Summary LED

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.

Ruth Nan, Sydney Saito, Kaichen ZhangDepartment of Electrical and Systems Engineering

Overview

Sensor

Battery Calculations

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.

ULTRASONIC SENSOMETER: THE IMPROVED PARKING METER

References

Figure: LED IV Curve, obtained using NI ELVISmx Instrument Launcher’s Two-Wire Current-Voltage Analyzer (left). Viewing angle drawing (right) from sparkfun.com/datasheets/Components/LED/COM-09590-YSL-R531R3D-D2.pdf

YSL-R531R3D-D2

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.

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.

R. Nan, S. Saito, and K. Zhang. “Ultrasonic Sensometer: The Solution to Parking Meters.” Washington University in St. Louis (2012).

Arduino State Diagram

PING))) Ultrasonic Rangefinder

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).

The traditional parking meter (left) and the add-on that detects the presence of a car and indicates state of the parking meter (right).

¿𝑡 (μ 𝑠) ∙0.0345 𝑐𝑚μ 𝑠

𝑑 (𝑐𝑚 )=𝑡 (μ 𝑠 )29

∙12

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.

State LED Current (mA) Ping Current (mA) Weight (fraction oftime spent in state)

No car 0 0 0.25Paid 0 0 0.7

Warn 0.62 2.83 0.04Overdue 1.86 8.48 0.01

Total Current: 0.242 mA