NAVILIGHT ‘A GPS based Embedded System for Backtracking in Unfamiliar Environments’

ABSTRACT

             NAVILIGHT is an embedded system based, innovative flashlight used for navigation.  Its primary function is to record the user's starting point, trace the path taken and display the path back to the user.  This system uses pin-point precision if the user is receiving a GPS signal.  If the user does not receive this signal, the system uses dead-reckoning, where the NAVILIGHT uses software based backtracking to orient the user back to his/her starting point. 

The NAVILIGHT is a flashlight with special features primarily for military use. One of the two primary uses it has is a backtracking system that directs the user back through a maze from where he first began. An example can be if a person had to retrieve something from a dark area with numerous paths such as a cave.  The second use is a GPS system that shows the shortest path back to the given starting point. An example can be if a person were to travel across a forest at night, he can avoid misdirection on the way back by using the GPS system.

The NAVILIGHT will be controlled mainly by an 80C188EB CPU with the first primary function programmed in the C language.  This program will keep track of the direction taken and display the way back on the LCD display.  The embedded system will control the second function of the NAVILIGHT.  The embedded system interfaces with the GPS receiver and outputs the quickest direction or way back on the LCD display. It is also assumed that the user will operate the GPS receiver outside and will be able to acquire signals from at least three satellites.

            The NAVILIGHT also has minor functions that will make it as efficient as possible for the life of it's battery. It will have a sensor that detects the intensity of the light surrounding the NAVILIGHT and will adjust the power to the light bulbs as it sees fit. Depending on the light intensity being low or high, the sensor will increase or decrease the brightness of the bulbs. The NAVILIGHT will shut off automatically if it has been left idle over a period of time. And when there is a need to replace or recharge the battery, the NAVILIGHT will have a low battery indicator.

This project is important because it is a small portable device that is easily controllable. The possibilities for the use of the NAVILIGHT are countless. When the time comes for the NAVILIGHT to be used to its full potential it will have the ability to save lives.

Introduction:

The NAVILIGHT is a flashlight with special features primarily for military use. One of the two primary uses it has is a backtracking system that directs the user back through a maze from where he first began. An example can be if a person had to retrieve something from a dark area with numerous paths such as a cave.  The second use is a GPS system that shows the shortest path back to the given starting point. An example can be if a person were to travel across a forest at night, he can avoid misdirection on the way back by using the GPS system.

The NAVILIGHT also has minor functions that will make it as efficient as possible for the life of it's battery. It will have a sensor that detects the intensity of the light surrounding the NAVILIGHT and will adjust the power to the light bulbs as it sees fit. Depending on the light intensity being low or high, the sensor will increase or decrease the brightness of the bulbs. The NAVILIGHT will shut off automatically if it has been left idle over a period of time. And when there is a need to replace or recharge the battery, the NAVILIGHT will have a low battery indicator.

This project is important because it is a small portable device that is easily controllable. The possibilities for the use of the NAVILIGHT are countless. When the time comes for the NAVILIGHT to be used to its full potential it will have the ability to save lives.

Technical Description:

The NAVILIGHT will be controlled mainly by an 80C188EB CPU with the first primary function programmed in the C language.  This program will keep track of the direction taken and display the way back on the LCD display.  The embedded system will control the second function of the NAVILIGHT.  The embedded system interfaces with the GPS receiver and outputs the quickest direction or way back on the LCD display. It is also assumed that the user will operate the GPS receiver outside and will be able to acquire signals from at least three satellites.

             The intensity of the light will be controlled by a sensor, which supplies more voltage to the light bulbs as it gets darker or less voltage to make it dimmer as more light is present.  One of the minor functions includes a low battery indicator, which will be connected to a LED and will only be turned on when the battery life is low.

The other minor function is the auto shut off which is also controlled by a sensor. This sensor will turn the NAVILIGHT off if there is no activity for a certain amount of time.

The NAVILIGHT is designed to operate in normal weather conditions.

FUNCTIONAL REQUIREMENTS:

Vector 2X Digital Compass

MAGNETO-INDUCTIVE SENSORS

These sensors change inductance with different applied magnetic fields.  It employs a single solenoid winding for each axis.  The frequency of the oscillation changes with the magnetic field.  The output of the sensor circuit is inherently digital, and can be fed directly into a microprocessor.

The Earth's magnetic field is three-dimensional. In the Northern hemisphere the X-Y component of magnetic field vector lies parallel to the Earth's surface and points towards the magnetic north pole, but the majority of the Earth's field vector lies along the Z axis, which points into the ground. Because of this, compasses need to be held level to the Earth's surface in order to be accurate.

The sensors are assumed to be at right angles with respect to each other. Upon initiation of the calibration sequence take two readings from the compass at 180 degrees apart from each other.

We chose the Vector 2X Sensor, shown below, because of its ease of calibration and low power consumption (less than 10 milliamp draw as compared to the 30 milliamp draw for Dinsmore's sensor).  The module itself is 1.5" X 1.3" X 0.3". The pins are on standard

0.1  spacing.  The Vector 2X (V2X) compass delivers high accuracy, low power consumption, and low cost in a small package.  The module delivers 2-degree accuracy with 1-degree resolution, outperforming all compasses in its price range.  In the end, the Vector 2X (V2X) was by far the best choice. The V2X is a 2-axis magnetometer that measures the magnetic field in a single plane. This plane is the plane created by its two sensors, which are perpendicular to each other on the board.

80C188EB CPU (MICRO-CONTROLLER):

The 80C186EB is a second generation CHMOS High-Integration microprocessor. It has features that are new to the 80C186 family and include a STATIC CPU core, an enhanced Chip Select decode unit, two independent Serial Channels, I/O ports, and the capability of Idle or Powerdown low power modes. This micro-controller is having a Turbo Debugger. So the codings can be written in C Language.

M12 Oncore GPS Receiver (Antenna)

 

       Motorola M12 Oncore Global Positioning System Receiver

The M12 Oncore adds more features at both a lower cost and smaller size.  This GPS unit measures 40mm X 60mm X 10mm and draws between 220 milliamps and 250 milliamps.  The M12 can be easily interfaced to a serial receiver.  Once again, this met our requirement of low power consumption. GPS Receiver is operated outside and is able to aquire signals from atleast three satellites.

MPC 201 LCD & Keypad Interface

            LCD interface is required to produce output to the user.  The MPC201 LCD and Keypad Interface features alphanumeric and sub-VGA graphic LCD display interface, pinouts for popular LCD panels, and PC/104 format so it can attach directly to our computer.  This unit was also chosen because it is directly compatible to the SBC1190 microcontroller and the

           The MPC201 LCD and keypad interface allows direct connection to alphanumeric LCD displays (i.e. 2 line by 40 character, etc.). In addition, sub-VGA graphic LCD displays can also be driven if they employ an 8-bit parallel interface. Two LCD connectors are supplied, one normal and one with mirror image pinout. This provides the option of cabling into the top or bottom of the LCD units in tight places, for instance against front panels. The keypad scanner drives rows of switches and senses inputs from columns. Key codes reflect the intersection of row and column. Debounce is provided on-board, so any type of switch can be used in connecting a row line to a column line. Two connectors are provided, each for up to a 4 x 5 matrix of 20 keys.

LIGHT SENSOR

A Smart Q Light Sensor uses a photodiode which produces a voltage proportional to light intensity. It is sensitive to light in the range from 350nm to 700nm. The sensor has a built in infrared rejection filter, giving it a spectral response similar to that of the human eye.

         The Smart Q Light sensors is having high accuracy, precision and consistency. They are supplied calibrated and the stored calibration (in Lux) is automatically loaded when the light sensor is connected.

APPROACH AND DESIGN:

Compass Calibration

Let (Xe,Ye) represent the Earth's magnetic field in any given direction as measured with no interfering magnetic field. The host system will superimpose its additive interfering field, which we can call (Xo,Yo), on top of (Xe,Ye). Let (Xn,Yn) represent the field of a given heading as measured by the sensors in the operating environment, such that it contains the interfering fields as generated by the host system.

Xn = Xe + Xo

Yn = Ye + Yo

So:

Xe = Xn – Xo

Ye = Yn – Yo

(Xe,Ye) represents the true Earth's magnetic field – which is the field that the correct heading can be computed from. Therefore, the offset value (Xo,Yo) needs to be calculated and subtracted from (Xn,Yn) in order to obtain the correct heading information.

Because the compass is fixed with respect to the host system, the readings (X₁,Y₁) and

(X₂,Y₂) taken during calibration will both contain the same (Xo,Yo) values. Since the calibration points are 180° apart, the Earth's magnetic field contained within (X₁,Y₁) and (X₂,Y₂) will be equal but opposite in sign. So we can write:

X₁ = Xe + Xo

Y₁ = Ye + Yo

X₂ = -Xe + Xo

Y₂ = -Ye + Yo

Thus if we add the appropriate equations above and solve for Xo and Yo we find

Xo = (X₁ + X₂)/2

Yo = (Y₁ + Y₂)/2

Xo and Yo are generally constant values that can should be stored and subtracted for each

heading computation performed. Their values will change if the magnetic field of the host

system either increases through magnetization or decreases through demagnetization.

Heading is calculated from Xe and Ye, as follows:

Ae = arctangent(Ye / Xe)

Depending upon the arctangent function implemented, Ae will need to be map into the

correct quadrant. The (Xe,Ye) values correspond to the following quadrants:

  +X, +Y à Ae is between 0° and 90°

-X, +Y à Ae is between 90° and 180°

-X, -Y à Ae is between 180° and 270°     +X, -Y à Ae is between 270° and 360°

GLOBAL POSITIONING SYSTEM:

The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satelllites and their ground stations

The 24 GPS satellites (21 active, 3 spare) are in orbit at 10,600 miles above the earth. The satellites are spaced so that from any point on earth, four satellites will be above the horizon. Each satellite contains a computer, an atomic clock, and a radio. With an understanding of its own orbit and the clock, the satellite continually broadcasts its changing position and time. On the ground, any GPS receiver contains a computer that "triangulates" its own position by getting bearings from three of the four satellites. The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within a few meters.

EMBEDDED SYSTEM:

        Embedded systems involve the miniaturization of electronics so that it can fit into compact devices. It also deals with the software required to drive the associated hardware. Embedded systems contain programmed instructions running via processor chips. We can define as a system where a computing device I embedded into a non-computing device meant for doing some computations. These tasks may range from acquiring (or) transferring data about the work done by mother device to displaying information (or) controlling mother device. Embedded system contains a processor, memory, I/O ports and sensors and many more.