Basic Library

Digital I/O
Analog I/O
Advanced I/O
Time
Math
Trigonometry
Random Numbers
Bits and Bytes
Interrupts
Serial Comm.

Standard Library

Camera
Servo Motor
Stepping Motor
Character LCD
SPI
I2C (Wire)
SD Card
SD (File Operations)
Periodic Operation
Clock (RTC)

Mbed Tips

Overview
Storage
Wi-Fi
TLS (HTTPS)
Audio
Microphone
BLE

Random Number

This library obtains random numbers. True random numbers can be obtained from ESP32 as shown in the sample.

randomSeed

Description
randomSeed() initializes the pseudo-random number generator, causing it to start at an arbitrary point in its random sequence. This sequence, while very long, and random, is always the same.
Syntax
randomSeed(unsigned int seed)
Parameters
seed: A number to generate the seed
Returns
None

random

Description
Obtains the random numbers. Always call the randomSeed function before using this function.
Syntax
long random(long min_num, long max_num)
Parameters
min_num: Lower bound of the random value, inclusive (optional)
max_num: Upper bound of the random value, exclusive (optional)
Returns
A random number (long)

Sample Program

This example outputs a random number between 0 and 99 in 100ms intervals via serial communications.


#include <Arduino.h>
#define INTERVAL 100
    
void setup()
{
    Serial.begin(9600);
    randomSeed(millis());
}
    
void loop()
{
    Serial.println( random(0, 100) );
    delay(INTERVAL);
}

Get a 32-bit true random number.


#include <Arduino.h>
#include <Wire.h>
#define ESP32_I2C_ADDR    0x28
    
void setup() {
    Serial.begin(9600);
    
    Wire.setFrequency(150000);
    Wire.begin();
    
    pinMode(PIN_ESP_EN, OUTPUT);
    pinMode(PIN_ESP_IO0, OUTPUT);
    pinMode(PIN_SW0, INPUT);
    pinMode(PIN_SW1, INPUT);
    
    digitalWrite(PIN_ESP_IO0, HIGH);
    delay(100);
    digitalWrite(PIN_ESP_EN, HIGH);
    delay(1000);
    
}
    
void loop() {
    Wire.beginTransmission(ESP32_I2C_ADDR);
    Wire.write(0);
    Wire.endTransmission();
    
    uint32_t rand;
    Wire.requestFrom(ESP32_I2C_ADDR, 4);
    rand = Wire.read();
    rand <<= 8;
    rand += Wire.read();
    rand <<= 8;
    rand += Wire.read();
    rand <<= 8;
    rand += Wire.read();
    Serial.print(rand, HEX);         // print the character
    Serial.println();
    delay(100);
}