This document provides an overview of using Arduinos for hardware hacking and includes instructions for four example projects: 1. An LED sweep circuit that uses digital output pins to light up LEDs in sequence. 2. An analog LED sweep that dims the brightness of trailing LEDs using PWM. 3. A variable speed circuit that uses a potentiometer as a voltage divider to control delay time based on input voltage. 4. A pause button circuit that uses an interrupt pin to pause and resume the LED sweeping pattern when a button is pressed. Safety tips are also provided around using appropriate voltages and ensuring components are oriented correctly.

1. Hardware Hacking
and Arduinos
Howard Mao and Mason Silber

2. Downloading the Arduino IDE
● Go to www.arduino.cc/en/main/software
○ Download whichever software fits your Operating
System
● Linux users: find the "arduino" package in
your distro's repository
● OSX users: make sure to also install USB
FTDI drivers
○ http://www.ftdichip.com/Drivers/VCP.htm

3. What you have in front of you:
● Arduino Duemilanove
● USB Cable
● Breadboard
● Box of jumper wires
● 4 1k-ohm resistors (Brown-Black-Red)
● 1 100k-ohm resistor (Brown-Black-Yellow)
● 1 100k-ohm potentiometer
● 4 Light Emitting Diodes (LEDs)
● 1 push button switch

4. LED
● Light-emitting Diode
● Produces light when current flows through
● Current can only flow one way

5. Rules for LEDs
● Always use inline resistor
● Make sure direction is right (long pin is +)

6. Digital Output
Voltage can be HIGH (+5 V) or LOW (0 V)
pinMode(pin, OUTPUT) sets pin to output
digitalWrite(pin, HIGH) sets voltage high
digitalWrite(pin, LOW) sets voltage low

7. Breadboards
● Red channel for power
● Blue channel for ground
● Slots on horizontal channels all
connected together internally
● Except break in middle of
board
● Bridge two unconnected lines
of breadboard to build your
circuit

8. Basic Arduino Program Structure
void setup()
{
//All initial settings go here
}
void loop()
{
//Runs indefinitely after setup has completed
}

9. Lab 1: LED sweep
● Connect LEDs to Arduino pins 8, 9, 10, 11
● Turn only one on at a time
● Sweep left and then right

10. "Analog Output" : PWM
● Higher voltage gives brighter LED
● Use PWM to approximate lower voltages
● More time spent high (duty cycle) means
higher average voltage
● analogWrite(pin, level) sets PWM duty cycle
● Levels are from 0 to 255 (8 bits)
Duty Cycle = th / T
th
T

11. Lab 2: Analog LED Sweep
● Sweep left and right as before
● But keep a trail of dimmer LEDs behind
● Divide the level of secondary LEDs down by
two after each step

12. Voltage Division
Vout = R2 / (R1 + R2) * Vin

13. Analog Input
● Arduino has an Analog-to-Digital Converter
● Pins A0 - A5
● Use analogRead(pin) to get voltage level
● Levels go from 0 to 1023 (10 bits)

14. Lab 3: Variable Speed
● Use potentiometer (variable resistor) and
resistor to form variable voltage divider
● Connect output of voltage divider to pin A0
● Read output voltage and use it to control
delay time

15. Buttons and Switches
● Two kinds of switches
○ Single Throw - open or closed
○ Double Throw - one branch or another
● Closed switch has 0 resistance
○ Acts as a wire
● Open switch has infinite resistance
○ No current can flow

16. Pull-up Resistors
● Open switch with no voltage driver is an
antenna, not necessarily ground
● Use pull-up resistors when combining single-
throw switches and digital logic

17. Interrupts
● Tell the Arduino that a digital input has
changed
● attachInterrupt(interrupt, function, mode)
sets function to be run on interrupts
● Interrupt 0 -> pin 2, Interrupt 1 -> pin 3
● Modes are CHANGE, RISING, FALLING,
LOW

18. Lab 4: Pause Button
● Connect push button to Arduino pin 2
● Set pin mode to INPUT_PULLUP
● Attach interrupt for pin 2
● When button pressed (switch closed), pause
the sweeping
● When button released (switch open), resume
the sweeping

19. Congratulations! You did it!

20. Some safety rules to remember
● Do not use very high voltages
○ microcontrollers like Arduino use either 5 V or 3.3 V
● Do not short power to ground
● Do not touch small resistor (< 100 Ohm)
after voltage is applied
○ power is inversely proportional to resistance
○ power in resistor is dissipated as heat
○ small resistor + normal voltage = hot! hot! hot!
● Make sure directional components are in
right direction

21. Learning More
● Arduino website (http://arduino.cc) has many
good tutorials and resources

22. The End
Have fun at HackNY