ULTRASONIC SENSOMETER: THE IMPROVED PARKING METER
Ruth Nan, Sydney Saito, Kaichen Zhang
Department of Electrical and Systems Engineering
Summary
Current methods of monitoring parking meters involve the
inconvenience of parking meter attendants peering into the cloudy
display to determine state of a parked car. Only two states, expired
or paid, are conveyed by the output of the parking meter, causing a
parking meter to display a red background even when cars are not
present.. Our project seeks to improve the parking meter by
detecting the presence of a car at the parking meter, displaying an
LED that is visible from 10 meters, and indicating whether the car is
paid for, about to run out of time, or overdue.
Overview
Goal
• Develop a system that can determine the state of the parking
meter given two boolean signals: whether the parking meter is
paid for and whether there is five minutes or less remaining on
the parking meter.
• Optimize the system by saving power in the design
Approach
• Perform psychophysical analyses of eye visibility thresholds.
• Develop and test algorithms for sensing the presence of the car
using the PING))) Ultrasonic Rangefinder and concurrently
flashing an LED to indicate state.
• Create a model on the Arduino Uno that incorporates our
optimization choices of battery life savings.
Application
• Allowing more efficient parking meters by decreasing time spent
on checking parking meter indicators and adding a five minute
indicator to remind the officer to come back and check the
meter in five minutes.
Sensor
LED
PING))) Ultrasonic Rangefinder
YSL-R531R3D-D2
The PING))) sensor emits a short ultrasonic
burst and then listens for the echo. Sound
travels at 345 m/s at 25˚C. The PING))) sends
out a high pulse as long as the echo has not
come back. To convert the time traveled by the
pulse to the distance from the sample, the code
divides by 29 microseconds (the amount of
time it takes for the sound to travel 1 cm) and 2
(the distance is half of the amount of time
required to travel round trip).
We used a red LED from Sparkfun as the output of our device. Red was chosen
because it denotes an urgent message, signaling the meter attendant to check the
status of the meter.
𝑡 μ𝑠 1
𝑑 𝑐𝑚 =
∙
29 2
𝑐𝑚
= 𝑡 μ𝑠 ∙ 0.0345
μ𝑠
Arduino State Diagram
Figure: LED IV Curve, obtained using NI ELVISmx Instrument Launcher’s TwoWire Current-Voltage Analyzer (left). Viewing angle drawing (right) from
sparkfun.com/datasheets/Components/LED/COM-09590-YSL-R531R3D-D2.pdf
Battery Calculations
The 9V battery supplied by Energizer has 700 mA·h. The Ultrasonic Sensometer
will be used 10 hours a day (7 AM to 5 PM), 5 days a week, and 52 weeks a year. We
aim for the device to last one year, so the average power consumption must be
under 700 mA·h/(10 hr/day*5 days/wk*52 wk/yr) = 0.269 mA. Our devices uses
an average of 0.242 mA, as shown below.
State
LED Current (mA)
Ping Current (mA)
No car
Paid
Warn
Overdue
0
0
0.62
1.86
0
0
2.83
8.48
Total Current:
Weight (fraction of
time spent in state)
0.25
0.7
0.04
0.01
0.242 mA
Acknowledgements
The authors of this poster would like to acknowledge Dr. Robert Morley for his
mentorship, expertise and advice throughout the semester; Professor Ed Richter for
his patience and understanding while helping the authors with the equipment; and
Professor Dennis Mell for his occasional suggestion and help in circuit design.
References
The traditional parking meter (left) and the add-on that detects the presence of a car
and indicates state of the parking meter (right).
R. Nan, S. Saito, and K. Zhang. “Ultrasonic Sensometer: The Solution to Parking
Meters.” Washington University in St. Louis (2012).