Designing a Low cost NBIOT GPS tracking device – VALTRACK-NBIOT

This is an update post on the miniature GPS tracking device VALTRACK-NBIOT designed for NBIOT network operation.

This device is based on VALTRACK-V2 GPS Tracker and very closely resembles it. The functionalities also remain same except that it operates on the LTE NBIOT network compared to the 2G based VALTRACK-V2.

Size : The form factor remains the same as VALTRACK-V2 50mmx18mm.

Operating voltage : Runs on 3.7V Li-Ion or Li-Po battery charged by a 5Vto 12V power source.

Battery connector : V2 did not have battery connector on the board but this device has an on board 2.54mm JST assembly connector and we can connect standard Li-Po batteries or Li-Ion batteries which come with standard JST connectors. The connector addition makes it easy to design the outside casing as there will be no wires coming of the board.

Charging interface : Like VALTRACK-V2 we have added the MP2617 battery charger chip on this board which will help in charging the battery through given micro USB connector. USB port will support standard cell phone chargers with micro USB cable giving 5V DC.

Microcontroller : The is used also same, STM32L051 series chip with UFQFPN32 package. This is the same chip which was used on the VALTRACK-V2 and VALTRACK-V2B devices.

Motion sensor : LIS3D accelerometer is added which will bring motion sensing and power saving capabilities to the device.

Connectivity : In this board we are using SIMCOM made SIM7020E module, this module supports LTE NBIOT network on bands B1,B3,B5,B8,B20 and B28.

The operating voltage of this module is 2.1 to 3.6V. We are running the module at 3.3V operating voltage because we get standard regulators available at this voltage The module needs about 1.5amps of peak current during transmission so we selected the regulator accordingly.

Compared to other cellular networks like 2G, 3G and 4G modules, NBIOT modules operate at a lower voltage and consume very low current during operation.

Level translator :

Strange things I have observed about GSM module is that they run at a higher voltage, but their IO levels are running at a lower voltage. SIM7020E runs at 3.3V and IO levels of it UART lines and the GPIO is 1.8V. So, we are using this 1.8V to 3.3V bidirectional voltage level translator of TXS series of TEXAS instruments. The TXS chip will translate the 3.3V IO levels of MCU, UART and GPIO lines to 1.8V lines before going to the module and vice versa.

SIM card slot : The same push pull type nano SIM card slot present in the VALTRACK-V2 is provided here.

Antenna :  The device has a  U.FL connector which can be used to connect flex antenna. A Whip type antenna can also be used with the help of a SMA to U.FL connector extension.

For this application we must use Flex antenna because of the size constraints.

Data storage :  

The new addition to the hardware is the FRAM chip, this will help in saving the permanent data like configuration parameters and GPS logs. GPS pings which failed or could not be sent to the server can be stored on EEPROM and  forwarded later when network is available.

    Earlier designs used EEPROM for data saving purpose, they did the job well but still the EEPROM was slower and has lesser write cycles. For saving GPS pings we need a memory which is not worn easily. FRAM was chosen because it is sustain higher write cycles and is faster compared to the EEPROM.

    When the requirement was to save data repeatedly we can use the FRAM chip and if it’s normal usage application then we will be using EEPROM.  This is possible because both the EEPROM chip and FRAM chip are pin and firmware compatible. We don’t need to change any firmware or the commands to write or read from FRAM or EEPROM.

Why we designed this board ?

We designed this board because we got a requirement from Australia for a tracking device which can be fit on live saving or swimming jackets. The device was supposed to operate on TELSTRA NBIOT network and it has to track the people who go swimming in the beaches. The device will be used by coast guards or rescue services who will be monitoring people on the beaches through GPS trackers installed in the life saving jackets.

Hurdles faced :

   Once we got the requirement the design was completed very quickly, and assembling was also done in on time. The problem started when it was time to test the device. In India there is no commercially available NBIOT network yet. All network providers are still in testing phase for NBIOT.

So we designed this device with the help of SIMCOM support as they had promised of getting us early access to NBIOT network once our hardware is ready. The network providers in India like Airtel, Vodafone and Jio are all having testing facilities for NBIOT network since they are doing testing themselves at specific locations. We were supposed to get access for early testing easily as promised by SIMCOM.

Airtel testing facility visit :

As per the discussion the first operator they recommended was Airtel and Airtel had facility in Bangalore as it was nearer to us, we planned a trip with team and visited Airtel office in

    We were given special SIMCARDs for NBIOT testing and two days passed without module registering  to the network and we were informed that SIMCARD was not activated due to some internal communication gap then they told it will take about 3-4 working days to get the SIM card commissioned. Then after two days of wasting our time, we were informed that SIMCARD is activated and when we started testing that device again, it had the same result and did not register to network and we had to return back without any progress on the device testing. We were really upset with Airtel and SIMCOM support because they had wasted about 4-5 days of our time without proper preparation.

Vodafone testing facility visit :  

One month later and after 15 days of mail exchange with SIMCOM and Vodafone we got the appointment to perform testing of devices at their Domlur site in Bangalore. We visited Bangalore and started testing. This testing was done in a park because there is no indoor testing facility at that place, they have just installed a tower outdoors and we are supposed to test outdoors wherever we get place. So, because it was an outdoor testing site, we just found some place started testing. Again to our surprise this SIMCARD was not working and it was not able to register to the network. Then after contacting them they told that there is issue with SIMCARD activation. Even though they took couple of hours, they activated the SIMCARD and it worked.

Test results :

 Further development and testing of device was done here and data arrived on our server quite faster as compared to the 2G network. We observed that latency in server response time was very low and responses arrived almost instantly. I guess LTE NBIOT network provides a significant improvement over the 2G network by proving speed improvement and reduction in power consumption. Here is a short video of testing done and you can see device sending data to our server.

    We tested this device for about 500m away from the tower location and the device was still working fine and sending the data to our server even if the antenna removed. I think the signal was strong enough where we were testing and gave range of 650m.

Firmware specs :             

Firmware features of this device are same as the VALTRACK-V2 GPS tracker. The GPS data can updated to server over HTTP or TCP. In our testing  we have tested only HTTP as of now.  So if you buy one you will get a HTTP based  tracking device which will send data to the server on HTTP post requests. NBIOT networks don’t support SMS because when we have tested at Vodafone site it did not allow us to send SMS. 

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