Data URI image

Table of Contents:

Data URI image

1. Introduction

1.1 What is DDS20-NB NB-IoT Ultrasonic liquid level Sensor

The Dragino DDS20-NB is a NB-IoT Ultrasonic liquid level sensor for Internet of Things solution. It uses none-contact method to measure the height of liquid in a container without opening the container, and send IoT platform via NB-IoT network.

The DDS20-NB sensor is installed directly below the container to detect the height of the liquid level. User doesn't need to open a hole on the container to be tested. The none-contact measurement makes the measurement safety, easier and possible for some strict situation.  

DDS20-NB uses ultrasonic sensing technology for distance measurement. DDS20-NB is of high accuracy to measure various liquid such as: toxic substancesstrong acidsstrong alkalis and various pure liquids in high-temperature and high-pressure airtight containers.

DDS20-NB supports different uplink methods including MQTT, MQTTs, UDP & TCP for different application requirement, and support uplinks to various IoT Servers.

DDS20-NB supports BLE configure and OTA update which make user easy to use.

DDS20-NB is powered by 8500mAh Li-SOCI2 battery, it is designed for long-term use up to several years.

DDS20-NB has optional built-in SIM card and default IoT server connection version. Which makes it works with simple configuration.

image-20230911140426-2.pngData URI image

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
  • Liquid Level Measurement by Ultrasonic technology
  • Measure through container, No need to contact Liquid
  • Valid level range 20mm - 2000mm
  • Accuracy: ±(5mm+S*0.5%) (S: Measure Value)
  • Multiply Sampling and one uplink
  • Support Bluetooth v5.1 remote configure and update firmware
  • Uplink on periodically
  • Downlink to change configure
  • IP66 Waterproof Enclosure
  • 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 Suitable Container & Liquid

  • Solid Wall container such as: steel, iron, glass, ceramics, non-foaming plastics etc.
  • Container shape is regular, and surface is smooth.
  • Container Thickness:
    • Pure metal material.  2~8mm, best is 3~5mm
    • Pure non metal material: <10 mm
  • Pure liquid without irregular deposition.


1.5 Install DDS20-NB

Step 1 Choose the installation point.

DDS20-NB MUST be installed on the container bottom middle position.

image-20220615091045-3.pngData URI image

Step 2:   Polish the installation point.

For Metal Surface with paint, it is important to polish the surface, first use crude sand paper to polish the paint level , then use exquisite sand paper to polish the metal level to make it shine & smooth. 

image-20230613143052-5.pngData URI image

No polish needed if the container is shine metal surface without paint or non-metal container.

image-20230613143125-6.pngData URI image

Step3:   Test the installation point.

Power on DDS20-NB, check if the blue LED is on, If the blue LED is on, means the sensor works. Then put ultrasonic coupling paste on the sensor and put it tightly on the installation point.

It is necessary to put the coupling paste between the sensor and the container, otherwise DDS20-NB won't detect the liquid level.

After paste the DDS20-NB well, power on DDS20-NB. In the first 30 seconds of booting, device will check the sensors status and BLUE LED will show the status as below. After 30 seconds, BLUE LED will be off to save battery life.

LED Status:

  • Onboard LED: When power on device, the onboard LED will fast blink 4 times which means detect the sensor well.

  • BLUE LED always ON: Sensor is power on but doesn't detect liquid. There is problem in installation point.

  • BLUE LED slowly blinking: Sensor detects Liquid Level, The installation point is good.

DDS20-NB will enter into low power mode at 30 seconds after system reset or power on, Blue LED will be off after that.

Note : Ultrasonic coupling paste  is subjected in most shipping way. So the default package doesn't include it and user needs to purchase locally.

Step4:   Install use Epoxy ab glue.

After ensuring that the ultrasonic coupling paste is applied to the sensor and adheres closely to the mounting point, and the sensor can work normally, add AB epoxy glue.

(Note :The ultrasonic coupling agent is used to help the sensor detect the liquid in the container, and the epoxy AB glue is used to fix the probe. Both need to be used at the same time.)

Prepare Eproxy AB glue.

Put Eproxy AB glue in the sensor and press it hard on the container installation point.

Reset DDS20-NB and see if the BLUE LED is slowly blinking.

image-20230809172509-1.pngData URI image      

Note : 

1: Eproxy AB glue needs 3~ 5 minutes to stable attached. we can use other glue material to keep it in the position.

2: Eproxy AB glue is subjected in most shipping way. So the default package doesn't include it and user needs to purchase locally.

1.6 Applications

  • Smart liquid control solution
  • Smart liquefied gas solution

1.7 Precautions

  • At room temperature, containers of different materials, such as steel, glass, iron, ceramics, non-foamed plastics and other dense materials, have different detection blind areas and detection limit heights.
  • For containers of the same material at room temperature, the detection blind zone and detection limit height are also different for the thickness of the container.
  • When the detected liquid level exceeds the effective detection value of the sensor, and the liquid level of the liquid to be measured shakes or tilts, the detected liquid height is unstable.


1.8 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.

1.9 Button & LEDs

1675071855856-879.pngData URI image

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.

1.10 BLE connection

DDS20-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.

1.11 Pin Definitions , Switch & SIM Direction

image-20230819104805-5.pngData URI image

1.11.1 Jumper JP2

Power on Device when put this jumper.

1.11.2 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

1.11.3 Reset Button

Press to reboot the device.


1.11.4 SIM Card Direction

See this link. How to insert SIM Card.

1.12 Mechanical

1675143884058-338.pngData URI image

1675143899218-599.pngData URI image

1675143909447-639.pngData URI image

Probe Mechanical:

image-20220615090910-1.pngData URI image

image-20220615090910-2.pngData URI image

2. Use DDS20-NB to communicate with IoT Server

2.1 Send data to IoT server via NB-IoT network

The DDS20-NB is equipped with a NB-IoT module, the pre-loaded firmware in DDS20-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 DDS20-NB.

Below shows the network structure:

image-20230911140426-2.pngData URI image

There are two version: -GE and -1D version of DDS20-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 DDS20-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


Data URI image



Data URI image

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


Data URI image



Data URI image


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 DDS20-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, DDS20-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=3,5            // Use MQTT Connection & Json Payload

2.2.1 General Json Format(Type=5)

This is the General Json Format. As below:

{"IMEI":"866207058378443","Model":"DDS20-NB","distance":38,"battery":3.57,"signal":24,"1":{38,2023/09/20 02:51:33},"2":{38,2023/09/20 02:36:33},"3":{0,2023/09/20 02:08:29},"4":{0,2023/09/20 01:27:18},"5":{0,2023/09/20 01:12:19},"6":{0,2023/09/20 00:57:19},"7":{0,2023/09/18 09:58:53},"8":{0,2023/09/18 09:43:53}}

image-20230920110813-4.pngData URI image

Notice, from above payload:

  • Temperature , Humidity , 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): Distance, Sampling time.

2.2.2 HEX format Payload(Type=0)

This is the HEX Format. As below:


image-20230920104818-3.pngData URI image

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

image-20230920104047-2.pngData URI image


These bytes include the hardware and software version.

Higher byte: Specify Sensor Model: 0x0a for DDS20-NB

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

BAT (Battery Info):

Ex1: 0x0dfd = 3581mV

Signal Strength:

NB-IoT Network signal Strength.

Ex1: 0x18 = 24

0        -113dBm or less

1        -111dBm

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

31      -51dBm or greater

99      Not known or not detectable


Ex1: 0x0026 = 38 mm


Unit TimeStamp Example: 650a541d(H) = 1695175709(D)

Put the decimal value into this link ( 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": "DDS20-NB","distance": 40,"battery": 3.55, "signal": 20}

image-20230922095654-1.pngData URI image

2.2.4 ThingSpeak Payload(Type=1)

This payload meets ThingSpeak platform requirement. It includes only four fields. Form 1~3 are:

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

As below:

field1=Distance value&field2=Battery value&field3=Signal value

image-20230920113340-5.pngData URI image

2.3  ​Uplink Payload

DDS20-NB will uplink payload via NB-IoT with below payload format:  

Uplink payload includes in total 21 bytes.


Signal Strength

ModDigital Interrupt Distance(unit: mm)Timestamp

If the cache upload mechanism is turned on, you will receive the payload shown in the figure below.

Frame headerFrame data(1)Frame data(2)F…Frame data(X)

2.3.1  Battery Info

Check the battery voltage for DDS20-NB.

Ex1: 0x0B45 = 2885mV

Ex2: 0x0B49 = 2889mV

2.3.2  Interrupt

This data field shows if this packet is generated by interrupt or not. 


0x00: Normal uplink packet.

0x01: Interrupt Uplink Packet.

2.3.3  Distance

Get the distance. Flat object range 20mm - 2000mm.

For example, if the data you get from the register is 0x06 0x05, the distance between the sensor and the measured object is 

0605(H) = 1541 (D) = 1541 mm.

  • If the sensor value is 0x0000, it means system doesn't detect ultrasonic sensor.
  • If the sensor value lower than 0x0014 (20mm), the sensor value will be invalid.



2.4 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.

Notice: The AT+NOUD feature is upgraded to Clock Logging, please refer Clock Logging Feature

To save battery life, DDS20-NB will sample Distance 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:

1692424376354-959.pngData URI image

2.6 Trggier an uplink by external interrupt

DDS20-NB 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

2.7 Clock logging (Since firmware version v1.2.1)

Sometimes when we deploy lots of end nodes in field. We want all sensors sample data at the same time, and upload these data together for analyze. In such case, we can use clock loging feature.

We can use this command to set the start time of data recording and the time interval to meet the requirements of the specific collection time of data.

  • AT command: AT+CLOCKLOG=a,b,c,d

a: 0: Disable Clock logging.   1: Enable Clock Logging

b: Specify First sampling start second: range (0 ~ 3599, 65535)         // Note: If parameter b is set to 65535, the log period starts after the node accesses the network and sends packets.

c: Specify the sampling interval: range (0 ~ 255 minutes)

d: How many entries should be uplink on every TDC (max 32)




After the node sends the first packet, data is recorded to the memory at intervals of 1 minute. For each TDC uplink, the uplink load will include: battery information + the last 5 memory records (payload + timestamp).


Note: Users need to synchronize the server time before configuring this command. If the server time is not synchronized before this command is configured, the command takes effect only after the node is reset.

2.8 Example Query saved historical records

  • AT command: AT+CDP

This command can be used to search the saved history, recording up to 32 groups of data, each group of historical data contains a maximum of 100 bytes.


2.9 Uplink log query

  • AT command: AT+GETLOG

This command can be used to query upstream logs of data packets.


2.10 Scheduled domain name resolution

This command is used to set up scheduled domain name resolution.

AT command:

  • AT+DNSTIMER=XX   // Unit: hour

After setting this command, domain name resolution will be performed regularly.

3. Configure DDS20-NB

3.1 Configure Methods

DDS20-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+CFGMOD           : Working mode selection

AT+DEUI                  : Get or set the Device ID

AT+INTMOD            : Set the trigger interrupt mode

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

AT+PRO          : Choose agreement

AT+RXDL        : Extend the sending and receiving time

AT+DNSCFG   : Get or Set DNS Server

AT+GETSENSORVALUE   : Returns the current sensor measurement

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

AT+CDP     : Read or Clear cached data

AT+SHTEMP:   Get or Set alarm of temp

AT+SHHUM:   Get or Set alarm of moisture

AT+SERVADDR :   Server Address

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

DDS20-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

7.  Trouble Shooting

7.1  Why i always see 0x0000 or 0 for the distance value?

DDS20-NB has a strict installation requirement. Please make sure the installation method exactly follows up with the installation requirement. Otherwise, the reading might be always 0x00.

If you have followed the instruction requirement exactly but still see the 0x00 reading issue, please. please double-check the decoder, you can check the raw payload to verify.


8. Order Info

Part Number: DDS20-NB-XX


  • 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

9. ​Packing Info

Package Includes:

  • DDS20-NB NB-IoT Ultrasonic liquid level 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

10. 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


Copyright ©2010-2022 Dragino Technology Co., LTD. All rights reserved
Dragino Wiki v2.0