SoftBlink1 Arduino Sketch¶
This sketch is used by Exercise: Soft Blink.
Full Source Code¶
The full code is all in one file SoftBlink1.ino.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 | // SoftBlink1 - fades the onboard LED on and off.
//
// Copyright (c) 2016, Garth Zeglin. All rights reserved. Licensed under the
// terms of the BSD 3-clause license as included in LICENSE.
//
// The Arduino UNO we use has an onboard LED on pin 13. This sketch varies the
// visible LED intensity using a form of "pulse width modulation" (PWM)
// implemented in software. The example turns the LED on and off very fast
// using short delays within a loop; the average energy emitted is lower than
// constantly being ON.
//
// The output voltage signal looks something like this as a function of time:
//
// ---- ---- ---- ----
// | | | | | | |
// --- ---- ---- ----
//
// For even dimmer output, the proportion of 'ON' time can be reduced:
//
// -- -- -- --
// | | | | | | |
// --- ------ ------ -----
//
// This sketch also introduces several conventional programming structures.
//
// ================================================================================
// Configure the hardware once after booting up. This runs once after pressing
// reset or powering up the board.
void setup()
{
// Initialize the hardware digital pin 13 as an output. The 'OUTPUT' symbol
// is pre-defined by the Arduino system.
pinMode(LED_BUILTIN, OUTPUT);
}
// ================================================================================
// Define constant values. The following lines defines "pre-processor macros"
// which can be used to replace one text symbol with a value as the first step
// in compiling the code. In general, this a recommended practice for making
// the intent of the code more legible.
// Define the period of the PWM waveform in milliseconds. E.g., the text
// 'PWMPERIOD' will be replaced by the text '10' in the code which follows.
const int PWMPERIOD = 10;
// Define the duration of each fade ramp in millisconds.
const int RAMPPERIOD = 1000;
// Note that constant values can include expressions. The following line
// determines how many discrete steps will be required to complete the ramp in
// approximately the specified time:
const int RAMPSTEPS = RAMPPERIOD/PWMPERIOD;
// ================================================================================
// Run one iteration of the main event loop. The Arduino system will call this
// function over and over forever.
void loop()
{
// Ramp from off to on. The next code line begins a 'for loop' which will
// iterate the block delineated by curly braces, with details as follows:
//
// int i = 0; Declare a new integer variable named 'i' and assign it an initial value of zero.
// i < RAMPSTEPS; This condition determines whether to keep iterating.
// i = i+1 Increment the value of i after the completion of each iteration.
//
// The net effect is that the loop with execute RAMPSTEPS times, with the
// value of i counting up on each iteration: 0, 1, 2, ... On the last
// iteration i will be equal to RAMPSTEPS-1.
for(int i = 0; i < RAMPSTEPS; i = i+1) {
// Declare a new local integer value to hold the duration of time the LED should remain on.
// This uses the highly convenient map() function which remaps a value from one range to another.
// i has values over range (0,RAMPSTEPS) which are remapped to the range (0,PWMPERIOD).
int time_on = map(i, 0, RAMPSTEPS, 0, PWMPERIOD);
// Similarly for the off time. Note that (time_on + time_off) always equals PWMPERIOD.
int time_off = PWMPERIOD - time_on;
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on
delay(time_on); // wait the specified number of milliseconds
digitalWrite(LED_BUILTIN, LOW); // turn the LED off
delay(time_off); // wait the specified number of milliseconds
}
// Ramp from on to off. Note the code is nearly identical; the only
// difference is that the roles of time_on and time_off are switched.
for(int i = 0; i < RAMPSTEPS; i++) {
int time_off = (i * PWMPERIOD) / RAMPSTEPS; // equivalent to map() above
int time_on = PWMPERIOD - time_off;
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on
delay(time_on);
digitalWrite(LED_BUILTIN, LOW); // turn the LED off
delay(time_off);
}
// After this event loop iteration exits, the loop() function will be immediately called again.
}
// ================================================================================
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