External flashing LED

My first IoT project was to get the on board LED flashing which I achieved here:

Not as easy as IoT

With that accomplished, I now wanted to get an external LED flashing.

I firstly needed to pick a pin on the Adafruit device to control the output on.

I chose the third in from the bottom on the right which is PIN 2.

Next, I needed to work out the maximum output voltage for the Adafruit Feather Huzzah, which turns out to be 3.3 Volts. I also noted the following from the pin output specifications as well:

“be aware the maximum current drawn per pin is 12mA. 6mA recommended”

I also needed to take into account the voltage drop that would occur across the LED, which is around 0.7V. So the voltage for my calculation was now:

3.3V – 0.7V = 2.3V

To work out what resistor I needed to place in the circuit I used the good ole V= IR.

V=IR

R = V/I

R = 2.3 / 0.006

R = 433 ohms

I double checked my logic at:

http://www.anycalculator.com/ohmslaw.htm

I then went through the:

Microsoft Azure IoT Starter Kit w/ Adafruit Feather HUZZAH

I had bought to see what resistors were included. In there I found a 560 ohm resistor. If you need to check your resistor markings like I did, you can use:

https://byjus.com/physics/resistor-colour-codes/

to help discern what you have.

A 560 ohm resistor would means my current would be:

I = V / R

I = 2.3 / 560

I = 4.1 milliamps (well below the 6 milliamp recommendation)

All I needed now was to find the ground for the Adafruit

which turned out to be the fourth pin from the top on the left.

I therefore wired up the output from pin 2 on the Adafruit, through the LED, through the resistor and then to ground, completing the circuit.

Now for the code to make it flash.

#include <Arduino.h>

int LED_Pin = 2;

int status = 1;

void setup(){

pinMode(LED_Pin, OUTPUT);

}

void loop() {

  // put your main code here, to run repeatedly:

if (status) {

digitalWrite(LED_Pin, HIGH);

  } else {

digitalWrite(LED_Pin, LOW);

  }

status = 1-status;

delay (1000);

}

which is basically the same as before, except the LED_pin now is set to 2. The code is at:

https://github.com/directorcia/Azure/blob/master/Iot/huzzah-ext-flash-led.c

Using PlatformIO IDE I uploaded my code to the Adafruit and after a few minutes was greeted by:

Magic eh?

Sure it’s simple but it’s another step along my IoT journey.