Introduction to Arduino

• Arduino is an open-source prototyping platform used for building electronic projects by processing electrical signals (analog or digital)

• Analog Signals: smooth, continuous curve

  • Range: real numbers

  • Used for temperature, sound intensity, light intensity

  • Used for resistors, capacitors, inductors, diodes, transistors, and operational amplifiers

    • Circuits with these components are analog

    • Can be more difficult to design

  • Susceptible to noise

    • Small voltage variations - can result in processing errors

• Digital Signals: series of discontinuous levels (step function)

  • Range: real numbers

  • Width of the step is determined by sampling rate

    • Faster sampling rate = reduced step width and increased signal accuracy

    • Music sampling range is from 8 kHz to 22.6 MHz

  • Used for signals for microcontrollers

  • Signals have different logic levels

    • High: 5V, 3.3V, 1,8V

    • Low: 0V

  • Easier to design than analog circuit but more expensive

• Analog and Digital Conversion

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  • Signal quality is lost during conversion

    • Analog to digital conversion is done by measuring voltage at equally spaced points in time (sampling rate)

    • Faster sampling rates reduce width of step, which increases accuracy of conversion

• Arduino Uno

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• Wire Color Conventions

  • Black: ground

  • Red: 5V

  • Orange: 3.3V

  • Other colors for signal wires

• Code Setup

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1. Import necessary libraries

2. Include a program header that includes your name, section, assignment/program function

3. Define constants and variables

   1. Be consistent

   2. Do not mix and match camCase or under_scores

   3. Use descriptive names

4. Define void setup()

   1. Initialize pin modes, libraries, etc

5. Define void loop()

   1. Always keep code in the void loop

   2. This is the “main” program

   3. Use helper functions

6. Define helper functions

   1. Don’t Repeat Yourself - DRY

   2. Create reusable, modular code

7. Comment your code

   1. Avoid obvious comments

   2. Comments should help non-coder follow the program’s logic

Working with Pushbuttons

• Pushbutton = momentary switch

• Push button → make connection → current flows from one of the side of the switch to the other side of the switch

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  • Metal bar connects pins A and B

  • Metal bar connects pins C and D

  • Closing switch → connection pints A & B with pins C & D → allows current to pass through switch

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• Floating pins

  • The button state (HIGH or LOW) should only change when you want it to

  • Input pins are sensitive when it comes to detecting signals

  • Floating: without correction state, pin state floats on water, bobbing up and down

    • Bobs between different signal levels

    • Causes unpredictable behavior

    • Example: digital input pin meant to read the state of a button may detect a wireless signal from the environment and incorrectly return a button state of High (1) instead of Low (0)

• Fix floating pins

  • Connect the switch to ground using a very large resistor (10 kΩ). If any signals are detected while the button is not pressed, the large resistance will reduce the signal level to almost zero keeping the state LOW.

• Contact Bounce

  • Normally open contacts - N.O.

    • When they close or open, the thin mental contacts come together and bounce off each other like a spring

    • This happens during the first milliseconds before making a solid connection

  • Occurs because contacts are make from spring-like metals

    • Contacts are designed to open and close quickly

    • Little resistance to movement

  • Arduino has response time of microseconds - will be able to detect and respond to bouncing

  • Debouncing: Add a timing delay of 10ms to wait out the contact bounce period

    • Hardware debouncing: reduce KE using buffer springs and shock absorbers

    • Software debouncing: add time delay or use function to resolve bounce

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Using the RGB LED

• Contains 2 individual LEDs with a common cathode, the longest pin that gets connected to ground

  • R - red

  • G - green

  • B - blue

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• Use Arduino’s digital I/O pints with PWM (marked with ~) to specify RGB colors

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  • To send PWM value from Arduino to LED, use analogWrite function

  • analogWrite(pin, value)

    • analogWrite(redPin, 255) – red on at 100% intensity

    • analogWrite(redPin, 0) – red off (on at 0% intensity)

    • analogWrite(redPin, 127) – red on at 50% intensity

Ultrasonic Sensor (Range Finder)

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  • Vcc - connected to 5V

  • Gnd - Ground

  • Trig - trigger (transmits sonic pulse)

  • Echo - receives the echo pulse

• Trig pin sends a sonic burst → sound wave will reflect off object → create echo wave → echo wave received by echo pin, the receiver → echo pin outputs time (in microseconds) that the sound wave traveled

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  • Object Distance (cm) = speed of sound (cm/μs) * time (μs) /2

    • Speed of Sound (@ 20°C/68 °F) = 343 m/s or 0.034 cm/μs

    • Time = distance / speed (this is the time that it takes the signal to travel from the transmitter to the object and back to the receiver)

      • Use long datatype for the duration, an int datatype for the distance, and float datatype for the speed of sound.

  • Make sure to connect Vcc to 5V and GND to GND

    • Connecting backwards = short circuit

  • Trig and echo can be connected to any digital pin

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• delayMicroseconds(); – delay the operation for specified microseconds

• digitalWrite(); – used to set the trigPin HIGH or LOW

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• pulseIn(echoPin, HIGH); – receive the echo signal and returns soundwave travel time in microseconds.

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Temperature Sensor

• analog input

  • Connects to analog input pins (A0 - A5)

  • analogRead(tempPin) is used to read input from temperature sensor

  • Build int analog to digital converter (ADC) converts analog signal from sensor to digital one

    • Values returned by ADC range is from 0-1023

    • ADC value is converted to voltage value (in mV), which is then converted to temperature value

      • Arduino Uno pins operate on 5V, which results in a resolution of 5000mV/1024 units or 4.9V per unit

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Pulse Width Modulation (PWM)

• PWM: A technique that allows you to simulate an analog signal using digital means

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• analogWrite(): used to send a PWM value from the Arduino to the LED

  • analogWrite(pin, value)

    • Pin - arduino PWm pin

    • Value - integers in range [0, 255]

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  • 2 possible supply voltage values: 5V (HIGH) and 0V (LOW)

  • Analog signals have an infinite number of values within range

    • Arduino simulates analog signals using PWM

    • Instead of varying supply voltage between 0V and 5V (rapidly switching between HIGH and LOW), it uses the average voltage provided by signal

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  • If PWM signal generated at pins 3, 9, 10, 11, there would be 490 cycles per second

  • Duty Cycles

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  • LED brightness with duty cycles of 4%, 20%, 50%, 100%

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Potentiometer

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  • Allows you to change resistance by turning know

  • Signal pin connection to analog ports (A0 - A5)

  • Returns value [0, 1023], corresponding to amount of electricity the analog pin receiver

  • analogRead() reads potentiometer value

  • Connect 5V to terminal 2: turn clockwise to increase (used most often)

• Converting potentiometer values to PWM values

  • Potentiometer: 0-1023

  • PWM: 0-255

  • Linear mapping used

  • map(value, fromMin, fromMax, toMin, toMax)

    • Use linear interpolation to map given value in [fromMin, fromMax] to corresponding value in [toMin, toMax]

    • Must use integer math

    • Fractional components are truncated

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Liquid Crystal Display (LCD)

• Unpolarized light: light that vibrates in multiple directions

• Polarized light: light that vibrates in one direction

• Polaroid filter: blocks one of the two planes of vibration of an electromagnetic wave, polarizing it.

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  • Used to display text

  • When an electric charge is applied to liquid crystal molecules, they untwist, changing their alignment

  • This change in alignment affects if it blocks polarized light or not

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I2C (Inter-Integrated Circuit)

• Better method for connecting LCD to arduino

• LCDs normally require 6 data pins and 2 power pins, which could potentially cause shortage of pins for larger projects

• LCDs with a board on back with 4 pins have an I2C expansion board

  • I2C expansion board reduced number of data pins from 6 to 2 using SDA and SCL pins

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• Use hd44780 library

Temp/Humidity Sensor with LCD

• DHT11 Temperature and Humidity sensor

  • Connects to digital pin 2

  • Use DNT sensor library

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Photoresistor

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  • Photodetector, light detector, CdS, photoconductive cell, LIGHT SENSOR

  • Changes resistance depending on light exposure intensity

    • Light -> low resistance: ∼1 kΩ

    • Dark -> high resistance: ∼ 10 kΩ

• Since arduino analog pins measure change in voltage, to measure photoresistor’s resistance, a 10 kΩ resistor is used to create small current

  • This allows arduino to measure voltage across photoresistor

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• analogRead() used to measure voltage

  • ADC converter will convert voltage to a value in [0, 1023]

  • As amount of light detected increase, value returned increases

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Motor Control

• Electric motors convert electrical energy to mechanical energy

• In a DC motor, a wire with current running through it is passed through a magnetic field → magnetic force produces torque → turns motor

• Commutator reverses current each hald turn to keep torque turning motor in same direction

• Motor acts as inductor

  • Stores energy in magnetic filed

  • Opposes sudden changes in current

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• H-Bridge

  • Controls motor direction

    • To control rotation direction, reverse direction of current flow into motor

    • Speed of motor controlled by PWM

    • H-bridge, a circuit, reverses direction of current flow

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• L298N Motor Driver

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• Motor Dead Zone (Activity 1.2.7.14)

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    • Turn know CW → motor speed increases in forward direction

    • Dead-zone

      • Sufficient voltage needs to be supplied to overcome friction in motor for shaft to turn

      • If voltage is insufficient, buzzing sound will occur

      • To prevent buzzing, PWM value of minimum speed is required to get the motor to turn

        • Use this threshold value as the dead-zone

        • Any motor speed value below threshold results in motor remaining OFF

• Motor Dead Zone (Activity 1.2.7.15)

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• Code

  • If motor has no load, don’t run motor at max speed

    • Keep PWM value below 150

  • Use digitalWrite() to control motor direction

    • digitalWrite(in1, HIGH) - turn motor in forward direction

    • digitalWrite(in1, LOW) - turn motor off

  • Set motor control pins to OUTPUT

    • pinMode(in1, OUTPUT)

  • Set potentiometer to INPUT