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Wireless Positioning System. Compiled by Austin Stoker ECE 5320 Spring 2012 Dr. Chen. I want a robot lawn mower but I don’t want to bury a wire. What sensor could I use?. GPS. Only accurate to a few meters . Small (1cmx1cmx.2cm) Cheap ($3-$30). Image from Wikipedia /GPS

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wireless positioning system

Wireless Positioning System

Compiled by Austin Stoker

ECE 5320 Spring 2012

Dr. Chen

  • Only accurate to a few meters.
  • Small (1cmx1cmx.2cm)
  • Cheap ($3-$30)

Image from Wikipedia/GPS

Dimensions and prices http://www.semiconductorstore.com/cart/pc/viewprd.asp?idProduct=42046

corrected gps
Corrected GPS
  • Expensive
  • Requires base station.
  • Note: By 2020 (probably sooner) new GPS satellites will make 10cm GPS as cheap as 10m GPS is today.
video sensors
Video Sensors
  • Complex to implement
  • Not highly reliable
acoustic gps
Acoustic GPS
  • Accurate. (~1 inch)
  • Fairly easy to implement
  • Cheap
  • Only works within setup area
  • Requires programming
  • Requires assembly
how aps works
How APS works

Measuring the time in takes to receive a sound signal from 3 different beacons with known locations the sensor can triangulate it’s location. With only 2 bases the position can be found if the robot is supposed to be within the bounds of the bases.

Base #1

Base #2

Base #3

how aps works cont
How APS works (cont.)
  • The robot sends a request via RF transmitter.
  • The RF request is encoded for a specific base. The base responds with a uniquely modulated audio transmission. This is repeated for each base.
how aps works cont1
How APS works (cont.)
  • The robot times the response time of each signal. Calculates the distance to each base and triangulates it’s position.
  • Acoustic sensor/transmitters
    • Murata MA40S4S/R
    • $10 each

Prices from www.mouser.com/

  • Computation board
    • Microchip dsPIC 30F401
    • $7

Prices from www.mouser.com

  • RF transmitters/reciever
    • EasyRadio ~$20-$40


how to use
How to use
  • Accuracy of 1cm or less has been shown. Plenty good for a lawn mower if it is equipped with touch sensors for curbing and such.
how to use1
How to use
  • Avoid interference noise of 40kHz
how to use2
How to use
  • Allow enough time between requesting from station 1 and station 2. At least 30ms per meter of diameter of lawn.


  • Since the beacons positions are known S is known
  • It is simple from the knowledge of the position of the beacons to calculate the h and y and thus pinpoint the location of the robot.



Make sure the

beacons respond




how accurate
How accurate?


z accuracy in 3d
Z accuracy in 3D
  • Z axis accuracy