Ultra low cost navigation system for strategic application – 2018

Project Overview

The project proposes implementation of a low cost navigation system based on the commercially available IMU (Inertial Measurement Unit) module and GPS (Global positioning system) module. Both the modules will be simultaneously calculating the location. For specific strategic applications where the GPS signal may get cut off, IMU module will calculate the position thereafter with a certain integrating error of the dead reckoning system. The error correction will be done once a valid data is obtained from the GPS signal.

Resources

Tiva C series microcontroller : TM4C123GH6PM

PIC microcontroller : PIC18F4550

GPS receiver Neo-06 module

GPS Neo-06 module

GPS receiver module gives output in a standard (National Marine Electronics Association) NMEA string format. It provides output serially on Tx pin with default 9600 baud rate. This NMEA string output from GPS receiver contains different parameters separated by commas like longitude, latitude, altitude, time etc. Each string starts with ‘$’ and ends with carriage return/line feed sequence.

$GPGGA,184241.000,1829.9639,N,07347.6174,E,1,05,2.1,607.1,M,-64.7,M,,0000*7C

Name	Example	Units	Description
Message ID	$GPGGA		GGA Protocol Header
UTC Time	184241.000		hhmmss.sss
Latitude	1829.9639		ddmm.mmmm
N/S Indicator	N		N=North, S=South
Longitude	07347.6174		dddmm.mmmm
E/W Indicator	E		E=East, W=West
Position Fix Indicator	1		Fix GPS SPS mode
Satellites Used	05		Range 0 to 12
HDOP	2.1		Horizontal Dilution of Precision
MSL Altitude	607.1	Meters	Mean Sea Level
Units	M	Meters
Geoid Separation	64.7	Meters
Units	M	Meters
Age of Diff. Corr.	–		Null field if DGPS is not used
Diff. Ref Station ID	0000
Checksum	*7C
Carriage return Line Feed	<CR><LF>		End of message transmission

MPU 6050 module

The MPU module consists of a 3-axis accelerometer, 3-axis gyroscope and temperature sensor.

Gyroscope

The triple-axis MEMS gyroscope in the MPU-60X0 includes a wide range of features: Digital-output X-, Y-, and Z-Axis angular rate sensors (gyroscopes) with a user-programmable fullscale range of ±250, ±500, ±1000, and ±2000°/sec. External sync signal connected to the FSYNC pin supports image, video and GPS synchronization. Integrated 16-bit ADC’s enable simultaneous sampling of gyroscope data. Enhanced bias and sensitivity temperature stability reduces the need for user calibration. It has an improved low-frequency noise performance and a digitally-programmable low-pass filter.

  Operating parameters:
  Gyroscope operating current: 3.6mA  
  Standby current: 5µA

Accelerometer

Digital-output triple-axis accelerometer with a programmable full scale range of ±2g, ±4g, ±8g and ±16g. Integrated 16-bit ADCs enable simultaneous sampling of accelerometers while requiring no external multiplexer. Orientation detection and signaling. User-programmable interrupts and High-G interrupt.

  Operating parameters:
  Accelerometer normal operating current: 500µA  
  Low power accelerometer mode current: 10µA at 1.25Hz, 20µA at 5Hz, 60µA at 20Hz, 110µA at 40Hz

  Configuration registers:
  Device_Address = 0x68 
  PWR_MGMT_1   = 0x6B
  SMPLRT_DIV   = 0x19
  CONFIG       = 0x1A
  GYRO_CONFIG  = 0x1B
  INT_ENABLE   = 0x38
  ACCEL_X = 0x3B
  ACCEL_Y = 0x3D
  ACCEL_Z = 0x3F
  GYRO_X  = 0x43
  GYRO_Y  = 0x45
  GYRO_Z  = 0x47

Block Diagram

Functional block diagram

TM4C123GH6PM test setup

Interfaces diagram

PIC18F4550 test setup

(RTOS is not implemented as a part of this project)

Algorithm

1.Initialize I2C communication.

2.Initialize the baud rate.

3.Initialize the MPU6050 IMU.

4.Read the data Ax, Ay, Az, Gx, Gy and Gz (16 bits each) which is in Q15 format (1.xxxxx).

5.Calculate the displacements along all three axes by integrating Ax,Ay and Az twice with respect to time, thus find the effective displacement magnitude.

6.The direction of displacement is found out by integrating the gyroscope values with respect to time.

5.Thus, compute navigation.

6.Perform serial transmission.

7.Correct the IMU data periodically to remove the error due to integration of noise in IMU.

8.The GPS data is extracted through UART.

Implementation

The system has been implemented on both PIC18F4550 and TM4C123GH6PM. We used TI-RSLK Texas instruments Robotics System Learning kit for evaluation. This kit is programmed for moving in different directions.The on-board navigation system will compute the position each second periodically and sends back to the user. User can press “Update GPS coordinate” for the updating the INS data with GPS.

Source codes

The following link has the codes for implementation of this project in both TM4C123GH6PM and PIC18F4550.

https://github.com/akshaym1995/Embedded-project

Experimental Results

The output window shows the GPS coordinates and also the displacement and orientation using IMU.

Future Scope and Applications

1. Real time scheduling of data acquisition, transmission and processing can be implemented efficiently using RTOS.

2. Implementation of Kalman filter will remove the integrating error of dead reckoning system.

3. This system can be used for strategic space applications, missiles, etc.