GasCap Tracking Device Fits Inside of a Gasoline Cap — Inspired by Better Call Saul
Ultra-small, ultra-low-power LoRa/LoRaWAN + concurrent GNSS asset tracker.
In an example of reality imitating fiction, Kris Winer of Tlera Corporation developed a tracking device inspired by an episode of "Better Call Saul." GasCap Asset Tracker combines LoRa and GNSS in a package small enough to fit inside an automobile's gasoline cap!
While GasCap Asset Tracker COULD fit inside a typical cap, that is not the intended application. However, at 16 x 62 mm, this compact board could help track mobility devices and animals. Plus, with the low-power design, it can (potentially) run for up to 10 years!
The two main ICs for GasCap Asset Tracker are a Murata CMWX1ZZABZ-078 SOM and u-blox CAM M8Q GNSS (GPS) module. Other devices include an eight megabyte SPI NOR flash chip (for data logging), an STMicroelectronics LIS2DW12 three-axis accelerometer (with wake-on motion), and a Bosch BME280 sensor for measuring the environment's temperature, pressure, and humidity.
The CMWX1ZZABZ-078 SOM contains two chips. First, an STM32L082 microcontroller. This STM32 has an Arm Cortex-M0+ core running up to 32 MHz with 192 kilobytes of flash and 20 kilobytes of SRAM. The second chip is a Semtech SX1276 Lora radio that supports FSK, GFSK, MSK, GMSK, LoRa, and OOK modulations.
GasCap Asset Tracker uses the accelerometer for wake-on motion detection to conserve power. As a result, when sleeping, the board draws only 2 uA! For perspective, Tlera provides an example application that includes a typical activity profile. In that example, if the GNSS module updates the location data every two hours with communication via LoRaWAN every ten minutes, the average current draw during that cycle is less than 250 microamps!
The recommended battery is a non-rechargeable AA-sized Lithium Thionyl Chloride (Li-SOCl2) cell. These have a high-energy density and a very low self-discharge rate. They are also relatively safe designs. Alternatively, you can use the through-hole header for a connector to use a LiPo-style battery instead.
A software-controllable MOSFET with a voltage divider can monitor the battery's voltage without back powering the microcontroller or wasting power.
One trade-off in this design is the limited GPIO. As a result, only power, a few digital pins, I2C signals, and analog input are available through a Molex PicoBlade connector for connections to external hardware. However, for off-the-shelf tracking and logging, no external hardware is required.
Programming GasCap Asset Tracker's STM32 microcontroller is possible over USB using the Arduino IDE. There is also a Tag Connector landing pattern to attach an SWD programmer.
Animal tracking is a popular application for asset tracking devices from Tlera. However, with the compact size of the GasCap Asset Tracker, you could attach it to scooters, bicycles, or anything else that moves!
You can either make or purchase one of these devices. To build one, order boards from OSH Park and use the bill of materials for the parts list. Or, for 89.95 USD before shipping, you can buy an assembled GasCap Asset Tracker from Tlera's Tindie Store. For LoRa, you need to supply an external whip antenna.