See Node Status below
Read, Notify

Node Status

Value
Format
Bytes
Description
Message ID
uint32_t
4
Random unique ID for this message, for repeater network propagation
Probe Serial Number
uint32_t
4
Serial number of thermometer for which this the following data pertains.
Log Range
uint32_t
8
Range of logs available on the thermometer. Two uint32_t sequence numbers (min, max).
Current Raw Temperature Data
uint8_t
13
See raw temperature data
Mode/ID
uint8_t
1
See mode and ID data
Battery Status and Virtual Sensors
uint8_t
1
See battery status and virtual sensors
Prediction Status
uint8_t
1
See prediction status
Network Information
uint8_t
1
See network information

UART Service

The UART service is a custom BLE service that emulates a UART. The UUID for the UART service is 6E400001-B5A3-F393-E0A9-E50E24DCCA9E. The RX characteristic is used to receive data and the TX characteristic is used to transmit data via BLE notifications. The format of the data sent and received over this service is described in the UART Messages section.

Characteristic
UUID
Description
Properties
RX
6E400002-B5A3-F393-E0A9-E50E24DCCA9E
Peer device can send data to Thermometer on RX characteristic
Write
TX
6E400003-B5A3-F393-E0A9-E50E24DCCA9E
Thermometer can send data to a peer device on TX characteristic
Read/Notify

UART Command Header

Each message will begin with the same 5 byte header, followed by the message payload.

Value
Format
Bytes
Description
Sync bytes
uint8_t
2
{0xCA, 0xFE}
CRC
uint16_t
2
CRC of message type, payload length, and payload bytes. CRC-16-CCITT (polynomial 0x1021) with 0xFFFF initial value
Message type
uint8_t
1
Payload length
uint8_t
1

UART Response Header

Each response message will include a 7 byte header with the following format.

Value
Format
Bytes
Description
Sync Bytes
uint8_t
2
{0xCA, 0xFE}
CRC
uint16_t
2
CRC of message type, payload length, and payload bytes. CRC-16-CCITT (polynomial 0x1021) with 0xFFFF initial value
Message type
uint8_t
1
Success
uint8_t
1
1 for success, 0 for failure
Payload length
uint8_t
1
Length of the message payload in bytes

UART Messages

The following describes UART Messages relevant to the Display & Range Extender, other UART Messages for the thermometer are described here.

Set Thermometer ID 0x01

After receiving this message, the Display & Range Extender will propagate this message across the repeater network in order to get it to the thermometer referenced by the serial number in the message. Once successfully propagated the thermometer will update its ID in both its Advertising Packet and its Status Characteristic.

Request Payload

Value
Format
Bytes
Description
Thermometer Serial Number
uint32_t
4
Thermometer serial number
New Thermometer ID
uint8_t
1
Thermometer ID (0-7)

Response Payload

The Set Thermometer ID response message has no payload.

Set Thermometer Color 0x02

After receiving this message, the Display & Range Extender will propagate this message across the repeater network in order to get it to the thermometer referenced by the serial number in the message. Once successfully propagated the thermometer will update its color in both its Advertising Packet and its Status Characteristic.

Request Payload

Value
Format
Bytes
Description
Thermometer Serial Number
uint32_t
4
Thermometer serial number
New Thermometer Color
uint8_t
1
Thermometer Color (0-7)

Response Payload

The Set Thermometer Color response message has no payload.

Read Session Information 0x03

After receiving this message the Display & Range Extender will respond with session information for all thermometers on the repeater network.

Request Payload

Value
Format
Bytes
Description
Page
uint8_t
1
Page number to request (0 = first page, 1 = second)

Response Payload

The response payload supports up to 5 thermometers associated with a specific Display & Range extender.

Value
Format
Bytes
Description
Page
uint8_t
1
Page number to request (0 = first page, 1 = second)
Total Pages
uint8_t
1
Total number of pages that can be requested
Thermometer Count
uint8_t
1
Number of thermometer connected to the network
Thermometers on this Page
uint8_t
1
Number of thermometers on this page
N-th Thermometer Device Number
uint8_t
1
N-th thermometer Device Number as shown on Display & Range Extender.
N-th Thermometer Serial Number
uint32_t
4
N-th thermometer serial number (0 = not present)
N-th Thermometer Session ID
uint32_t
4
Random number that is generated when thermometer is turned on, and used to identify logging session.
N-th Thermometer Sample Period
uint16_t
2
Number of milliseconds between each log on N-th thermometer.

Read Logged Data 0x04

After receiving this message the Display & Range Extender will respond with a sequence of Read Log Response messages.

Request Payload

Value
Format
Bytes
Description
Thermometer Serial Number
uint32_t
4
Thermometer serial number
Session ID
uint32_t
4
Random number that is generated when thermometer is removed from charger.
Sample Period
uint16_t
2
Number of milliseconds between each log entry.

Response Payload

Value
Format
Bytes
Description
Thermometer Serial Number
uint32_t
4
Thermometer serial number
Sequence Number
uint32_t
4
Sequence number of the record
Raw Temperature Data
uint8_t
1
See raw temperature data
Virtual Sensors
uint8_t
1
See virtual sensors
Prediction Engine State
uint8_t
1
See prediction engine state

Set Prediction Engine 0x05

After receiving this message and successful response, the probe will enter the specified prediction mode with the specified set point temperature. The probe will update the fields in the Prediction Status of its status characteristic.

Request Payload

Value
Format
Bytes
Description
Thermometer Serial Number
uint32_t
4
Thermometer serial number
Set Prediction Data
uint16_t
2
See set prediction data

Response Payload

The Set Prediction Engine response message has no payload.

Device Connected 0x40

Sent to notify other devices on the repeater network that a device has connected to the network.

Request Payload

Value
Format
Bytes
Description
Product Type
uint8_t
1
Thermometer, repeater node, etc
Thermometer Serial Number
uint32_t
4
Thermometer serial number, if applicable
Node Serial Number
uint8_t
10
Repeater node serial number, if applicable

Response Payload

The Device Connected response message has no payload.

Device Disconnected 0x41

Sent to notify other devices on the repeater network that a device has disconnected from the network.

Request Payload

Value
Format
Bytes
Description
Product Type
uint8_t
1
Thermometer, repeater node, etc
Thermometer Serial Number
uint32_t
4
Thermometer serial number, if applicable
Node Serial Number
uint8_t
10
Repeater node serial number, if applicable

Response Payload

The Device Disconnected response message has no payload.

Read Node List 0x42

Gets information about all Node devices on the repeater network.

Request Payload

Value
Format
Bytes
Description
Page
uint8_t
1
Page number to request (0 = first page, 1 = second)

Response Payload

Value
Format
Bytes
Description
Page
uint8_t
1
Page number to request (0 = first page, 1 = second)
Total Pages
uint8_t
1
Total number of pages that can be requested
Node Count
uint8_t
1
Number of repeating nodes connected to the network
Nodes on this Page
uint8_t
1
Number of thermometers on this page
N-th Node Device Number
uint8_t
1
Used to identify N-th node in topology list (Nodes start at 20)
N-th Node Product Type
uint8_t
1
N-th node’s product type
N-th Node Serial Number
uint32_t
4
N-th node’s serial number (0 = not present)

Read Node List 0x43

Gets information about devices connected to a node on the repeater network.

Request Payload

Value
Format
Bytes
Description
Node Serial Number
uint8_t
1
Node serial number to query

Response Payload

Value
Format
Bytes
Description
Node Device Number
uint8_t
1
Node device number queried (based on node list response)
Node Product Type
uint8_t
1
Product type of this node
Node Serial Number
uint8_t
10
This node's serial number
Inbound Connection Count
uint8_t
1
Number of inbound connections to this node
N-th Inbound Device ID
uint8_t
1
Device number of N-th inbound device (N = 1 to Inbound Connection Count)
N-th Inbound Device RSSI
int8_t
1
RSSI signal strength of N-th inbound device connection
Outbound Connection Count
uint8_t
1
Number of outbound connections to this node
N-th Outbound Device ID
uint8_t
1
Device number of N-th outbound device (N = 1 to Outbound Connection Count)
N-th Outbound Device RSSI
int8_t
1
RSSI signal strength of N-th outbound device connection

Thermometer Session Changed 0x44

Sends notification that a thermometer’s session information changed.

Request Payload

Value
Format
Bytes
Description
Thermometer Device Number
uint8_t
1
Used to index this thermometer and shown on Display & Range Extender or other display nodes (mobile apps, etc)
Thermometer Serial Number
uint32_t
4
Thermometer’s serial number
Thermometer Session ID
uint32_t
4
Random number that is generated when thermometer is turned on

Response Payload

The Thermometer Session Changed response message has no payload.

Common Data Formats