Become a subscriber (Free)

Join 29,000 other subscribers to receive subscriber sale discounts and other free resources.
:
:
Don't worry -- your e-mail address is totally secure. I promise to use it only to send you MicroZine.

How to drive an rgb led using three microcontroller pins.

The RGB LED contains three LEDs encased in one shell: Red, Green and Blue (some contain an extra blue led - as blue LEDs generate less output intensity (candela) per mA). It looks like a single white led except that it has four leads - one for the common ground connection and one for each led.

This project shows you how to produce PWM output without using the internal PWM hardware modules i.e. a software PWM method.

pwm rgb led using microcontroller.

Basic operation

The average current through each of the LEDs determines it's light output i.e. its contribution to the total output color. So by controlling the average current through each LED you can create almost any other color.  

Specification

RGB LED Output colors Red, Green, Blue

RGB LED driver project details.

RGB LED Project
Compiler Mikroelectronika MikroC Compiler Free!
Target 16F877A (retargetable to other PICs that have an 3 output pins!).
Software level Medium.
Software notes Interrupt driven 3 output PWM.
Hardware level Easy.
Hardware notes No special notes
Project version 1.01
Project files Enter your details to get the Download Link
and get the microcontroller newsletter:

Headline


(Your email is safe it will never be sold or rented).
You will get All the C source code and hex file.

Note: Check your email for the project code download link.

You can program the PIC in circuit through the ICSP connector.

Diffuser

By varying the current through each led you can create almost any other color but at close range you only see the individual colors of each LED.

To see the 'merged' color view it from a distance or put a diffuser over it. I used a small piece of baking paper - which is transparent enough to let the light through and opaque enough to diffuse the light from the three LEDs. In a proper design you would use a diffused LED (roughed up!).

It all depends on what you want to do as the light output is reduced when using a diffused LED so you may want to put the RGB LED in a housing that does the diffusing e.g. a semi-transparent plastic housing, in which case you would use a non-diffused LED.

Note: Other projects in the web show the output without a diffuser I think the camera settings merge the light acting as a diffuser (they do - using a digital camera gives the same results i.e. It's not what your eye sees on the bench).

If you make a sign board using these LEDs you won't need a diffuser as your eye will not be able to distinguish the individual LEDs (if it's far enough away - it's exactly the same as a TV pixel).

How it works.

This project uses pulse width modulation to drive each of the leds in the RGB led. By changing the duty cycle of each PWM signal you can control the average current flowing through each led creating any color you want. The limit is set by the resolution of the PWM (set at 256 steps per channel).

The project relies on persistence of vision to make it appear that the led is continuously driven (the PWM signals must be repeated quickly enough so that you do not see any flicker) at a rate greater than 50Hz (approx). Too slow and you begin to see the led flickering.

PWM Software

PIC micros only have one built in PWM module so you need to create three pulse width modulators in software.

This is fairly easy to do using one of the timers in the PIC micro and all that's needed is an 8 bit timer for an output resolution of 1/256.

Note: It's fairly difficult to make it work at 4MHz (it probably can be done in assembler or with more effort in 'C'). So I chose to use a 20MHz crystal just to make it easier.

Heart beat timer

This project uses timer 0 to create a heart beat timer that generates a regular interrupt. The pwm timer tick routine called here controls the PWM operation.

Note: You can use any timer to generate the heartbeat.

Non PWM use

The other way to use a tri-color LED is without using PWM and treat each led line as fully on or off.

Using it in this way you get six color outputs: Red, Green, Blue, Magenta, Cyan and Yellow - without complex PWM control.

Hardware

The hardware is simple with only three wires needed to drive the rgb led.

RGB LED circuit
(Click diagram to open a pdf).

rgb led hardware circuit


RGB LED Software operation

The source code consists of the following files:

RGB LED 'C' Files

  • 16F877A_rgb-led.c
  • pwm.c

RGB LED Header files

  • pwm.h
  • bit.h
  • types.h

RGB LED: pwm.c, pwm.h, types.h

pwm.h defines the prototypes for use in other files.

pwm.c defines a simple pulse width modulator - simplified in that each output uses the same time base. Two user access functions let you initialize the port and set the duty cycle:

  • _pwm_Init( U8 *usePORT, U8 _p1, U8 _p2, U8 _p3 )
  • _pwm_Duty( U8 chan, U8 d )

Note that U8 is defined in types.h as a typedef so and is a short hand for an unsigned short (usually of 8 bits) hence Unsigned 8bit.

Channels are selected in _pwm_Duty from 0 to 2.

RGB LED: PWM interrupt

The main control for the PWM is _pwm_timer_tick(void) which must be called regularly from a timer interrupt. This calls the local file scope function action which then calls chan_action that does the PWM output. Note that a shadow register is used here to ensure the outputs are set correctly.

You would need to integrate the shadow register with other code if other code accesses the same port.

The resolution of the PWM is 256 bits and at each call to _pwm_timer_tick(void) each pwm channel is updated.

RGB LED : 16F877A_rgb-led.c

This function contains main which initializes the PWM on port C and enters an infinite loop.

The random number generator qrn seems more random than the built in one and it uses less memory. It is used in random_start to set a random duty cycle value for each channel and a random sweep direction.

In the infinite loop each channel is swept up and down using the current values from the arrays duty[] and dir[]. This produces a random color pulsating light output.

So that a new random sequence is started after a count of 300 cycles a new random sequence is started so you don't see the same thing over and over.

New! Comments

Have your say about what you just read! Leave me a comment in the box below.



Claim Your: Useful

"Arduino Software Guide"

   Right Now...




Jump from RGB led page 
to Best Microcontroller Projects Home Page.


Privacy Policy | Contact | About Me

Site Map | Terms of Use



Visit our Facebook Page:

   Click Here



Sign up for MicroZine
''The'' Microcontroller Newsletter

Enter your first Name and primary email address in the form below:


And receive absolutely FREE a full project for:

"Measuring Analogue Voltages
Without An ADC"

(Using only one pin).

Instant Download:
You Can
Get It Right Now

Warning: This project could be  Removed 
at any time.  

It will  NOT be 
available indefinitely SO
To avoid 
disappointment  get it:

Now



:
:
Don't worry -- your e-mail address is totally secure. I promise to use it only to send you MicroZine
Remember this is a project with full description and fully debugged C Source code - and it's not available from the main website.

You can only get it through this newsletter.

To get exclusive access Enter your first name Name and primary email address Now in the form above.:



But wait !

There's more...

You'll receive more
free and exclusive reports as well as site information and site product updates


Scroll up to the form above and sign up NOW. Don't forget it's FREE and if you don't like it, you can unsubscribe at any time.

Click Here Now to use the form above to get your Valuable information absolutely free.



Readers Comments

"I wanted to thank
you so so so much
for all the information
you have provided in
your site it's

SUPERB and FANTASTIC."

- Ranish Pottath

"This site really is
the best and my favorite.
I find here many useful
projects and tips."

- Milan

bursach<at>gmail.com<

"Awesome site,
very, very easy and nice
to navigate!"


- Matt
matt_tr<at>
wolf359.cjb.net


Learn Microcontrollers

"Interested in
Microcontrollers?"

Sign up for The
Free 7 day guide:

FREE GUIDE : CLICK HERE


"I am a newbie to PIC
and I wanted to say
 how great your
site has been for me."


- Dave

de_scott<at>bellsouth.net

"Your site is a great
and perfect work.
congratulations."


- Suresh

integratredinfosys<at>
yahoo.com

"I couldn't find the correct
words to define
yourweb site.

Very useful, uncovered,
honest and clear.

Thanks so much for
your time and works.
Regards."


- Anon

Recent Articles

  1. How to use the DHT22 (or DHT11) with an Arduino; full code and description. Also including a comparison of the DHT11 vs DHT22.

    The Essential Guide to the DHT22/11 humidity sensor including a library code guide for the Arduino. Learn how to determine Humidity, Dew point and Heat Index.

    Read more

  2. How to Use the MAX7219 to drive an 8x8 LED display Matrix on the Arduino.

    The Essential Guide to the MAX7219; What it is and how you can easily use one in any of your projects.

    Read more

  3. How to use a DS18B20 (single or multiple on one wire) for temperature measurement using the Arduino Uno.

    How to Easily Use the DS18B20 Maxim One-Wire thermometer with Arduino example code showing external or parasitic power modes.

    Read more