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Interfacing the Raspberry Pi to the WorldUp close and personal with P1 (and P5!) @OmerK | OSHCAMP 2012 | 15 Sep 2012

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omer.kilic.name

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Agenda● Mechanical Details● Electrical Details● Software Details● Tips for headless operation● Questions

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Mechanical● Standard 100mil (2.54mm) spacing – P1 → 2x13 way – P5 → 2x4 way

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M/F Jumper Cables

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M/F Jumper Cables

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IDC CableRe-use old floppy cables!

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http://www.raspberrypi.org/archives/1404

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“Breakout” boards Pi Cobbler from Adafruit

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Slice of Pi from Ciseco Pi Plate from AdafruitMore at: http://elinux.org/RPi_Expansion_Boards

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Electrical● P1 ● Power ● 3.3V (max I: ~50mA) ● 5V (max I: Power Supply - 700mA) ● 17 GPIO Pins, multiplexed with: ● UART ● I2C ● SPI ● PWM● P5 ● 4 extra GPIO pins ● Power● More signals broken out to S2 and S5 (Camera and flat panel connectors) ● Fiddly!http://elinux.org/RPi_Low-level_peripherals

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Revision 2 – Changes● Fuses protecting the USB outputs have been removed – Power the board via back-feeding hub● JTAG on P1● I2C peripherals swapped● P5 – New header: 4 more GPIO + Power● P6 – Reset Jumper● Mounting holes!!!!!!!!!!!! http://www.raspberrypi.org/archives/1929

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Revision 2

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Power (5V)

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Electrical 3.3V!

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3.3V

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http://www.flickr.com/photos/56601859@N00/3064468115

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Use protection● Level Shifting – Logic buffers (74HCT242) – Birectional translators (TXB0108) – Discrete shifters (FETs + Rs)● Current limiting R

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Recommended Distro Occidentalis by Adafruithttp://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/overview

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Software● Peripherals are memory mapped – Access via /dev/mem ● Faster, needs root, hacky, dangerous! – Use kernel modules/sysfs ● /sys/class/gpio/gpioX/value etc. ● Slower, doesnt need root, easier, (relatively) safer

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Software – GPIO● /sys/class/gpio/ (export|direction|value|interrupt|unexport)● Example: – echo 17 > /sys/class/gpio/export – echo “out” > /sys/class/gpio/gpio17/direction – echo “1” > /sys/class/gpio/gpio17/value● Interrupt support – Use poll() on /value

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Software – I2C● /dev/i2c-0 and /dev/i2c-1● Install the i2c-utils package – i2cdetect, i2cdump, i2cget, i2cset● Support for kernel hardware modules: – echo ds1307 0x68 > /sys/class/i2c-adapter/i2c- 0/new_device● i2c-dev details: – http://kernel.org/doc/Documentation/i2c/dev-interface

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Software – SPI● /dev/spidev0.0 and /dev/spidev0.1 – Chip select pins● Support for kernel hardware modules: – Need to rebuild kernel!● spidev details: – http://kernel.org/doc/Documentation/spi/spidev

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Software – PWM● No kernel module (or libgpio) support, memory mapped voodoo necessary.● WiringPi example: – pinMode(1, PWM_OUTPUT); – PwmWrite(500);

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Libraries● Python – Quick2wire, Rpi.GPIO● C – WiringPi, pihwm● Bindings also available for Java(!), Ruby, Erlang

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Tips for headless operation● Use 240/16 (CPU/GPU) RAM split – No need for graphical stuff● Setup avahi/zeroconf – No need to remember IP address ● ssh raspberrypi.local● Setup mosh – Great for intermittent networking

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Questions?