GPS Guided Car

1. GPS Guided Car Mindy Stark Zubair Zerif

3. Original Design • Square shaped car with two sensors on each side • Drawback - Too expensive Top view of Car

4. Original Design • Cylinder shaped car with two sensors • Able to escape three sided trap Top View

5. Current Design • Square shaped car with two sensors Top view

6. Current Design • Sensors are 8 inches above ground • Larger Wheels (8 inches) • Rollers on front and back • Platform on top for GPS

7. Components of Car • Garmin GPS 12XL • Basic Stamp II • 12-Volt stepper motors • Infrared sensors (10 - 80 cm detection range)

8. Driver Circuit • Basic Stamp outputs 5 volts • Stepper motors need 12 volts

9. Basic Stamp / Op-Amp • Vin = 5V • Vout = Vin(1 + R2/R1) = 5(1 + 22/10) = 16V

10. Op-Amp / Mosfet / Motor • Op-Amp output turns the mosfets on and off • Threshold voltage (turn on voltage) is 2 - 4 volts where Vth > VGS - VDS • Maximum needed Vth = 16 - 12 = 4V

11. 12 Volt Stepper Motors • Stepping Sequence (right motor rotates clockwise):

12. IR - Sensors • Sensor will detect objects when requested to do so by logic signal • Measures IR pulse reflection and returns logic signal • Object detection threshold distance can be changed by varying its internal resistance

13. Direction and Angle • Need to know the orientation of the car • GPS provides current location and destination • Possible solutions • Electronic Compass • Using 3 points to triangulate position

14. Destination q Direction and Angle N 2 W E 1 S

15. q F-q Angle to turn = f - q Direction and Angle N 2 f Destination W E S

16. Tan-1 (dy / dx) + 270 dx dy Tan-1 (dx / dy) Tan-1 (dy / dx) + 90 Tan-1 (dx / dy) +180 Implementation of Angle • Use Inverse Tan

17. Problems with Implementation • Basic Stamp has no Tan-1 function • 16 bit words • Basic Stamp doesn’t support decimals

18. Implementation of Angle • Example • dx = 124 • dy = 312 • dx / dy = 0.397 • No decimals allowed = 0

19. Implementation of Angle • Solution: • dx = 124 * 10 • dy = 312 • dx / dy = 3.97 • No decimals = 3

20. Implementation of Angle • 16 bit words • 2 ^ 15 = 32,768 • Need 3 digits for accuracy • Leaves one decimal

21. GPS (Inaccurate) • GPS 12XL (Best accuracy = 13 feet) • More accurate GPS only available • By waterways • In view of the horizon

22. Distance Requirement for 2 Distinct Points • Initial Distance Between points 1 and 2 was 13 feet • Increased to 35 feet (worked well) • Demo day, we used 50 feet Pt. 1 Pt. 2 Pt. 1 Pt. 2 Pt. 1 Pt. 2

23. Stepping Sequence Needs Delay • 25 ms delay between steps for the motor • With no delay, motors draw too much current • Better traction for the wheels

24. Problems with Sensors • 1 sensor stopped working • Range of sensors should be 10 to 80 cm • New sensor didn’t work at a range > 38 cm • Used an average

25. Problems with Sensors • Instructions and code for interfacing with the Basic Stamp from Acroname • Sensor requires 10 to 24 mA • Basic Stamp sources 20 mA per pin, 40 mA total • Used a 5 volt voltage regulator

26. Sensors Motor driver circuit - Basic Stamp output $A Stepper sequence - applied by hand Run motors Turn right, left GPS input Angle algorithm Overall system Testing

27. Improvements(1) • Problem: Car needs to travel long distances for distinct points • Solution: Buy a much better GPS unit • According to Garmin Technical support, a $40,000 unit is required!!!

28. Improvements(2) • Problem: • Vehicle is too slow • Solution: • 1.) Make car lighter • 2.) Use DC motors

29. Improvements(3) • Problem: 8 AA batteries don’t last very long • Solution: Use 12 volt battery that has a longer life.