Transcript living with the lab - Louisiana Tech University

Maxbotix Ultrasonic Distance Sensor
The distance sensor emits short bursts of sound and listens for this sound to echo off
of nearby objects. The frequency of the sound is too high for humans to hear (it is
ultrasonic). The sensor measures the time of flight of the sound burst and
determines distance using the time of flight and the speed of sound (1,126 ft/s).
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2
computing distance
The Maxbotix sensor measures the time required for the burst of sound to travel to the target
𝑓𝑡
and back. The speed of sound is 1,126 in dry air at 68°F, which means that sound can travel
𝑠
1 inch in 74 μs:
𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 = 1,126
𝑓𝑡 12 𝑖𝑛
𝑠
1 𝑖𝑛
∙
∙
=
𝑠
𝑓𝑡 1,000,000 𝜇𝑠
74 𝜇𝑠
Since the sound wave must travel out to the target and back again, a factor of 2 must be
incorporated into distance calculations. If a variable “duration” records the time of flight of the
sound wave, then the distance to the target in inches is computed as follows:
𝑖𝑛𝑐ℎ𝑒𝑠 = 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛 (𝜇𝑠) ∙
𝑟𝑜𝑢𝑛𝑑 𝑡𝑟𝑖𝑝
1 𝑖𝑛
∙
2 𝑜𝑛𝑒 𝑤𝑎𝑦 𝑡𝑟𝑖𝑝𝑠 74 𝜇𝑠
3
specifications for MB1261
•
•
•
•
•
reliable measurement range: 50cm to 10m (20 inches to 35 feet)
supply voltage: 3.3V to 5V (we will use 5V)
frequency: 42kHz (human hearing = 20Hz to 20kHz)
10 readings can be taken per second (10Hz sampling)
analog voltage output of Vcc/1024 for every 2cm (for Vcc=5V and a 10-bit ADC, an output change of 1 = 2cm)
MB
1261
4
11-inch
wide board
beam pattern
sensor can see a 0.25-inch diameter dowel 6-feet away if it is straight ahead
3.5-inch
diameter dowel
1-inch
diameter dowel
0.25-inch
diameter dowel
can’t see me 
5
POWER
0
1
2
3
4
5
RESET
3V3
5V
GND
GND
Vin
AREF
GND
13
12
PMW 11
PMW 10
PMW 9
8
7
PMW 6
PMW 5
4
PMW 3
2
TX 1
RX 0
connection to an Arduino
MB
1261
DIGITAL
ANALOG
6
connection to an Arduino
7
Arduino sketch
void setup() {
Serial.begin(9600);
}
void loop() {
int output = analogRead(0);
int
distanceCM = output * 2;
float distanceIN = distanceCM / 2.54;
float distanceFT = distanceIN / 12.0;
Serial.println(distanceCM);
delay(1000);
// use a baud rate of 9600 bps when printing to the monitor
//
//
//
//
read the voltage
compute distance
compute distance
compute distance
at
in
in
in
analog pin 0
centimeters
inches
feet
// print out distance in centimeters on LCD
// wait 1000ms between readings
}
8
example application
A piezospeaker is installed on the breadboard to allow the device to output an irritating noise whose
frequency is proportional to the distance from the sensor to a target.
void setup() {
Serial.begin(9600);
pinMode(12,OUTPUT);
}
void loop() {
int output = analogRead(0);
int
distanceCM = output * 2;
float distanceIN = distanceCM / 2.54;
float distanceFT = distanceIN / 12.0;
int tone_freq = distanceCM*40;
tone(12,tone_freq);
// use a baud rate of 9600 bps when printing to the monitor
// declare pin 12 as an output for speaker
//
//
//
//
read the voltage
compute distance
compute distance
compute distance
at
in
in
in
analog pin 0
centimeters
inches
feet
// a freq of 40*cm is good
// send a tone out of pin 12
}
digital
output
(pin 12)
9