# Performance Enhancement of Consumer-Grade MEMS Sensors through Geometrical Redundancy
## 4 Realized Prototype of Redundant IMU
### Hardware Architecture  
Method performance has been assessed by means of a suitable prototype of redundant IMU based on low-cost inertial sensors. The redundant inertial measurement unit has been realized by assembling six cost-effective MEMS inertial sensors on cubic support. Each couple of inertial sensors is mounted on a suitable development board, SensorTileTM from STMicroelectronics. The SensorTileTM integrates on a single board a Cortex-M4-based microcontroller characterized by an operation frequency of 80 MHz and a suitable set of motion and environmental sensors. In particular, the board is equipped with a MEMS inertial module (iNemo) that includes a triaxial accelerometer and triaxial gyroscope, whose main nominal specifications are given in [34]. The microcontroller is wired-connected with the iNemo through a traditional SPI (Serial Peripheral Interface) protocol, operating as the master with a serial clock rate equal to 10 MHz. The six SensorTiles have been mounted in the redundant configuration on the faces of a 3-D printed cube made in Acrylonitrile Butadiene Styrene (usually referred to as its acronym, ABS); in particular, an ad hoc Computer Aided Design (CAD) model has been created in order to reduce shrinkage effects and obtain the minimal orthogonality error between adjacent faces (Figure 5).  
Accelerations and angular rates measured by each SensorTileTM are transmitted to a further microcontroller installed on a Nucleo-F303K8 development board and acting as a concentrator of acquired data. Moreover, the connection among concentrator and SensorTiles is carried out by means of the SPI protocol; in this case, the concentrator acts as master of the connection, while the serial clock period has been set equal to 100 ns. Finally, the concentrator provides a Universal Serial Bus (USB) connection with a personal computer for external data transmission and processing as well as a further SPI channel to a Micro-SD (Secure Digital) card adapter module for data saving; to this aim, a proper level shifter has been adopted to match the value of communication voltage between the concentrator and the adapter module.  
The hardware architecture is complemented with a X-NUCLEO-GNSSIA1 by STMicroelectronics, i.e., GNSS expansion board based on Teseo-LIV3F module compliant with ArduinoTM UNO R3 connector [35]. Teseo-LIV3F is a tiny GNSS module supporting the most exploited satellite navigation constellations (Global Positioning System, GPS, BeiDou, Galileo, etc.). The GNSS module is mounted on a NucleoF401 RE development  
Figure 5: Prototype developed.  
board, whose microcontroller acts as an interface between the Teseo-LIV3F module and the concentrator. In particular, GNSS module is activated to provide the National Marine Electronics Association (NMEA) message $PSTMPVS containing information about the current time, position, and speed [35]. The message is received by the microcontroller through a universal asynchronous receiver/transmitter serial (UART) protocol, operated with a baud-rate equal to 9600 bps. The microcontroller forwards the NMEA message to the concentrator by means of a further UART connection with a baud rate equal to 115.2 kbps. To suitably reduce transmission duration, the microcontroller filters out all the messages received by the GNSS module but the one containing the information required by the proposed navigation algorithm.