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). ultrasonic pressure waves leave sensor (sensor acts like a speaker) ultrasonic wave reflects off object and returns to sensor (sensor acts like a microphone)

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computing distance The Maxbotix sensor measures the time required for the burst of sound to travel to the target and back. The speed of sound is 1,126 𝑓𝑡 𝑠 in dry air at 68°F, which means that sound can travel 1 inch in 74 μs:   𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑=1,126 𝑓𝑡 𝑠 ∙ 12 𝑖𝑛 𝑓𝑡 ∙ 𝑠 1,000,000 𝜇𝑠 = 1 𝑖𝑛 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 2 𝑜𝑛𝑒 𝑤𝑎𝑦 𝑡𝑟𝑖𝑝𝑠 ∙ 1 𝑖𝑛 74 𝜇𝑠

specifications for MB1261 MB 1261 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

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 

Arduino connection to an Arduino MB 1261 DIGITAL ANALOG POWER AREF GND 13 12 PMW 11 PMW 10 PMW 9 8 7 PMW 6 PMW 5 4 PMW 3 2 TX 1 RX 0 RESET 3V3 5V GND GND Vin 0 1 2 3 4 5 DIGITAL ANALOG POWER Arduino

connection to an Arduino

Arduino sketch void setup() { Serial.begin(9600); // use a baud rate of 9600 bps when printing to the monitor } void loop() { int output = analogRead(0); // read the voltage at analog pin 0 int distanceCM = output * 2; // compute distance in centimeters float distanceIN = distanceCM / 2.54; // compute distance in inches float distanceFT = distanceIN / 12.0; // compute distance in feet Serial.println(distanceCM); // print out distance in centimeters on LCD delay(1000); // wait 1000ms between readings }

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); // use a baud rate of 9600 bps when printing to the monitor pinMode(12,OUTPUT); // declare pin 12 as an output for speaker } void loop() { int output = analogRead(0); // read the voltage at analog pin 0 int distanceCM = output * 2; // compute distance in centimeters float distanceIN = distanceCM / 2.54; // compute distance in inches float distanceFT = distanceIN / 12.0; // compute distance in feet int tone_freq = distanceCM*40; // a freq of 40*cm is good tone(12,tone_freq); // send a tone out of pin 12 } digital output (pin 12)