S31-FB/S31B-FB – NB-IoT/LTE-M Temperature & Humidity Sensor
1. Introduction
1.1 What is Temperature & Humidity Sensor
The Dragino S31-FB and S31B-FB are NB-IoT/LTE-M Temperature and Humidity Sensor for Internet of Things solution. It is used to measure the surrounding environment temperature and relative air humidity precisely, and then upload to IoT server via NB-IoT or CAT-M1 network.
The temperature & humidity sensor used in S31x-FB is SHT31, which is fully calibrated, linearized, and temperature compensated digital output from Sensirion, it provides a strong reliability and long-term stability. The SHT31 is fixed in a waterproof anti-condensation casing for long term use.
S31x-FB supports different uplink methods include MQTT, MQTTs, TCP or UDP for different application requirement. and Support Uplinks to various IoT Servers.
S31x-FB is powered by 8500mAh Li-SOCI2 battery, It is designed for long term use up to several years. (Real-world battery life depends on the use environment, update period and uplink method. Please check related Power Analyze report).
*make sure you have NB-IoT or CAT-M1 coverage locally.
1.2 Features
- NB-IoT Bands: B1/B2/B3/B4/B5/B8/B12/B13/B17/B19/B20/B25/B26/B28/B65/B66/B85/B106
- CAT-M1 / LTE-M Bands: B1/B2/B3/B4/B5/B8/B12/B13/B18/B19/B20/B25/B26/B28/B66/B85/B106
- Ultra-low power consumption
- External 3 meters SHT31 probe (For S31-FB)
- Measure range -40°C ~ 80°C
- Temperature & Humidity alarm
- Multiply Sampling and one uplink
- Uplink via MQTT, MQTTs, TCP or UDP
- GNSS for Location Report
- Support Bluetooth v5.1 remote configure and update firmware
- Uplink on periodically
- Downlink to change configure
- 8500mAh Li/SOCl2 Battery (S31x-FB)
- Solar panel + 3000mAh Li-ion battery (S31x-FS)
- Nano SIM card slot for NB-IoT SIM
1.3 Specification
Common DC Characteristics:
- Supply Voltage: 2.6v ~ 3.6v
- Operating Temperature: -40 ~ 85°C
Temperature Sensor:
- Range: -40 to + 80°C
- Accuracy: ±0.2 @ 0-90 °C
- Resolution: 0.1°C
- Long Term Shift: <0.03 °C/yr
**Humidity Sensor: **
- Range: 0 ~ 99.9% RH
- Accuracy: ± 2%RH ( 0 ~ 100%RH)
- Resolution: 0.01% RH
- Long Term Shift: <0.25 %RH/yr
NB-IoT Spec:NB-IoT Module: nRF9151-NGFFSupport Bands:
- B1 @H-FDD: 2100MHz
- B2 @H-FDD: 1900MHz
- B3 @H-FDD: 1800MHz
- B4 @H-FDD: 2100MHz
- B5 @H-FDD: 860MHz
- B8 @H-FDD: 900MHz
- B12 @H-FDD: 720MHz
- B13 @H-FDD: 740MHz
- B17 @H-FDD: 730MHz
- B18 @H-FDD: 870MHz
- B19 @H-FDD: 870MHz
- B20 @H-FDD: 790MHz
- B25 @H-FDD: 1900MHz
- B26 @H-FDD: 876MHz
- B28 @H-FDD: 750MHz
- B65 @H-FDD: 2155MHz
- B66 @H-FDD: 2000MHz
- B85 @H-FDD: 700MHz
Battery:
- Li/SOCI2 un-chargeable battery
- Capacity: 8500mAh
- Self Discharge: <1% / Year @ 25°C
- Max continuously current: 130mA
- Max boost current: 2A, 1 second
Power Consumption:
- STOP Mode: 14uA @ 3.3v
- Max transmit power: 350mA@3.3v
1.4 Applications
- Smart Buildings & Home Automation
- Logistics and Supply Chain Management
- Smart Metering
- Smart Agriculture
- Smart Cities
- Smart Factory
1.5 Sleep mode and working mode
**Deep Sleep Mode: **Sensor doesn't have any NB-IoT/CAT-M1 activate. This mode is used for storage and shipping to save battery life.
Working Mode: In this mode, Sensor will work as NB-IoT Sensor to Join NB-IoT network and send out sensor data to server. Between each sampling/tx/rx periodically, sensor will be in IDLE mode), in IDLE mode, sensor has the same power consumption as Deep Sleep mode.
1.6 Button & LEDs
| Behavior on ACT | Function | Action |
|---|---|---|
 1~3s | Send an uplink | If sensor has already attached to NB-IoT/CAT-M1 network, sensor will send an uplink packet, blue led will blink once. |
 >3s | Active Device | Green led will fast blink 5 times, device will enter OTA mode for 12 seconds. And then start to attach NB-IoT/CAT-M1 network. |
 x5 | Deactivate Device | Red led will solid on for 5 seconds. Means device is in Deep Sleep Mode. |
Note: When the device is executing a program, the buttons may become invalid. It is best to press the buttons after the device has completed the program execution.
1.7 BLE connection
S31x-FB support BLE remote configure and firmware update.
BLE can be used to configure the parameter of sensor or see the console output from sensor. BLE will be only activate on below case:
- Press button to send an uplink
- Press button to active device.
- Device Power on or reset.
If there is no activity connection on BLE in 60 seconds, sensor will shut down BLE module to enter low power mode.
1.8 Pin Definitions , Switch & SIM Direction
1.8.1 Jumper JP2
Power on Device when put this jumper.
Power off device when take out this jumper
1.8.2 BOOT MODE / SW1
1)ISP: upgrade mode, device won't have any signal in this mode. but ready for upgrade firmware. LED won't work. Firmware won't run.
2)Flash: work mode, device starts to work and send out console output for further debug
1.8.3 Reset Button
Press to reboot the device.
1.8.4 SIM Card Direction
See this link. How to insert SIM Card.
1.9 Hardware Variant
| Model | Photo | Probe Info |
|---|---|---|
S31-FB |
| 1 x SHT31 Probe Cable Length : 3 meters |
S31B-FB |
| 1 x SHT31 Probe Installed in device. |
2. Use S31x-FB to communicate with IoT Server
2.1 Send data to IoT server via NB-IoT/CAT-M1 network
The S31x-FB is equipped with a NB-IoT module, the pre-loaded firmware in S31x-FB will get environment data from sensors and send the value to local NB-IoT network via the NB-IoT module. The NB-IoT network will forward this value to IoT server via the protocol defined by S31x-FB.
Below shows the network structure:
There are two version: -GE and -1T version of S31x-FB.
GE Version: This version doesn't include SIM card or point to any IoT server. User needs to use AT Commands to configure below two steps to set S31x-FB send data to IoT server.
- Install NB-IoT SIM card and configure APN. See instruction of Attach Network.
- Set up sensor to point to IoT Server. See instruction of Configure to Connect Different Servers.
Below shows result of different server as a glance.
| Servers | Dash Board | Comments |
| Node-Red |
| |
| DataCake |
| |
| Tago.IO | ||
| General UDP | Raw Payload. Need Developer to design Dash Board | |
| General MQTT | Raw Payload. Need Developer to design Dash Board | |
| ThingSpeak |
| |
| ThingsBoard |
|
1T Version: This version has 1NCE SIM card pre-installed and configure to send value to ThingsEye. User Just need to select the sensor type in ThingsEyeand Activate S31x-FB and user will be able to see data in ThingsEye. See here for ThingsEye Config Instruction.
2.2 Payload Types
To meet different server requirement, S31x-FB supports different payload type.
Includes:
- General JSON format payload (Type=5)
User can specify the payload type when choose the connection protocol. Example:
AT+PRO=2,0 // Use UDP Connection & Json Payload
AT+PRO=3,0 // Use MQTT Connection & Json Payload
AT+PRO=4,0 // Use TCP Connection & Json Payload
Note: The default is AT+QGPS=0 // The GPS function is not enabled. Therefore, the GPS collection time in the following example paylaod does not follow the system time, and the latitude and longitude are 0.
2.2.1 General Json Format(Type=0)
This is the General Json Format. As below:
{"IMEI":"355025934932888","IMSI":"460240275257959","Model":"S31x-FB","fcnt":"3","signal":"31","bat":3.67,"temperature":28.1,"humidity":71.7,"time":"2026-4-28T03:29:02Z","latitude":0.000000,"longitude":0.000000,"gps_time":"00/00/00,00:00:00"}Notice, from above payload:
- Temperature, Humidity, Battery, Signal, fcnt, latitude, longitude & GPS time are the value at uplink time.
Example:
**Device ID(IMEI): **
Ex1: 355025934932888
**SIM Card ID(IMSI): **
Ex1: 460240275257959
Model:
Ex1: S31X-FB
FCNT:
Current number of outgoing packets
Ex1: 3 (This represents the second packet in the uplink.)
BAT (Battery Info):
Ex1: 3.67V
Signal Strength:
NB-IoT Network signal Strength.
Ex1: 310 -113dBm or less
1 -111dBm
2...30 -109dBm... -53dBm
31 -51dBm or greater
99 Not known or not detectable
**Temperature: **
Read: temp = 28.1 degree
Read: temp = -19.3 degrees.
**Humidity: **
Read: Value: 71.7, So 71.7%
TimeStamp & GPS Timestamp
Unit TimeStamp Example: 2026-4-28T03:29:02Z
**Latitude:Example: **0x015a7886(H)=22706310(D)=22.706150
**Longitude: Example: **0x06cf341e(H)=114242590(D)=114.242830
3. Configure S31x-FB
3.1 Configure Methods
S31x-FB supports below configure method:
- AT Command via Bluetooth Connection (Recommended): BLE Configure Instruction.
- AT Command via UART Connection : See UART Connection.
3.2 Serial Access Password
After the Bluetooth or UART connection is successful, use the Serial Access Password to enter the AT command window.
The label on the box of the node will print the initial password: AT+PIN=xxxxxx, and directly use the six-digit password to access the AT instruction window.
If you need to change the password, use **AT+PWORD=**xxxxxx (6 characters), -FB nodes only support lowercase letters.
Note: After entering the command, you need to add a line break, and you can also set automatic line breaks in the Bluetooth tool or UART connection tool.
3.3 AT Commands Set
AT+
AT+
AT+
AT+
General Commands
AT+MODEL : Get module information
AT+CFGMOD : Working mode selection
AT+DEUI : Get or set the Device ID
AT+CFG : Print all settings
AT+SERVADDR: Get or Set the Server address
AT+TDC : Get or set the application data transmission interval in s
AT+INTMOD : Get or Set the trigger interrupt mode (0:input,1:falling or rising,2:falling,3:rising)
AT+APN : Get or set the APN
AT+5VT : Get or Set extend the time of 5V power
AT+PRO : Get or Set usage agreement (2:UDP,3:MQTT,4:TCP)
AT+RXDL : Get or Set the receiving time
AT+EXT : Get or Set Count value
AT+SHTEMP:Get or Set alarm of shtemp
AT+SHHUM:Get or Set alarm of shthum
AT+GETSENSORVALUE : Returns the current sensor measurement
AT+DNSCFG : Get or Set DNS Server
AT+SLEEP : Get or Set the sleep mode
AT+IOTMOD: Configure Network Category to be Searched for under LTE RAT
MQTT Management
AT+CLIENT : Get or Set the MQTT clientID
AT+UNAME : Get or Set the MQTT Username
AT+PWD : Get or Set the MQTT password
AT+PUBTOPIC: Get or set MQTT publishing topic
AT+SUBTOPIC: Get or set MQTT subscription topic
AT+MQOS : Set the QoS level of MQTT
AT+TLSMOD : Get or Set the TLS mode
GPS
AT+GTIME : Extend the time to turn on GNSS
AT+QGPS : Turn off and on GPS
AT+QGTDC : Get or set GPS positioning interval in units of h
Information
AT+FDR1 : Reset parameters to factory default values except for passwords
AT+FDR : Reset Parameters to Factory Default
AT+PWORD : Get or set the System password
AT+LDATA : Get the last upload data
AT+CDP : Read or Clear cached data
AT+PDTA: Print the sector data from start page to stop page
AT+PLDTA: Print the last few sets of data
AT+CLRDTA: Clear the storage, record position back to 1st
AT+GETLOG : Print serial port logs
ATZ : Trig a reset of the MCU
AT+UDPMOD: Get or set UDP working mode
AT+REDPT: Get or Set the function of reconnecting the network to send data
AT+QCOPS: Get or set operator code
AT+DEBUG: Get or Set the debug mode
3.4 Test Uplink and Change Update Interval
By default, Sensor will send uplinks every 20 min.
User can use below commands to change the uplink interval.
AT Command: AT+TDC
Example: AT+TDC=7200 // Set Update Interval to 7200 seconds
Downlink Commands: 0x01
Format: Command Code (0x01) followed by 3 bytes.
Example: 12 hours= 43200 seconds 43200(D)=0xA8C0(H)
Downlink Payload: **01 00 A8 C0** // AT+TDC=43200, Set Update Interval to 12 hours.
Note: User can also push the button for more than 1 second to activate an uplink.
3.5 Set the receiving time
Feature: Extend the receiving time
AT Command: AT+RXDL
Example: AT+RXDL=1000 // Set the receiving time delay to 1000ms
Downlink Commands: 0x03
Format: Command Code (0x03) followed by 3 bytes.
Example: Downlink Payload: **03 00 03 E8 **// AT+RXDL=1000
3.6 Reset
Feature: Trig a reset of the MCU.
AT Command: ATZDownlink Commands: 0x04FF
3.7 +5V
Feature: Set extend the time of 5V power.
AT Command: AT+5VT
Example: AT+5VT=2000 // Set extend the time of 5V power to 2000 ms
Downlink Commands: 0x05
Format: Command Code (0x05) followed by 3 bytes.
Example: Downlink Payload: **05 00 07 D0 **// AT+5VT=2000
3.8 Trigger an uplink by external interrupt
S31x-FB has an external trigger interrupt function. Users can use the PB15 pin to trigger the upload of data packets.
AT command:
- **AT+INTMOD ** // Set the trigger interrupt mode
- **AT+INTMOD=0 ** // Disable Interrupt
- **AT+INTMOD=1 ** // Trigger by rising and falling edge
- **AT+INTMOD=2 ** // Trigger by falling edge
- **AT+INTMOD=3 ** // Trigger by rising edge
Downlink Commands: 0x06
Format: Command Code (0x06) followed by 3 bytes.
Example1: Downlink Payload: **06 00 00 01 **// AT+INTMOD=1
Example2: Downlink Payload: **06 00 00 03 **// AT+INTMOD=3
3.9 Set the QoS level
This command is used to set the QoS level of MQTT.
AT command:
- **AT+MQOS=xx **// 0~2
Downlink command: 0x07
Format: Command Code (0x07) followed by 1 byte.
Ex1: Downlink payload: 0x0700 // AT+MQOS=0
Ex2: Downlink payload: 0x0701 // AT+MQOS=1
3.10 Set the TLS mode
Refer to this link (MQTT Connection to send data to Tago.io)to use the TLS mode.
**AT Command: AT+TLSMODExample 1: ** AT+TLSMOD=0,0 // Disable TLS Mode.
Example 2: AT+TLSMOD=1,0 // No authentication
AT+TLSMOD=1,1 // Perform server authentication
AT+TLSMOD=1,2 // Perform server and client authentication if requested by the remote server
Downlink command: 0x09
Format: Command Code (0x09) followed by 2 bytes.
Example1: Downlink Payload: **09 00 00 **// AT+TLSMOD=0,0
Example2: Downlink Payload: **09 01 02 **// AT+TLSMOD=1,2
3.11 Set GTIME open time
Extend the time to turn on GNSS. The automatic GPS location time is extended when the node is activated.
AT Command: AT+GTIME
Example: AT+GTIME=30 // Set the GPS positioning time to 30 seconds
Downlink command: 0x10
Format: Command Code (0x10) followed by 2 bytes.
Example: Downlink Payload: **10 00 1E **// AT+GTIME=30
3.12 Turn on/off GPS
**AT Command: AT+QGPS Ex1: **AT+QGPS=0 // Turn off GPS
**Ex2: **AT+QGPS=1 // Turn on GPS
Downlink command: 0x11
Format: Command Code (0x11) followed by 1 byte.
Example: Downlink Payload: **11 01 **// AT+QGPS=1
3.13 Set QGPS positioning interval
Feature: Set GPS positioning interval (unit: hour).
When GPS is enabled, the node automatically locates and uplinks each time it passes GTDC time after activation.
AT Command: AT+QGTDC
Example: AT+QGTDC=24 // Set the GPS positioning interval to 24h.
Downlink command: 0x12
Format: Command Code (0x12) followed by 3 bytes.
Example: 24 hours: 24(D)=0x18(H)
Downlink Payload: **12 00 00 18 **// AT+QGTDC=24
3.14 Set the IPv4 or IPv6
This command is used to set IP version.
AT command:
- **AT+IPTYPE=1 **// IPv4
- **AT+IPTYPE=2 **// IPv6
3.15 Configure Network Category to be Searched for under LTE RAT.
AT command: AT+IOTMOD=a,b,ca: 0: Disenable eMTC; 1: Enable eMTC
b: 0: Disenable NB-IoT ; 1. Enable NB-IOT
**c:Priority: **If two network categories are enabled simultaneously, the device will give priority to the configured category.
Ext1: AT+IOTMOD=1,1,2 ---->Indicates that both eMTC and NB-IoT are enabled, with priority given to the NB-IoT network type.
3.16 Factory data reset
Two different restore factory Settings configurations.
AT command:
- **AT+FDR **// Reset Parameters to Factory Default.
- **AT+FDR1 **// Reset parameters to factory default values except for passwords.
3.17 Print last few data entries
Feature: Print the last few data entries
AT command: AT+PLDTA
| Command Example | 4 bytes |
|---|---|
| AT+PLDTA=5 Print last 5 entries | 0001 2026/4/28 04:18:17 3371 temp=25.8 hum=62.5 alarm:false 0002 2026/4/28 04:38:18 3363 temp=24.9 hum=62.4 alarm:false 0003 2026/4/28 04:58:18 3363 temp=24.4 hum=61.7 alarm:false 0004 2026/4/28 05:18:18 3359 temp=24.1 hum=60.9 alarm:false 0005 2026/4/28 05:38:18 3363 temp=24.9 hum=60.7 alarm:false OK |
**Downlink Command: **
No downlink commands for feature
3.18 Print data entries base on page
Feature: Print the sector data from start page to stop page.
AT command: AT+PDTA
| Command Example | 4 bytes |
|---|---|
| AT+PDTA=1,1 Print page 1 to 1 | E8000 2026/4/28 03:37:20 3406 temp=28.8 hum=69.5 alarm:false E8010 2026/4/28 03:38:17 3402 temp=29.1 hum=68.0 alarm:false E8020 2026/4/28 03:58:17 3375 temp=28.5 hum=68.4 alarm:false E8030 2026/4/28 04:18:17 3371 temp=25.8 hum=62.5 alarm:false E8040 2026/4/28 04:38:18 3363 temp=24.9 hum=62.4 alarm:false E8050 2026/4/28 04:58:18 3363 temp=24.4 hum=61.7 alarm:false E8060 2026/4/28 05:18:18 3359 temp=24.1 hum=60.9 alarm:false E8070 2026/4/28 05:38:18 3363 temp=24.9 hum=60.7 alarm:false OK |
**Downlink Command: **
No downlink commands for feature
3.19 Clear Flash Record
Feature: Clear flash storage for data log feature.
AT command: AT+CLRDTA
| Command Example | Function | Response |
|---|---|---|
| AT+CLRDTA | Clear date record | Stop Tx events,Please wait for the erase to complete Clear all stored sensor data... Start Tx events OK |
Downlink Command: 0x32
- Example: 0x32 00 // Same as AT+CLRDTA
3.20 Working mode selection
Feature: Set interrupt mode or count mode (PB15 pin).
AT command: AT+CFGMOD
| Command Example | Function |
|---|---|
| AT+CFGMOD=1 | Interrupt mode (default mode) |
| AT+CFGMOD=2 | count mode |
Downlink Command: 0x02
- Downlink command: 02 01 // Equal to AT+CFGMOD=1
- Downlink command: 02 02 // Equal to AT+CFGMOD=2
3.21 Debug mode
Feature: Since the serial communication feature of the NRF9151 module requires activation, this command is intended for users who need to use the serial port for extended periods of time.
AT command: AT+DEBUG
| Command Example | Function |
|---|---|
| AT+DEBUG=1 | Enter debugging mode |
| AT+DEBUG=0 | Exit debugging mode,Serial port function disabled |
Note:1. This feature remains active for only 5 minutes; it will automatically turn off after 5 minutes.2. Keeping the serial port open continuously increases power consumption in sleep mode; the continuous current is 900 μA.
4. Battery & Power Consumption
S31x-FB use ER26500 + SPC1520 battery pack. See below link for detail information about the battery info and how to replace.
Battery Info & Power Consumption Analyze .
5. Firmware update
5.1 Over-the-Air (OTA) Firmware Update via HTTP
Note: Users can upload the firmware binary to any public HTTP server (not a local/private network address) that the device can access, then use the following method to upgrade
Perform the following steps:
① Place the firmware binary (e.g., S31-FB.bin) on an HTTP-accessible server.
② Use a serial port or send the following command to the device: AT#XFOTA=1,"<firmware_url>"
Example:AT#XFOTA=1,"http://repo.dragino.com/release/NB/S31-FB.bin
After the node receives the upgrade command via downlink, it will perform the upgrade automatically as shown below:
5.2 Firmware Update via J-Link Interface
Use this method if OTA is not available or if the device is unresponsive.
**Prerequisites: **
- An ARM emulator (J-Link compatible)
- Firmware update tool: nRF Connect for Desktop
**Note: During the installation of nRF Connect for Desktop, you will be prompted to install the J-Link driver. You must confirm the installation; otherwise, the J-Link external tool will not be recognized. **
5.2.1 Hardware Connection
Remove the NRF9151 module from the motherboard and connect it to the J-Link as illustrated below:
NRF9151 Module Hardware Wiring：
5.2.2 Software Setup
Launch nRF Connect for Desktop.
Locate and download the Programmer tool from the available apps (see below):
After download, click OPEN to enter the Programmer interface.
5.2.3 Firmware Update Steps
Click "SELECT DEVICE" → Select "J-Link"
On the main screen, click "Add file", then click "Browse" and select the firmware you want to update in the pop-up window.
Click “Erase & Write” to begin the update
6. FAQ
6.1 How can I access the nRF9151-NGFF AT Commands?
User can access to nRF9151-NGFF directly and send AT Commands.
See nRF9151-NGFF AT Command set
6.2 General Manual for -FB , -FS models
Users can follow the instructions in this link to see how to configure to connect to different servers.
6.3 Why is there no LED response when I press the button on the solar panel model?
If the LED does not light up when you press the button, it may be because the battery has entered protection mode.
Solution: To reactivate the battery, simply expose the solar panel to direct sunlight. For more details, please refer to: Battery Protection State (Apply to Solar Panel + Li-ion battery)
7. Order Info
Part Number: S31-FB-XX / S31B-FB-XXXX:
- GE: General version ( Exclude SIM card)
- 1T: with 1NCE* 10 years 500MB SIM card and Pre-configure to ThingsEye server
8. Packing Info
Package Includes:
- S31-FB or S31-FB Temperature & Humidity Sensor x 1
- External antenna x 1
Dimension and weight:
- Device Size: 13.0 x 5 x 4.5 cm
- Device Weight: 150g
- Package Size / pcs : 14.0 x 8x 5 cm
- Weight / pcs : 180g
9. Support
- Support is provided Monday to Friday, from 09:00 to 18:00 GMT+8. Due to different timezones we cannot offer live support. However, your questions will be answered as soon as possible in the before-mentioned schedule.
- Provide as much information as possible regarding your enquiry (product models, accurately describe your problem and steps to replicate it etc) and send a mail to Support@dragino.cc.