The document compares the Raspberry Pi, Arduino Uno, and a cheap Dell PC for software development and interfacing with hardware. It finds that the Raspberry Pi provides more capabilities than the Arduino for a lower cost than the Dell PC, including options to run Linux, connect to displays and networks, and access GPIO pins to interface with electronics. The remainder of the document demonstrates writing Ruby code on the Raspberry Pi to control LEDs connected to its GPIO pins.

1. Raspberry Pi
Frank Carver
frankcarver.me
raspberryalphaomega.org.uk

4. • ARM1176 CPU @700MHz
• Broadcom BCM2835 chipset & GPU
• 512MB* RAM
• USB, Ethernet, 1080p HDMI, audio
• 8 GPIO pins + UART, SPI, 12C
• Storage on SD/SDHC Card
• Linux, RiscOS etc. or “bare metal”
• About £25

5. Arduino Uno

6. • ATmega328 CPU @16MHz
• No GPU
• 32K Flash, 2K SRAM, 1K EEPROM
• USB, no network or video
• 14 GPIO pins, 6 analogue inputs
• No storage
• “Bare metal” cross-compile only
• About £18

7. Cheap Dell PC

8. • Intel CPU @2.8GHz
• Intel HD GPU
• 2GB RAM
• USB,Ethernet,SATA,HDMI,Wireless,…
• No IO pins
• 500GB hard drive, DVD
• Windows, Linux, etc.
• About £300

10. Software Development
Bare Metal Linux
• Assembler • Pretty much anything
• Cross-compiled C/C+ • Python
+ etc. • Ruby
• Hand-built languages • Java
• perl
• PHP
• bash
• …

11. So let’s do some Ruby

12. So let’s do some Ruby
Step 1: installation

13. So let’s do some Ruby
Step 1: installation
• sudo apt-get install ruby1.9.3
That wasn’t so hard 

14. Ruby talks to hardware
File.open('/sys/class/gpio/export', 'w') { |file| file.write("17") }
File.open('/sys/class/gpio/gpio17/direction', 'w') { |file| file.write("out") }
File.open('/sys/class/gpio/export', 'w') { |file| file.write("27") }
File.open('/sys/class/gpio/gpio27/direction', 'w') { |file| file.write("out") }
File.open('/sys/class/gpio/export', 'w') { |file| file.write("22") }
File.open('/sys/class/gpio/gpio22/direction', 'w') { |file| file.write("out") }
begin
while true do
for r in 0..1
File.open('/sys/class/gpio/gpio17/value', 'w') { |file| file.write("#{r}") }
for g in 0..1
File.open('/sys/class/gpio/gpio27/value', 'w') { |file| file.write("#{g}") }
for b in 0..1
File.open('/sys/class/gpio/gpio22/value', 'w') { |file| file.write("#{b}") }
sleep 1
end
end
end
end
rescue SignalException
File.open('/sys/class/gpio/gpio17/value', 'w') { |file| file.write("0") }
File.open('/sys/class/gpio/gpio27/value', 'w') { |file| file.write("0") }
File.open('/sys/class/gpio/gpio22/value', 'w') { |file| file.write("0") }
end

15. A nicer way
require "pi_piper"
pin_r = PiPiper::Pin.new(:pin => 17, :direction => :out)
pin_g = PiPiper::Pin.new(:pin => 27, :direction => :out)
pin_b = PiPiper::Pin.new(:pin => 22, :direction => :out)
begin
while true do
for r in 0..1
if r==1 ; pin_r.on else pin_r.off end
for g in 0..1
if g==1 ; pin_g.on else pin_g.off end
for b in 0..1
if b==1 ; pin_b.on else pin_b.off end
sleep 1
end
end
end
end
rescue SignalException
pin_r.off
pin_g.off
pin_b.off
end

16. Another way
require "wiringpi"
io = WiringPi::GPIO.new(WPI_MODE_GPIO)
begin
while true do
for r in 0..1
io.write(17,r)
for g in 0..1
io.write(27,g)
for b in 0..1
io.write(22,b)
sleep 1
end
end
end
end
rescue SignalException
io.write(17,0)
io.write(27,0)
io.write(22,0)
end

17. Input
require 'pi_piper'
include PiPiper
watch :pin => 23 do
puts "Pin changed from #{last_value} to #{value}"
end
#Or
after :pin => 23, :goes => :high do
puts "Button pressed"
end
PiPiper.wait

18. So what makes it special?

21. Raspberry Pi
is the gateway drug
to microelectronics

23. More Fun – Ruby USB
• wget http://sourceforge.net/projects/libusb/files/libusb-1.0/libusb-
1.0.9/libusb-1.0.9.tar.bz2
• tar xjf libusb-1.0.9.tar.bz2
• cd libusb-1.0.9
• ./configure
• make
• sudo make install
• sudo apt-get install libusb-1.0-0-dev
• sudo gem install libusb