Texas Instruments | Using Ultrasonic Technology for Smart Parking and Garage Gate Systems | Application notes | Texas Instruments Using Ultrasonic Technology for Smart Parking and Garage Gate Systems Application notes

Texas Instruments Using Ultrasonic Technology for Smart Parking and Garage Gate Systems Application notes
Using Ultrasonic Technology for Smart Parking and
Garage Gate Systems
Esteban Garcia, Current & Position Sensing (CSPS)
Introduction
Automated parking guidance systems help drivers
detect whether a parking spot is occupied or vacant,
which can save the driver unnecessary search time to
find an available spot.
Both drivers and cities benefit from these parking
guidance systems because these systems can reduce
traffic congestion caused by drivers looking for parking
spaces. When a parking spot is vacant in a garage or
parking lot, the guidance systems can also maximize
the revenue of a paid parking area by alerting drivers
about the open spot.
One way to detect whether a parking spot is empty or
occupied is through contactless ultrasonic technology,
as it is reliable in harsh outdoor environments. Gates
to garages can also employ ultrasonic technology to
make the ticketing process fully automated.
Ultrasonic Theory of Operation
Similar to how bats use echolocation to determine the
distance of objects while navigating in-flight at high
speeds, ultrasonic sensors use high-frequency sound
waves that are inaudible to human hearing to
determine the distance between the sensor and the
object. Figure 1 shows how ultrasonic technology
detects objects through reflected sound waves.
The speed of sound increases in hot environments,
but slows down in cooler environments. Equation 1
shows how temperature affects the speed of sound.
§m·
§m·
§ m ·
Speed of Sound ¨ ¸ 331 ¨ ¸ .6 ¨
¸ u Temperature qC
s
s
© ¹
© ¹
© s°C ¹
(1)
Transducer Mounting Considerations
Designers should consider the environment of the
parking location before they mount transducers.
For indoor parking lots, TI recommends to mount the
transducer face-down on the ceiling above the parking
space. Mounting the transducer on the ceiling
eliminates the worry of vehicle load, because the cars
will not drive over the sensor. It also simplifies
installation and wiring because there is no need to drill
holes in the ground for these transducers.
Outdoor parking lots typically do not have ceilings,
however, and these areas are exposed to harsh
environments. TI recommends to mount the sensors
face-up on (or embedded in) the ground. A transducer
must be able to withstand different elements of nature,
which calls for a closed-top transducer.
Designers can also integrate these sensors into
garage gates to detect vehicles entering and exiting
the garage due to the robustness of ultrasonic
technology in outdoor environments. Figure 2 shows
how the transducers were mounted for these
experiments.
Figure 1. Ultrasonic Sensor Theory of Operation
Designers should consider multiple parameters of
ultrasonic theory, such as frequency and temperature,
when determining distance and gathering accurate
results. As frequency increases, the resolution,
directivity, and attenuation increase while the
measurable distance decreases. The speed of sound
is affected by the temperature of the medium the
sound waves travel through.
SLAA911 – August 2019
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Figure 2. Mounting for Vehicle Detection
SPACER
SPACER
Using Ultrasonic Technology for Smart Parking and Garage Gate Systems
Copyright © 2019, Texas Instruments Incorporated
Esteban Garcia, Current & Position Sensing (CSPS)
1
www.ti.com
Field of View
The average width of car parking spaces in America is
between 2.3 m to 2.75 m, and the average width for
motorcycle spaces is 1.2 m. The sensor must be able
to detect a car or motorcycle within the intended space
and not detect the neighboring spaces. Therefore, TI
recommends to use a transducer that has a narrow
field of view.
The body of vehicles are typically made of recycled
steel, which is a material that allows sound waves to
reflect off effectively. However, because some vehicles
have grooves, some of the sound waves may be
deflected in unintended directions.
Figure 5 shows how the MuRata MA58MF14-7N was
able to detect the vehicle at different distances ranging
from 0.5 m to 2.5 m.
The PGA460 ultrasonic transducer driver and signal
conditioner was used for these experiments, paired
with the MuRata MA48MF14-7NN and Steminc
SMATR400H99XDA transducers that have a directivity
of 80° by 35° and 3° by 3° (H° × V°), respectively.
Vehicle Detection Using Ultrasonic Sensors
When a vehicle comes into view of the ultrasonic
sensor, an echo response is observed. Figure 3 shows
how the Steminc SMATR400H99XDA performed when
mounted underneath a vehicle with a ride height of 15
cm.
Figure 5. Vehicle Detection For Garage Gate
Power Consumption
Because these systems will operate throughout the
day, it is important to take power consumption into
consideration. To conserve energy, the system should
sample the parking space in intervals rather than
continuously. By using USART/SPI communication,
the system can quickly sample and yield results while
providing a power-efficient solution, since each sample
interval requires 10.047 ms to power on, communicate
with the transducer, and receive incoming data.
Figure 6 shows data collected from the PGA460 GUI.
Notice how cutting power to the device after the burstlisten interval reduces power consumption.
Figure 3. Occupancy Detection Below Vehicle
Figure 4 shows how the MuRata MA58MF14-7N was
able to detect a car when mounted 0.5 m and 1 m
above the vehicle. In a separate experiment using the
same configurations, the sensor was able to detect a
motorcycle at a distance of 1 m.
Figure 6. Power Optimization
Device Recommendations
Figure 4. Occupancy Detection Above Vehicle
Garage Gate Sensors
When exiting a parking garage, there is usually an arm
that raises and lowers when a vehicle is within view.
Ultrasonic technology is ideal for this application
because of the high reliability of detection, despite
harsh outdoor conditions.
2
The transducers will be exposed to harsh conditions
regardless of the parking lot they are implemented in,
therefore TI recommends that designers use a closedtop monostatic transducer with the PGA460 for reliable
detection results. Table 1 includes a list of collateral
resources to help ensure proper usage of the
BOOSTXL-PGA460, along with compatible
transducers. For more information, go to
ti.com/ultrasonic.
Table 1. Recommended Collateral
COLLATERAL
DESCRIPTION
Application Note
PGA460 Ultrasonic Module Hardware and
Software Optimization
Quick Start Guide
PGA460-Q1 EVM Quick Start Guide
Excel Spreadsheet
PGA460: Air-Coupled Ultrasonic Transducers &
Transformers Listing
Using Ultrasonic Technology for Smart Parking and Garage Gate Systems
Esteban Garcia, Current & Position Sensing (CSPS)
Copyright © 2019, Texas Instruments Incorporated
SLAA911 – August 2019
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