LED

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Controlling LEDs with RPi

PCA9685 I2C board

Board and guide

Steps to get it to work

1. Connect VCC to Pi's 3.3v, GND to Ground
2. Connect the SCL to pin 05 (GPIO3) SDA to pin 03 (GPIO2)
3. sudo apt-get install python-smbus i2c-tools
4. Add the following two lines to /etc/modules/ with something like sudo nano:
   i2c-dev
i2c-bcm2708
5. Add the following lines to /boot/config.txt and reboot: (see this for older Pi's)
   device_tree=bcm2708-rpi-b-plus.dtb
device_tree_param=i2c1=on
device_tree_param=spi=on

6. Run sudo i2cdetect -y 1 and you should see something like this:
   
   If everything was setup correctly, you now should be ready to go