OPM Parking Meters

Check out our new poster and video (30MB)
Watch our video on youtube: http://www.youtube.com/watch?v=J3UzYLFrjIM.


Andrew IDs - @andrew.cmu.edu

Emily Hart erhart
James Kong jykong
Chris Mar cmar
Kevin Woo kwoo


  • Low-power wirelessly networked parking meters
    • Vehicle detection
    • Find parking spot status using a web interface connected to Google Maps
    • Wireless updates from parking meters to the central server


  • Finding Parking Spaces Is Tedious
    • Drivers waste time and energy searching for open spots
    • Enforcement wastes time checking meters


Technical Specifications

  • Hardware
    • Parking Meters
      • Custom PCB
      • Atmel AVR ATMega168
      • 2 x 16 character LCD Screen
      • Digi XBee 802.15.4
      • Devantech SRF04 Ultrasound Rangefinder
    • Relay Nodes
      • Laptop Computers
      • XBee to USB Dongle
      • (Not yet implemented) Embedded Gumstix with XBee and Wi-Fi
    • Central Server
      • Laptop Computer
  • Software
    • Parking Meters
      • AVR-GCC toolchain
    • Relay Nodes
      • GCC
    • Central Server
      • Apache
      • PHP
      • MySQL
  • Protocols
    • 802.15.4
    • Ethernet, TCP/IP, Wi-Fi


  • Functional
    • Parking meter mounted sensor to detect the presence of a car
    • Parking meter nodes will track car presence and remaining time will be displayed on an LCD
    • Internet connected relay nodes will maintain an up to date aggregate record of parking meter status
    • Parking meter status will be accessible via a web interface


Use Cases

  • Diagrams
  • Cases
    • Car arrives and user pays, car leaves before time runs out
    • Car arrives and user pays, car doesn't leave before time runs out
    • Car arrives and user does not pay, car leaves before being towed
    • Car arrives and user does not pay, user pays before time runs out (this leads back to the first 2 cases)
    • Car doesn't arrive and user pays
    • Car doesn't arrive and user doesn't pay (this is not an interesting case)

System States

Risks & Mitigation Strategies

  • Fundamental
    • Rangefinders do not work for car detection
      • Test a variety of rangefinders
      • Try other types of sensors (weight, etc)
      • Drop this feature
    • Cannot get mesh networking up and running
      • Research other network architectures (tree/star topology)
    • Relay nodes have technical issues
      • Use a laptop
  • Ancillary
    • Nodes use too much power
      • Investigate low-power sensors
      • Use external power supply
      • Make all nodes routers
      • Use custom protocol with forced sleep
    • Cannot get payment protocol (card swipe, authentication) working
      • Use cash / a button
    • Rain/Snow/Precipitation causes interference problems
      • Construct durable housing for nodes
      • Find rangefinders that can handle this
    • Smartphone display infeasible
      • Use custom pages
      • Use normal browsers
      • Display available spots with a list (sorted by block?)

Error Handling

  • Sensor Node goes down
  • Relay Node goes down
  • Server goes down
  • Hardware Failures
    • Rangefinder
      • No response signal after trigger
        • ERROR: bad read
        • Try multiple times
        • Flag as broken after several tries, stop polling
      • Readings below distance threshold for too long
        • ERROR: Obstruction
        • Flag as obstructed, requires "maintenance"
        • Unflag if no longer below threshold
    • Money (Coins, Buttons)
      • Receive too many interrupts
        • ERROR: Jam
        • Flag as broken, requires "maintenance"
        • Disable interrupt
        • Periodically enable interrupt, unflag if OK
      • No Interrupts
        • Nothing we can do about this
    • Battery
      • Voltage drops below threshold
        • ERROR: Low power
        • Send signal to relay node / server
        • Flag for maintenance


Test Cases



Fun Stuff


opm_poster.ppt - OPM Poster (19.5 MB) Chris Mar, 04/27/2009 11:59 pm

opm_poster.pdf - OPM Poster (1.51 MB) James Kong, 04/28/2009 12:07 am

opm_vid_final.wmv (30.4 MB) Chris Mar, 04/30/2009 03:51 pm

opm_smartphone_meters_714x273.jpg (38.5 KB) James Kong, 05/01/2009 04:51 pm