Table of Contents:

1. Introduction

1.1 What is SW3L-NB NB-IoT Flow Sensor

The Dragino SW3L-NB is a NB-IoT Flow Sensor. It detects water flow volume and uplink to IoT server via NB-IoT network. User can use this to monitor the water usage for buildings.

The SW3L-NB will send water flow volume every 20 minutes. It can also detect the water flow status and send Alarm, to avoid the waste for water usage such as broken toilet case.

SW3L-NB is designed for both indoor and outdoor use. It has a weatherproof enclosure and industrial level battery to work in low to high temperatures.

SW3L-NB supports different uplink methods including MQTT, MQTTs, UDP & TCP for different application requirement, and support uplinks to various IoT Servers.

SW3L-NB supports BLE configure and OTA update which make user easy to use.

SW3L-NB is powered by 8500mAh Li-SOCI2 battery, it is designed for long-term use up to several years.

SW3L-NB has optional built-in SIM card and default IoT server connection version. Which makes it works with simple configuration.


1.2 ​Features

  • NB-IoT Bands: B1/B2/B3/B4/B5/B8/B12/B13/B17/B18/B19/B20/B25/B28/B66/B70/B85 @H-FDD
  • Ultra-low power consumption
  • Upload water flow volume
  • Monitor water waste
  • Multiply Sampling and one uplink
  • Support Bluetooth v5.1 remote configure and update firmware
  • Uplink on periodically
  • Downlink to change configure
  • 8500mAh Battery for long term use
  • Nano SIM card slot for NB-IoT SIM

1.3 Specification

Common DC Characteristics:

  • Supply Voltage: 2.5v ~ 3.6v
  • Operating Temperature: -40 ~ 85°C

NB-IoT Spec:

NB-IoT Module: BC660K-GL

Support 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
  • B28 @H-FDD: 750MHz
  • B66 @H-FDD: 2000MHz
  • B70 @H-FDD: 2000MHz
  • B85 @H-FDD: 700MHz


  • 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: 10uA @ 3.3v
  • Max transmit power: 350mA@3.3v

1.4 Flow Sensor Spec

Probe #DW-004DW-006DW-010DW-020
DiameterG1/2" / DN15G3/4" / DN20G1"  / DN25G2" / DN50
Working Range1~30L/min1~60L/min2~100L/min10~300L/min
Measure450 pulse = 1 L390 pulse = 1 L64 pulse = 1 L12 pulse = 1 L
Power Consumption1uA, 3.6v (Sensor Only)1uA, 3.6v (Sensor Only)1uA, 3.6v (Sensor Only)1uA, 3.6v (Sensor Only)
Max Pressure≤ 1.75Mpa≤ 1.75Mpa ≤ 1.75Mpa≤ 1.75Mpa
Temperature range<80°C<80°C<80°C<80°C
Humidity Range35%~90%RH (no frost)35%~90%RH (no frost)35%~90%RH (no frost)35%~90%RH (no frost)

1.5 Applications

  • Flow Sensor application
  • Water Control
  • Toilet Flow Sensor
  • Monitor Waste water

1.6 Sleep mode and working mode

Deep Sleep Mode: Sensor doesn't have any NB-IoT 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.

1.7 Button & LEDs


Behavior on ACTFunctionAction
Pressing ACT between 1s < time < 3sSend an uplink

If sensor has already attached to NB-IoT network, sensor will send an uplink packet, blue led will blink once.
Meanwhile, BLE module will be active and user can connect via BLE to configure device.

Pressing ACT for more than 3sActive Device

Green led will fast blink 5 times, device will enter OTA mode for 3 seconds. And then start to  attach NB-IoT network.
Green led will solidly turn on for 5 seconds after joined in network.
Once sensor is active, BLE module will be active and user can connect via BLE to configure device, no matter if device attach NB-IoT network or not.

Fast press ACT 5 times.Deactivate DeviceRed 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.

1.8 BLE connection

SW3L-NB 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.

1.9 Pin Definitions , Switch & SIM Direction


1.9.1 Jumper JP2

Power on Device when put this jumper.

1.9.2 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

1.9.3 Reset Button

Press to reboot the device.


1.9.4 SIM Card Direction

See this link. How to insert SIM Card.

1.10 Mechanical





Probe Mechanical:

004: DW-004 Flow Sensor: diameter: G1/2” / DN15.  450 pulse = 1 L


006: DW-006 Flow Sensor: diameter: G3/4” / DN20.  390 pulse = 1 L


010: DW-010 Flow Sensor: diameter: G 1” / DN25.   64 pulse = 1 L


020: DW-020 Flow Sensor: diameter: G 2”/ DN50.  12 pulse = 1 L


2. Use SW3L-NB to communicate with IoT Server

2.1 Send data to IoT server via NB-IoT network

The SW3L-NB is equipped with a NB-IoT module, the pre-loaded firmware in SW3L-NB 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 SW3L-NB.

Below shows the network structure:


There are two version: -GE and -1D version of SW3L-NB.

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 SW3L-NB send data to IoT server.

  • Install NB-IoT SIM card and configure APN. See instruction of Attach Network.

Below shows result of different server as a glance.

ServersDash BoardComments




General UDPRaw Payload. Need Developer to design Dash Board 
General MQTTRaw Payload. Need Developer to design Dash Board 





1D Version: This version has 1NCE SIM card pre-installed and configure to send value to DataCake. User Just need to select the sensor type in DataCake and Activate SW3L-NB and user will be able to see data in DataCake. See here for DataCake Config Instruction.

2.2 ​Payload Types

To meet different server requirement, SW3L-NB supports different payload type.


User can specify the payload type when choose the connection protocol. Example:

AT+PRO=2,0            // Use UDP Connection & hex Payload

AT+PRO=2,5            // Use UDP Connection & Json Payload

AT+PRO=3,0            // Use MQTT Connection & Json Payload

AT+PRO=3,1           // Use MQTT Connection & ThingSpeak

AT+PRO=3,3            // Use MQTT Connection & ThingsBoard

AT+PRO=3,5            // Use MQTT Connection & Json Payload

AT+PRO=4,0            // Use TDP Connection & hex Payload

AT+PRO=4,5            // Use TDP Connection & Json Payload

2.2.1 General Json Format(Type=5)

This is the General Json Format. As below:

{"IMEI":"866207058378443","Model":"SW3L-NB","alarm:":0,"pulse":0,"water_flow":0.00,"battery":3.556,"signal":24,"1":{0.14,2023/10/20 06:35:40},"2":{0.14,2023/10/20 06:20:40},"3":{0.14,2023/10/20 06:05:40},"4":{11359.75,2023/10/20 03:50:05},"5":{11359.75,2023/10/18 08:32:45},"6":{11068.47,2023/10/18 08:17:45},"7":{21845.51,2023/10/18 08:02:45},"8":{21845.51,2023/10/18 07:47:45}}


Notice, from above payload:

  • Alarm, Pulse, Water Flow , Battery & Signal are the value at uplink time.
  • Json entry 1 ~ 8 are the last 1 ~ 8 sampling data as specify by AT+NOUD=8  Command. Each entry includes (from left to right): Water Flow, Sampling time.

2.2.2 HEX format Payload(Type=0)

This is the HEX Format. As below:

f866207058378443 1164 0de4 14 00 00 00 00 01c2 0000003d 65321751 004e004e 6531f8ed 004e004e 652f982d 004c004c 652f94a9 0096004f 652f9125 0096004f 652f8da1 0092004f 652f89ce 0092004f 652f864a 004d004d 652f8065


If we use the MQTT client to subscribe to this MQTT topic, we can see the following information when the NB sensor uplink data.



These bytes include the hardware and software version.

Higher byte: Specify Sensor Model: 0x11 for SW3L-NB

Lower byte: Specify the software version: 0x64=100, means firmware version 1.0.0

BAT (Battery Info):

Ex1: 0x0dda = 3546mV

Signal Strength:

NB-IoT Network signal Strength.

Ex1: 0x15 = 21

0        -113dBm or less

1        -111dBm

2...30 -109dBm... -53dBm

31      -51dBm or greater

99      Not known or not detectable

PA4: Support digital level input below 3.3V

00 --> PA4 is at low level.

01 --> PA4 is at high level.

PB15: Support digital level input below 3.3V

00 --> PB15 is at low level.

01 --> PB15 is at high level.


00-->Normal uplink.

01-->Water flow abnormal alarm.


MOD=0 --> Uplink Total Pulse since factory

MOD=1 --> Uplink total pulse since last uplink. 



The calculate flag is a user defined field, total pulse divided by this mark is the converted water flow rate.

Example:in the default payload:

  • calculate flag=450: for SW3L-004 Flow Sensor: 450 pulse = 1 L

  • calculate flag=390: for SW3L-006 Flow Sensor: 390 pulse = 1 L

  • calculate flag=64: for SW3L-010 Flow Sensor: 64 pulse = 1 L

Default value: 450.  



The total pulse generated by the flow of water passing through the water meter.



Unit Timestamp Example: 650abc40(H) = 1695202368(D)

Put the decimal value into this link( to get the time.

2.2.3 ThingsBoard Payload(Type=3)

Type3 payload special design for ThingsBoard, it will also configure other default server to ThingsBoard.

 {"IMEI": "866207058378443","Model": "SW3L-NB","alarm:": 0, "pulse": 198,"water_flow": 0.44,"battery": 3.551, "signal": 22}


2.2.4 ThingSpeak Payload(Type=1)

This payload meets ThingSpeak platform requirement. It includes only five fields. Form 1~5 are:

Distance, Battery & Signal. This payload type only valid for ThingsSpeak Platform

As below:

field1=Total_pulse value&field2=Water_sum value&filed3=Alarm value&filed4=Battery value&field5=Singal value


2.3 Test Uplink and Change Update Interval

By default, Sensor will send uplinks every 2 hours & AT+NOUD=8

User can use below commands to change the uplink interval.

AT+TDC=600        // Set Update Interval to 600s

User can also push the button for more than 1 seconds to activate an uplink.

Note: When SW3L-NB is reset and AT+MOD=0, the total pulse will be read from the latest recorded data as the initial value.

To save battery life, SW3L-NB will sample Water Flow data every 15 minutes and send one uplink every 2 hours. So each uplink it will include 8 stored data + 1 real-time data. They are defined by:

  • AT+TR=900        // The unit is seconds, and the default is to record data once every 900 seconds (15 minutes, the minimum can be set to 180 seconds)
  • AT+NOUD=8     //  The device uploads 8 sets of recorded data by default. Up to 32 sets of record data can be uploaded.

The diagram below explains the relationship between TR, NOUD, and TDC more clearly:


2.5 Alarm for continuously water flow

This feature is to monitor and send Alarm for continuously water flow.

Example case is for Toilet water monitoring, if some one push toilet button, the toilet will have water flow. If the toilet button has broken and can't returned to original state, the water flow will keep for hours or days which cause huge waste for water.

To monitor this faulty and send alarm, there are two settings:

  • Stop Duration: Unit: Second

Default: 15s, If SW3L-NB didn't see any water flow in 15s, SW3L-NB will consider stop of water flow event.


  • Alarm Timer: Units: Minute; Default 0 minutes (means Alarm disable)

Example: 10 minutes, if SW3L-NB detect a start of water flow event and didn't detect a stop event within Alarm timer, SW3L-NB will send an Alarm to indicate a water flow abnormal alarm. 

So for example, If we set stop duration=15s and Alarm Timer=10minutes. If the toilet water flow continuously for more than 10 minutes, Sensor will send an alarm to platform. 

Note: After this alarm is send, sensor will consider a stop of water flow and count for another new event. So if water flow waste last for 1 hour, Sensor will keep sending alarm every 10 minutes.


AT Command to configure:

  • AT+PTRIG=15,10   --> Set Stop duration: 15s, Alarm Timer: 10 minutes. 

  • AT+ PTRIG=0,0  --> Default Value, disable water waste Alarm.


2.6 Set Power Output Duration

Control the output duration 5V . Before each sampling, device will

1. first enable the power output to external sensor,

2. keep it on as per duration, read sensor value and construct uplink payload

3. final, close the power output.

AT Command: AT+5VT

Command ExampleFunctionResponse
AT+5VT=?Show 5V open time.0
AT+5VT=0Normally closed 5V power supply.OK
default setting
AT+5VT=1000Close after a delay of 1000 milliseconds.




2.7 Set the calculate flag

Feature: Set the calculate flag


Command ExampleFunctionResponse
AT+CALCFLAG =450Set the calculate flag to 450.OK
AT+CALCFLAG =390Set the calculate flag to 390.OK
AT+CALCFLAG =64Set the calculate flag to 64.OK
AT+CALCFLAG =12Set the calculate flag to 12.OK


2.8 Set count number

Feature: This setting can clear the pulse count to 0 or set it to a custom value.


Command ExampleFunctionResponse
AT+ SETCNT =0Clear the count value to 0.OK
AT+ SETCNT =100Set the count number to 100.OK


3. Configure SW3L-NB

3.1 Configure Methods

SW3L-NB supports below configure method:


3.2 AT Commands Set

AT+<CMD>?           : Help on <CMD>

AT+<CMD>                      : Run <CMD>

AT+<CMD>=<value>      : Set the value

AT+<CMD>=?          : Get the value

General Commands       

AT                    : Attention        

AT?                  : Short Help      

ATZ                 : MCU Reset     

AT+TDC          : Application Data Transmission Interval

AT+CFG          : Print all configurations

AT+MODEL    :Get module information

AT+SLEEP       :Get or set the sleep status

AT+DEUI                  : Get or set the Device ID

AT+APN     : Get or set the APN

AT+5VT           : Set extend the time of 5V power   

AT+PTRIG      :  Get or Set Alarm for continuously water flow

AT+MOD       :   Get or Set the work mode of device

AT+CALCFLAG    : Get or Set the calculate flag

AT+SETCNT       : Get or set the count at present

AT+PRO          : Choose agreement

AT+RXDL        : Extend the sending and receiving time

AT+TR    : Get or set data record time

AT+CDP     : Read or Clear cached data

AT+NOUD  : Get or Set the number of data to be uploaded

AT+DNSCFG   : Get or Set DNS Server

AT+CSQTIME  : Get or Set the time to join the network 

AT+DNSTIMER  : Get or Set the NDS timer 

AT+TLSMOD  : Get or Set the TLS mode 

AT+GETSENSORVALUE   : Returns the current sensor measurement

AT+SERVADDR :   Server Address

UDP Management

AT+CFM  :    Upload confirmation mode (only valid for UDP)

MQTT Management

AT+CLIENT               : Get or Set MQTT client

AT+UNAME              : Get or Set MQTT Username

AT+PWD                  : Get or Set MQTT password

AT+PUBTOPIC          : Get or Set MQTT publish topic

AT+SUBTOPIC          : Get or Set MQTT subscription topic


AT+FDR              : Factory Data Reset

AT+PWORD        : Serial Access Password

AT+LDATA           : Get the last upload data

AT+CDP               : Read or Clear cached data

4. Battery & Power Consumption

SW3L-NB 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

User can change device firmware to::

  • Update with new features.
  • Fix bugs. 

Firmware and changelog can be downloaded from : Firmware download link

Methods to Update Firmware:

  • (Recommended way) OTA firmware update via BLE: Instruction.


6. FAQ

6.1 How can I access t BC660K-GL AT Commands?

User can access to BC660K-GL directly and send AT Commands.

See BC660K-GL AT Command set

6.2 How to configure the device through the MQTT subscription function?

Subscription content: {AT COMMAND}


Setting AT+5VT=500 through Node-RED requires MQTT to send the content {AT+5VT=500}.


The serial port displays:


7. Order Info

Part Number: SW3L-NB-XX-YY


  • GE: General version ( Exclude SIM card)
  • 1D: with 1NCE* 10 years 500MB SIM card and Pre-configure to DataCake server

1NCE SIM Card NB-IoT network coverage: Austria, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, Finland, Germany, Great Britain, Greece, Hungary, Ireland, Italy, Latvia, Malta, Netherlands, Norway, Puerto Rico, Russia, Slovak , Republic, Slovenia, Spain, Sweden, Switzerland, Taiwan, USA, US Virgin Islands

YY: Flow Sensor Model:

  • 004: DW-004 Flow Sensor: diameter: G1/2”/ DN15.  450 pulse = 1 L
  • 006: DW-006 Flow Sensor: diameter: G3/4”/ DN20.  390 pulse = 1 L
  • 010: DW-010 Flow Sensor: diameter: G1”/ DN25.   64 pulse = 1 L
  • 020: DW-020 Flow Sensor: diameter: G2”/ DN50.  12 pulse =   1 L


8. ​Packing Info

Package Includes:

  • SW3L-NB NB-IoT Flow 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
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