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RGB LED Driver

This software can be used to drive an analog RGB LED strip using a raspberry pi and Adafruit's 16-channel 12-bit PWM/Servo Driver - PCA9685:

The Circuit

Here's the basic idea:

  • Hook up the pi to the PCA9685 breakout board using the I2C connections.
  • Connect the pi's 3.3V output to VCC on the PCA9685 breakout board. Leave V+ floating.
  • Follow this tutorial for the RGB LED strips: http://learn.adafruit.com/rgb-led-strips/usage
    • I used N-channel MOSFETs - three of them, one for each channel
    • Connect the +12V from the LED strip to an external power supply (do NOT use your pi for this!)
    • Connect the ground side of the power supply to the pi ground
    • Instead of using the PWM outputs from the arduino, we'll use the PWM outputs from the PCA9685.
    • Connect up the PWM output 0 to the MOSFET with the red wire from the LED strip. Output 1 goes to green, output 2 goes to blue.

Breadboard image

Dependencies

Usage

This program is designed to be included as a python module, but also has some command line options. It, or any python code importing it, must be run as root (sudo), because of the I2C interface.

CLI Options

  • -c [hex color] - Sets the led strip to the color specified.
  • -t - Runs a test of a couple things. Use as a demo.
  • -o - Turn the led strip off after other actions.

As a module

from rgbDriver import RGBDriver
rgb_driver = RGBDriver()

Methods in the module use tuples to describe rgb colors: (red_value, green_value, blue_value). Each color value can range between 0 and 4095, due to the PWM driver's 12 bit resolution. The convert_eight_to_twelve_bit() method can convert a standard 0 to 255 color value to this scale.

To describe a color you can use the string representation of a hex color code and the method hex_to_rgb() to convert it or set_hex_color() and to_hex_color() to use it directly.

The driver keeps a property current_color that stores the led strip's current color (in theory). This is used internally to smoothly transition from one color to another.

Two types of color setting methods exist. to_... will transition a color change over a set time. The last argument of any to_... method is that transition time in milliseconds (default 300ms). set_... will set a color immediately.

Currently supported methods are:

  • to_rgb(rgb, fade=DEFAULT), set_rgb(rgb)
  • to_rand(r_range=(0, 4095), g_range=(0, 4095), b_range=(0, 4095), fade=DEFAULT), set_rand(r_range=(0, 4095), g_range=(0, 4095), b_range=(0, 4095))
  • to_hex_color(color, fade=DEFAULT), set_hex_color(color)

TODO

  • I've got a basic single color led strip and an extra N-channel MOSFET that I want to control.
  • Set current_color var after setting up pwm.

About

Used to drive an analog RGB LED Strip using a Raspberry Pi and Adafruit's 16-Channel 12-bit PWM/Servo Driver.

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