radsim.ino

/*
radsim.ino
Eric Ayars

Simulate pulses from a half-life experiment using an Arduino.

The way I'm doing this is to have a "decayLevel" that decays according to 
the formula for radioactive decay. Then a random number 'event' is chosen,
and if event is less than decayLevel, a decay has occurred.

This SHOULD give me pulses that decrease in frequency in a manner similar
to that of a radiation source. (Yep. It does.)

*/

#include <math.h>       // allow exp() function

#define PULSE 13        // Pulse output pin

int decayLevel;
long time = 0;
long tau = 100000;      // lifetime 
int event;              // random number storage

void setup() {
    randomSeed(analogRead(0));  // read initial seed from an unconnected
                                // analog input
    pinMode(PULSE, OUTPUT);
}

void loop() {
    time = millis();    // how long has it been...
    decayLevel = int(1000*exp(-float(time)/float(tau)));
                        // the above line sets the threshold for decay
    event = random(1100);   // set this 10% higher than max decaylevel
                            // to eliminate "saturation" at start
    if (event < decayLevel) {
        // Decay occurs. Write a pulse.
        digitalWrite(PULSE, HIGH);
        digitalWrite(PULSE, LOW);
    } else {
        // no decay occurs. Write a non-pulse to keep timing consistent.
        digitalWrite(PULSE, LOW);
        digitalWrite(PULSE, LOW);
    }
}