David Grayson / PololuLedStrip

This library lets you control the addressable RGB LED strips from Pololu Robotics & Electronics.

Dependents:   WoYaoChengGOng V2-WoYaoChengGOng STM32_MagneticLight tape_Led_Sample ... more

Summary

This is a library for the mbed that allows you to control these addressable RGB LED products from Pololu:

This library is optimized for the SK6812 and WS2812B, so it transmits colors in green-red-blue order.

If you have a WS2811 LED or a high-speed TM1804 LED strip, please note that its red and green channels are swapped relative to the WS2812B, so you will need to swap those channels in your code. You might prefer to use the version of the library from October 2013, which does not require you to swap red and green in your code.

If you need to control the older, low-speed LED strips (items #2540, #2541, and #2542), you will need to use the version of this library from March 2013.

This library allows complete control over the color of an arbitrary number of LED strips with an arbitrary number of LEDs. Each LED can be individually controlled, and LED strips can be chained together.

This library should also work with any other LED strip based on the SK6812, WS281x, or TM1804.

Supported Platforms

This library has been tested on the mbed NXP LPC1768 (Cortex-M3 at 96 MHz), the mbed NXP LPC11U24 (Cortex-M0 at 48 MHz), and the NUCLEO-F303K8 (Cortex-M4 at 72 MHz). It will probably work on many other boards without modification.

This library does not work on chips families such as the STM32F4 where there is a single register for setting and clearing the value of an output pin. The library checks for the GPIO_IP_WITHOUT_BRR preprocessor macro and triggers a compile-time error if that macro is set.

Getting Started

Software

Here are two example programs that show how to use the library:

Import programLedStripRainbow

This is an example program for the PololuLedStrip library. It generates a simple moving rainbow pattern.

Last commit 01 Nov 2017 by David Grayson

Import programLedStripGradient

This is an example program for the PololuLedStrip library. It generates a simple moving gradient pattern.

Last commit 01 Nov 2017 by David Grayson

As a first step, you should compile and upload one of these to the mbed. When the program runs, the mbed should output color data on pin p8 dozens of times per second. The expected signal is documented on the Pololu website. The example programs only send colors for 60 LEDs, but they can easily be changed to send more for a longer strip.

Hardware

The addressable RGB LED strips can be purchased on Pololu's website using the links above.

The LED strip’s data input connector has two pins that should be connected to the Arduino. The LED strip’s ground will need to be connected to one of the mbed’s GND pins, and the LED strip’s signal input line will be need to be connected to one of the Arduino’s I/O lines. Our example programs assume the signal line is connected to p8. These connections can be made using two Male-Female Premium Jumper Wires, with the female ends plugging into the LED strip and the male ends plugged into a breadboard that houses the mbed.

You will also need to connect a suitable power supply to the LED strip using one of the power connectors. The power supply must be at the right voltage and provide enough current to meet the LED strip's requirements.

If everything works properly, you will see a moving pattern of colors on the LED strip.

Timing Details

This library takes about 1.3 ms to update 30 LEDs (1 meter). The LED strips use a high speed one-wire protocol with relatively strict timing requirements, so this library disables interrupts to ensure reliable color transmission. Unfortunately, disabling the interrupts could cause problems in other libraries that uses interrupts.

This library provides an interruptFriendly option that can let it coexist with interrupt-based libraries. When this option is enabled, the library will temporarily enable interrupts after each color is sent, about every 45 microseconds. If you can keep all of your interrupts short enough, then this option should allow this library to work in conjunction with your interrupt-based libraries. However, if you have an interrupt enabled that takes too long, then this interrupt will sometimes cause an extra long low pulse to emitted, which will be interpreted by the LED strip as a reset command. This can cause visible flickering in the LED strip. To turn on the interruptFriendly option, add this line to the beginning of your main() function:

PololuLedStrip::interruptFriendly = true;

Chaining LED Strips together

No special code is required to chain LED strips together. An X-meter LED strip chained to a Y-meter LED strip can be controlled in exactly the same way as a single (X+Y)-meter LED strip.

PololuLedStrip.cpp@10:f1bb84b97788, 2013-03-01 (annotated)

Committer:
DavidEGrayson
Date:
Fri Mar 01 04:15:35 2013 +0000
Revision:
10:f1bb84b97788
Parent:
9:6ffb85d69eaf
Child:
12:b6df8ac053c8
Saved one cycle per bit by shifting the delays to the left in C.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
DavidEGrayson 1:102307d9b701 1 #include "PololuLedStrip.h"
DavidEGrayson 1:102307d9b701 2
DavidEGrayson 1:102307d9b701 3 bool PololuLedStrip::interruptFriendly = false;
DavidEGrayson 1:102307d9b701 4
DavidEGrayson 7:9a088f042ee0 5 uint8_t led_strip_write_delays[3];
DavidEGrayson 4:d3b60bd43811 6
DavidEGrayson 7:9a088f042ee0 7 void PololuLedStrip::calculateDelays()
DavidEGrayson 7:9a088f042ee0 8 {
DavidEGrayson 8:1578776ceac5 9 // Get the clock frequency in MHz.
DavidEGrayson 8:1578776ceac5 10 int f_mhz = SystemCoreClock / 1000000;
DavidEGrayson 8:1578776ceac5 11
DavidEGrayson 8:1578776ceac5 12 // Arrange for a 700 nanosecond delay between the rise time and the fall time for a 0 bit.
DavidEGrayson 10:f1bb84b97788 13 led_strip_write_delays[0] = 700*f_mhz/1000 - 32;
DavidEGrayson 8:1578776ceac5 14
DavidEGrayson 8:1578776ceac5 15 // Arrange for a 600 nanosecond delay between the fall time for a 0 bit and the fall time for a 1 bit.
DavidEGrayson 8:1578776ceac5 16 // This means the pulses representing a 1 will be 700+600 = 1300 nanoseconds.
DavidEGrayson 8:1578776ceac5 17 led_strip_write_delays[1] = 600*f_mhz/1000 - 19;
DavidEGrayson 8:1578776ceac5 18
DavidEGrayson 8:1578776ceac5 19 // Arrange for a 1200 nanosecond delay between the fall time for a 1 bit and rise time of the next bit.
DavidEGrayson 8:1578776ceac5 20 // This means the period of the signal will be 2500 nanoseconds.
DavidEGrayson 8:1578776ceac5 21 led_strip_write_delays[2] = 1200*f_mhz/1000 - 24;
DavidEGrayson 10:f1bb84b97788 22
DavidEGrayson 10:f1bb84b97788 23 led_strip_write_delays[0] <<= 1;
DavidEGrayson 10:f1bb84b97788 24 led_strip_write_delays[1] <<= 1;
DavidEGrayson 10:f1bb84b97788 25 led_strip_write_delays[2] <<= 1;
DavidEGrayson 7:9a088f042ee0 26 }
DavidEGrayson 6:9d0530b7dae2 27
DavidEGrayson 1:102307d9b701 28 PololuLedStrip::PololuLedStrip(PinName pinName)
DavidEGrayson 1:102307d9b701 29 {
DavidEGrayson 1:102307d9b701 30 gpio_init(&gpio, pinName, PIN_OUTPUT);
DavidEGrayson 1:102307d9b701 31 }
DavidEGrayson 1:102307d9b701 32
DavidEGrayson 1:102307d9b701 33 void PololuLedStrip::write(rgb_color * colors, unsigned int count)
DavidEGrayson 1:102307d9b701 34 {
DavidEGrayson 8:1578776ceac5 35 calculateDelays();
DavidEGrayson 8:1578776ceac5 36
DavidEGrayson 1:102307d9b701 37 __disable_irq(); // Disable interrupts temporarily because we don't want our pulse timing to be messed up.
DavidEGrayson 7:9a088f042ee0 38
DavidEGrayson 1:102307d9b701 39 while(count--)
DavidEGrayson 1:102307d9b701 40 {
DavidEGrayson 9:6ffb85d69eaf 41 led_strip_write_color(colors, gpio.reg_set, gpio.reg_clr, gpio.mask);
DavidEGrayson 9:6ffb85d69eaf 42 colors++;
DavidEGrayson 9:6ffb85d69eaf 43
DavidEGrayson 1:102307d9b701 44 if (interruptFriendly)
DavidEGrayson 1:102307d9b701 45 {
DavidEGrayson 1:102307d9b701 46 __enable_irq();
DavidEGrayson 1:102307d9b701 47 __nop();
DavidEGrayson 1:102307d9b701 48 __nop();
DavidEGrayson 1:102307d9b701 49 __nop();
DavidEGrayson 1:102307d9b701 50 __disable_irq();
DavidEGrayson 1:102307d9b701 51 }
DavidEGrayson 1:102307d9b701 52 }
DavidEGrayson 1:102307d9b701 53
DavidEGrayson 1:102307d9b701 54 __enable_irq(); // Re-enable interrupts now that we are done.
DavidEGrayson 1:102307d9b701 55 wait_us(24); // Hold the line low for 24 microseconds to send the reset signal.
DavidEGrayson 9:6ffb85d69eaf 56
DavidEGrayson 9:6ffb85d69eaf 57 //*(gpio.reg_set) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 58 //*(gpio.reg_clr) = gpio.mask;
DavidEGrayson 9:6ffb85d69eaf 59
DavidEGrayson 1:102307d9b701 60 }