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.

Files at this revision

API Documentation at this revision

Revision 19:46d7ab0ba3e7, committed 2013-10-09

Comitter:
DavidEGrayson
Date:
Wed Oct 09 01:13:49 2013 +0000
Parent:
18:34ba573573df
Child:
20:656bbcb64e3b
Commit message:
Changed the timing so that this library only supports the high-speed strips now.

Changed in this revision

PololuLedStrip.cpp Show annotated file Show diff for this revision Revisions of this file
PololuLedStrip.h Show annotated file Show diff for this revision Revisions of this file
led_strip_write_color.s Show annotated file Show diff for this revision Revisions of this file 
--- a/PololuLedStrip.cpp	Fri Mar 01 05:17:02 2013 +0000
+++ b/PololuLedStrip.cpp	Wed Oct 09 01:13:49 2013 +0000
@@ -2,8 +2,8 @@
 
 bool PololuLedStrip::interruptFriendly = false;
 
-// The three timed delays, in units of half-cycles.
-uint8_t led_strip_write_delays[3];
+// The two timed delays, in units of half-cycles.
+uint8_t led_strip_write_delays[2];
 
 void PololuLedStrip::calculateDelays()
 {
@@ -11,28 +11,26 @@
 
     if (f_mhz <= 48)
     {
-        // The delays below result in 800/1590 ns pulses and a 2500 ns period on the mbed NXP LPC11U24.        
+        // The delays below result in 360/1120 ns pulses and a 1880 ns period on the mbed NXP LPC11U24.        
         led_strip_write_delays[0] = 0;
         led_strip_write_delays[1] = 0;
-        led_strip_write_delays[2] = 5;
     }
     else
     {
         // Try to generally compute what the delays should be for a ide range of clock frequencies.
         
         // The fudge factors below were experimentally chosen so that we would have
-        // ~700/1300 ns pulses and a ~2500 ns period on the mbed NXP LPC1768 (96 MHz Cortex-M3).
+        // ~100/840 ns pulses and a ~1430 ns period on the mbed NXP LPC1768 (96 MHz Cortex-M3).
         // There seem to be some ~100 ns inconsistencies in the timing depending on which example program is
         // running; the most likely explanation is some kind of flash caching that affects the timing.
         // If you ever change these numbers, it is important to check the the subtractions below
-        // will not overflow in the worst case, which is f_mhz = 49.
-        led_strip_write_delays[0] = 700*f_mhz/1000 - 23;
-        led_strip_write_delays[1] = 600*f_mhz/1000 - 18;
-        led_strip_write_delays[2] = 1200*f_mhz/1000 - 33;    
+        // will not overflow in the worst case (smallest possible f_mhz).
+        led_strip_write_delays[0] = 750*f_mhz/1000 - 33;
+        led_strip_write_delays[1] = 550*f_mhz/1000 - 20;    
     }
  
     // Convert from units of cycles to units of half-cycles; it makes the assembly faster.   
-    for(int i = 0; i < 3; i++)
+    for(int i = 0; i < 2; i++)
     {
         led_strip_write_delays[i] <<= 1;
     }

--- a/PololuLedStrip.h	Fri Mar 01 05:17:02 2013 +0000
+++ b/PololuLedStrip.h	Wed Oct 09 01:13:49 2013 +0000
@@ -45,7 +45,7 @@
         To update all the LEDs in the LED strip, count should be equal to or greater than the number of LEDs in the strip.
         If count is less than the number of LEDs in the strip, then some LEDs near the end of the strip will not be updated.
         
-        The colors are sent in series and each color takes about 60 microseconds to send.
+        The colors are sent in series and each color takes about 45 microseconds to send.
         This function disables interrupts temporarily while it is running.
         This function waits for over 10 us at the end before returning to allow the colors to take effect.
         */

--- a/led_strip_write_color.s	Fri Mar 01 05:17:02 2013 +0000
+++ b/led_strip_write_color.s	Wed Oct 09 01:13:49 2013 +0000
@@ -49,29 +49,36 @@
 send_led_strip_bit
     str r3, [r1]       ; Drive the line high.
     
-    delay #0
+    ; It doesn't really matter exactly how long we delay here as long as it is
+    ; less than 540 microseconds.
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
     
     ldr r4, =0x80000000
     tst r6, r4
-    bne delay1
+    bne delay0
     str r3, [r2]       ; If the bit to send it 0, drive the line low.
-delay1
+delay0
 
-    delay #1
+    delay #0
 
     ldr r4, =0x80000000
     tst r6, r4
-    beq delay2
+    beq delay1
     str r3, [r2]       ; If the bit to send is 1, drive the line low.
-delay2
+delay1
     
-    delay #2
+    delay #1
     
     lsls r6, r6, #1           ; Shift color bits.
     subs r7, r7, #1           ; Decrement the loop counter.
     bne send_led_strip_bit    ; Send another bit if we have not reached zero.   
     pop {r4, r5, r6, r7, pc}  ; Otherwise, restore the registers and return.
-    
+    bx lr;
 
 delay_region
     ; The following is 128 nops.