In this post i am excited to share about the new super tiny form factor GPS tracking device we designed for pet tracking and hidden installation applications. The device is so small that it can easily fit in constrained places like inside laptops or expensive machinery and gadgets.
We designed this application based on demands from people who have used VALTRACK-V2 in their applications and found that a smaller device would serve their needs better.
– Someone wanted the VALTRACKs to perform as a PET tracker which can be fit in collars of pets like cats and dogs.
– A wild life expert wanted to put these devices on long interval and long life tracking mode and track wild animal migration paths
– Some wanted to put these devices into their expensive laptops so that they can track and recover them when needed.
This new miniature formfactor device is called VALTRACK-V2MF since its an offset of VALTRACK-V2 in miniature formfactor. The size of the device is only 32mmx18mm.
Here is what we did to get the size down to this levels.
GPS Module : The major contributor to the size reduction is the GPS module, which was changed to this new part SE868K3AL made by Telit. It is very thin and probably the smallest GPS/GNSS module with built in antenna available in market right now. There is another same size variant SE868K7AL which supports only GPS instead of GNSS.
Cellular module : Since the goal was to keep the size as small as possible, we had to go for 2G quadband SIM800C module which is cheap and super small of the size of 17mmx15mm.
Power supply : The device works on 3.7V LiPo batteries which can be charged by the given 2 pin through hole connector. The battery connector is also a through hole connector of 2.54mm pitch. The battery charger used is MCP73831 SOT package chip which can charge batteries at the rate of 100 to 500mA programmable charge rate.
Microcontroller: The MCU is the same STM32L051 series MCU with 64KB of flash memory, enough to fit any kind of GPS tracking application. The MCU is also footprint compatible with a STM32L4 series MCU which we tested for communicatin with Google IOT core using TLS1.2 encryption and JWT generation on the MCU using Mbed TLS library.
Accelerometer : The board has MMA8652 accelerometer made by NXP semicondutors, it was chosen because of the 2mmx2mm small size.
Storage : A TSSOP package 1Mbit EEPROM is added which is used for storing configuration data and GPS logs which couldnt be sent to the server due to unavailability of the cellular network.
Flex connector for debugging : The USB connector was removed in this board in favor of a 10 pin super thin FLEX connector from TE connectivity. Its half the size of the micro USB connector and provides 10 lines out of the board which include the MCU SWD lines for flashing the MCU and USB lines of SIM800C for flashing its firmware and UART lines of MCU for seeing GPS data.
Flex Antenna : The cellular antenna connector is a U.FL connector which can be used for connecting flex antenna as used in the V2 and V2B for size constrained applications.
SIM card connector : A push-push type nano sim connector is added for easy sim insertion and removal.
Power flow control : Two power MOSFETS are added for turning the GSM and GPS module ON and OFF
Test results :
The device worked straight out of the box without any problems as its a proven and tested design and only change was the GPS module and the Flex connector both didnt pose any kind of problems and we were able to load all the firmware configurations on the device like the,
– Long interval tracking application where the device send location pings once per hour or once per day etc.
– Continous tracking mode where device keeps sending location data non stop
– Motion triggered tracking where device sends location only on movement
– SMS tracking mode where device keeps waiting for SMS with only GSM ON
We did get some results with a small 350mAH battery about the same size of the device, and here are the test results.
Device ran for 48 hours sending 1 ping per hour by HTTP on 350 mAH battery
Device ran for 60 days sending 1 ping per day by HTTP on 350mAH battery
Device ran for 48 hours waiting for SMS command with GSM turned ON on 350mAH battery.
There is no limit on the mAH capacity of the battery you want to use with the device, If you put a 4000mAH battery , the device could run for years in long interval modes. It consumes around 200uA (0.2mA) when in deep sleep.
