Using Random Numbers with Arduino

This video tutorial talks about using the random() and randomSeed() functions with Arduino.  It is pretty straight forward, but there are some intricacies worth noting.

Creating truly random numbers in Arduino is harder than you might think.  The closest we can get in Arduino, and just about anywhere else, is using pseudo random numbers.  That is, numbers that mimic randomness, but in fact do have a pattern if Want to fast-track your Arduino skills?

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Why are Random Numbers with Arduino All the Same?

The most important thing to understand when using the random() function with Arduino is that it will generate the exact same list of pseudo random numbers every time.

So if you build a slot machine, and the first crank of the handle is a winner, then you can be sure that if you reset the Arduino board and pull the handle again - it will still be a winner the first time.

The easy way to overcome this is using the randomSeed() function.

This function takes a value (an integer for example), and uses the number to alter the random list generated by the random() function.  The number you pass to the randomSeed() function is called a 'seed'.

You might put randomSeed() in the setup, and then use the random() function in the loop.  Something like this:

//this variable will hold a random number generated by the random() function long randomNumber; //Set up - this is where you get things "set-up". It will only run once void setup() { //setup serial communications through the USB Serial.begin(9600); //Let's make it more random randomSeed(42); }//close setup void loop() { //generate a random number randomNumber = random(2,5); //display the random number on the serial monitor Serial.print("The Random Number is = "); Serial.println(randomNumber); }

But there is still an issue - even though the sequence of random numbers is different when using the randomSeed() function - it will still be the same every time the sketch is run.  It is just a different list of pseudo random numbers!

 

One Solution to the Random Problem

So, what to do?  Lucky for us the Arduino reference has a great solution.  Use the analogRead() function to read a value from an unused analog pin.  Since an unused pin that has no reference voltage attached to it is basically 'floating', it will return a "noise" value. This noise value can seed the randomSeed() function to produce differing  sequences of random numbers every time the sketch is run.

 

Below is the sketch from the video using analogRead() and randomSeed() in unison:

/*How to use the random() and randomSeed() function YOU WILL NEED: (3) LEDs (3) 220OHM resistors (1) Jumper Wire (4) Hot cakes CIRCUIT: Connect a resitor to pin 2 and then to a breadboard. Connect the long leg of an LED to the resitor and the short leg to one of the ground rails on the breadboard Repeat this for the other components at pin 3 and 4 Coonect the ground on the breadboard to one of the Arduino GND pins. Created JUL 2014 by Michael James https://programmingelectronics.com/thearduinocourse */ //Declare and initialize LED pin variables int LED_1 = 2; int LED_2 = 3; int LED_3 = 4; //this variable will hold a random number generated by the random() function long randomNumber; //Set up - this is where you get things "set-up". It will only run once void setup() { //setup serial communications through the USB Serial.begin(9600); //Let's print a start messgae to the serial monitor when a new sequence of random numbers starts Serial.println("Starting new Random Number Sequence"); //set the LED pins as outputs pinMode(LED_1, OUTPUT); pinMode(LED_2, OUTPUT); pinMode(LED_3, OUTPUT); //Let's make it more random randomSeed(analogRead(A0)); }//close setup //The loop() runs over and over again void loop() { //generate a random number randomNumber = random(2,5); //display the random number on the serial monitor Serial.print("The Random Number is = "); Serial.println(randomNumber);

Well, hopefully that was random enough for you! If you enjoy this tutorial, I highly recommend checking out our free Arduino Crash Course (You can sign up below).