PWM Exponential LED Fading on Arduino (or other platforms)

For a project I am working on I needed to dim a LED strip light using the PWM (pulse width modulated) outputs on an Arduino. The most straightforward way to do this would have been to linearly vary the output frequency. Shown below in an Arduino sketch:

// Use pin 9 as the PWM output
const int outputPin = 9;

void setup() {
  // Set the pin as a digital output
  pinMode(outputPin, OUTPUT);
}

void loop() {
  // Fade the brightness from 0 (min) to 255 (max) with 40ms delay per step
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(outputPin, brightness);
    delay(40);
  }
}

However the light outputted by the LED does not scale linearly. If you were to use the very scientific metric of “Perceived Brightness” vs. time for the above sketch it would look something like the below for a linear PWM signal:

brightness_vs_time_linear

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Experiences with Buying Cheap Arduinos and shields on eBay

Recently I’ve started getting interested in electronics and in particular Arduino. Ardunios are a microcontroller boards that you can programme to perform actions. The board I am interested in is the entry level Ardunio Uno. This board has 14 digital inputs/outputs and 6 analogue inputs. The Arduino can be expanded with Shields, these are addon boards that stack on top of the Arduino to offer additional functionality (like ethernet, storage, motors etc.)

Buying genuine Arduinos in Ireland can be costly because they have to be ordered from suppliers in the US or UK/Europe. Often the cost of shipping and customs exceeds the cost of the Arduino itself!

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Donald Crowhurst: The Man Who Sailed Around The World Without Leaving The Atlantic

Donald Crowhurst

I Wrote this essay for a college course on Project Management. The guidelines stated we had to write about a project that failed.


Donald Crowhurst Was a British Businessman and amateur sailor who died while competing in the Sunday Times Golden Globe Race, a race to be the first to sail single headedly non-stop around the world. Faced with mounting financial and technical challenges prior to the start of the race Crowhurst departed from Teignmouth, Devon, on the last day permitted by the rules: 31 October 1968. From the beginning of the race Crowhurst realised that his boat was not suitable for the race and began reporting false positions, in an attempt to appear to circumnavigate the world without actually doing so. Four months into the race Crowhurst’s boat was found drifting in the north Atlantic with no one aboard. Evidence from his logbooks indicates that his race ended in insanity and apparent suicide (Hall and Tomalin 1970).

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