Ultrasonic Distance Sensor

Ultrasonic Distance Sensor

Ultrasonic Distance Sensor

• Like SONAR!
• Sends 40 KHz sound pulses (higher than human hearing)
• Waits for return sound wave (“echoes” or bounces off nearby objects)
• Distance to object can be calculated

Uses

• Auto-range finder
• Self-parking cars
• Obstacle avoidance
• Autonomous vehicles
• Fun fact: This is how dolphins and bats navigate

Parameters

• Operating range

  • Officially: 2 cm - 4 m (1 in - 13 ft)
  • More reliable range: 5 cm - 2 m (2 in - 6.5 ft)

• Angle

  • 15 degrees

Sensor Pins

Sensor	Photon 2	Function
GND	GND	Ground
VCC	VUSB	Power (requires 5v, but will work with 3.7V LiPo battery)
TRIG	Output Pin	start output pulse sequence
ECHO	Input Pin	receive reflection response

Timing Diagram

Timing Part 1: Trigger

• Output sequence
  • LOW for 2 microseconds
  • HIGH for 10 microseconds
  • LOW

delayMicroseconds(<<DELAY_VAL>>);

• Sensor sends out 8 sonic pulses

Timing Part 2: Echo

• Sensor “listens” for sound wave to reflect / bounce off object
• When sound wave reflection is received, echo pin goes HIGH for duration of reflection, then goes LOW
• In order to measure the time it takes for an input to be received, use the pulseIn()

Measure Time with pulseIn

• Syntax

//measure time in microseconds
//returns 0 if no signal received after 3 seconds
int time = pulseIn(<<PIN>>, <<VALUE>>); 

• Example

//Start timing when D2 is HIGH
//Stop timing when D2 is LOW
int time = pulseIn(D2, HIGH); 

Calculating Distance

• pulseIn retuns the time for a signal to reach the nearest object and return
• How do we calculate the distance? Let’s start with cm
• Speed of sound @ 20°C (68 ° F) = 343.5 m/s

Cautions

• Sound waves can reflect off surfaces in room can give incorrect readings
• For example, air conditioning vents and other nearby ultrasonic sensors can cause interference
• There should be 500 ms delay between readings

Lab

• Download project: Go to https://bit.ly/ProjectZip
• Paste the following link into the top right https://github.com/reparke/ITP348-Physical-Computing/tree/main/_exercises/week11/ultrasonic_oled_start

Lab

• Connect the ultrasonic distance sensor
• Using the serial monitor, display
  • Error message when out of range
  • Warning message when less than 5 inches
  • Distance message otherwise

Wiring Diagram

Sensor Wiring

Sensor	Photon 2
GND	GND
VCC	VUSB
TRIG	D6
ECHO	D5

OLED	Photon 2
GND	GND
3V3	3V3
SDA (Blue)	SDA
SCL (Yellow)	SCL

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Credit

• Sparkfun
• Sensor Datasheet