Once you've blinked a few LED's on and off a few times, you might think, what next ? In this tutorial we will look at using a few LED's to blink in a programmable sequence which can look quite dramatic.
The ATmega328's pins are able to source enough current to drive a single LED, but we still need to limit the current to the LED so as not to damage it. The different color LED's available all have different voltage requirements so a simple LED driver circuit will need to be used, which is simply a single resistor which we will calculate further down the article.
Below is a video that shows the process of creating a sequential LED control using three color LED's.
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Simple LED Driver Circuit
The simplest LED driver circuit is a current limiting resistor in series with the LED you are powering up.
To calculate the resistor value we need to know the supply voltage, LED voltage and the LED current required.. In our case we are using a +5V supply.
The Formula we use is Ohm's law, V=IR, which is voltage equals current multiplied by resistance.
As we want to know the resistance, we rearrange the formula to R = V/I, resistance equals voltage divided by current.
The complete formula is:
resistance (R) = (supply voltage - LED voltage)/ LED current
Step 2: LED Resistor Values (Red and Yellow)
The above diagram shows the resistor values and LED colors and what pins need to be connected to the arduino board.
RED and YELLOW LED's
The Red and Yellow LED's both require 2V and 15mA.
So we put those values into the formula:
R = (5V – 2V) / 0.015 A
R = 200 ohm’s
We choose the closest resistor value of 220 Ohm’s. 220 Ohm’s drops the current slightly to 13.6 mA which will still work.
Step 3: LED Resistor Values (Blue LED)
The Blue LED's requires 3.3V and 15mA. So we put those values into the formula:
R = (5V – 3.3V) / 0.015
R = 113 ohm’s
We'll use the closest resistor value of 100 ohms.
Remember the LED can only be wired in one way. The longest pin is the positive (+) and the shortest pin is the negative(-). If it is wired the wrong way it will not operate.
Step 4: Arduino Coding of the LED Sequence
In this tutorial we blink the LEDs on and off in sequence once, then each LED intern blinks 4 quick blinks then the program starts over in a never ending loop.
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