In this lesson you will learn how to work with RGB LED’s. RGB LED’s can be used to create not only the primary colors, but also all mixtures of the primary colors. This video shows you how to connect up a Common Cathode RGB LED. This project is a little more complex than the ones we have done in the past, so I include the code down below. While the code is here for your reference, you should not just copy and paste it. In order to really learn, you need to type it in for yourself, and then find and debug your mistakes. If you just copy and paste from me, you will never learn how to troubleshoot.
Stringmsg="What Colour Do You Want?";
// put your setup code here, to run once:
// put your main code here, to run repeatedly:
In these lessons, we are using the Elegoo Arduino kit, which you can purchase HERE.
You have actually learned quite a bit in the first 13 lessons, and now we are ready to bring it all together in an interesting project. In this lesson, we will show you how to build a dimmable LED. You will read values from a potentiometer, and then based on what value you read, you will set the brightness of the LED. This is a really cool little project, and will no doubt get you thinking about bigger and better things. If you want to follow along at home, you can order the Arduino Kit we are using HERE.
In this lesson we will create a dimable LED. We will read an analog voltage from a potentiometer, and use that to set the brightness on an LED. In order to proceed with this lesson, you will need to connect the following circuit:
Note we are using P9_32 as the reference voltage on the voltage divider, we are using P9_34 as the reference ground, and we are using P9_33 as the analog sense pin. We also using P9_14 as the PWM output pin. Note the current limiting resistor in series with the LED is 330 Ohm.
The object of this circuit is to read the value of the potentiometer and then to use that to set the brightness on the LED. We know that the value we read from the potentiometer will be between 0 and 1. We know that what we can control on the PWM pin is the duty cycle of the 3.3 volt signal. We know that when the potentiometer reads 0, we want a 0% duty cycle on the PWM pin, which would have the LED off. This is our first point:
We also know that when we read 1 from the potentiometer, we want to apply a duty cycle of 100%, or have the LED be full bright. This is our second point:
If we created an equation for the line between these two points, we could calculate the duty cycle that should be applied based on the potentiometer reading. The problem with this is the way our eye perceives changes in brightness. We perceive exponential changes, so if we connected the two points with a linear relationship we would see lots of change at the low end of the scale, but as we continued to move the potentiometer, the brightness would appear to saturate. In order to have a nice smooth transition from full dim to full bright as the potentiometer is moved from left to right, we need to fit an exponential curve between the two points above. We want the LED to be off when the pot is full left, and full bright when the pot is fully to the right. We could use the following exponential equation:
Duty Cycle = C^(Analog Read) – B
This should do the trick, but we need to figure out what the constants C and B need to be. We do this by first plugging in the first point (0,0) from above:
0 = C^0 – B
Anything raised to 0 power is 1, so we have:
0= 1 – B
So B = 1. There, we have our first constant. We use this, and our second point to find C.
100 = C^1 – 1
Now we have everything we need to calculate the Duty Cycle from the value we read from the potentiometer. The final equation is:
Duty Cycle = 101^(Analog Read) – 1
Note that this relationship has the desired properties. When we read a 0 from the potentiometer, we apply a Duty Cycle of 0% to the PWM pin, and the LED is off. When we read a 1 from the potentiometer, we apply a Duty Cycle of 100% to the LED and it is full bright. The exponential shape of the curve between these two points ensures that we will perceive a smooth increase in brightness as we turn the potentiometer up. Math works! It would be very hard to do this by trial and error.
We are now ready to begin developing our code. The video lesson explains the code line-by-line, and we are using commands we learned in the last few lessons.
The code works very well, and produces a very smooth transition from fully off to fully bright.
In this lesson we will explore how to use the PWM commands we learned in the last lesson to control the brightness of LEDs in a circuit. (If you do not have a Beaglebone Black yet, you can pick one up HERE.) In order to proceed with this project, you should hook the following circuit up to your Beaglebone Black.
Note that we are using pins “P9_14” and “P9_22” which are good working PWM pins. Note the current limiting resistors are 330 ohm. Always connect the long leg of the LED towards the control voltage.
The video steps you through the code to control the LED brightness.
This lesson shows a simple example of how to blink two LEDs from the GPIO pins on the Beaglebone Black. To get going, you will need to hook up the following circuit. (If you have not ordered your Beaglebone Black, you can get one HERE.)
Note that the Top LED is connected to Pin “P9_12” and the bottom LED is connected to Pin “P9_11”. We are using 330 ohm current limiting resistors.
The video lesson takes you through several examples of how to blink the LED. Watch the video, and do the examples. Then play around on your own and see what you can make the LEDs do.
Making The World a Better Place One High Tech Project at a Time. Enjoy!