Been working on a data logging application lately with the intentions of recording my biking sessions and displaying them on a mapping API. The general idea is to use the Hall sensor common in many RPM applications to record revolutions to the EEPROM onboard the Arduino.

I’m having a few issues getting the readings I need, namely the revolutions are not counting with any consistency. I think the issue is with the way Arduino loops through the script. Below is the first iteration of the code I’ve written.

NOTE: Script updated August 31, with Blalor’s suggestions. The RPM reading now works with a high rate of speed.

int pinHall = 2; //Hall Sensor
int pinLed = 13; //Indicator LED
int time = 10000; //EEPROM Write Interval
volatile int rpm = 0; //RPM Counter
 
void setup()
{
    pinMode(pinHall, INPUT);
    pinMode(pinLed, OUTPUT);
 
    Serial.begin(9600);
}
 
void loop()
{
    //Write to EEPROM at specified interval
    if ((millis() % time) == 0)
        writeEEPROM();
 
    //If Hall Sensor triggered then init the test
    attachInterrupt(1, incrementRPM, FALLING);
}
 
void incrementRPM()
{
        rpm++;
        digitalWrite(pinLed, HIGH);
 
        Serial.print("RPM: ");
        Serial.println(rpm);
}
 
void writeEEPROM()
{
    noInterrupts();
    Serial.print("EEPROM: ");
    Serial.println(rpm);
    rpm = 0;
    interrupts();
}

It appears to me like the checkReading() method isn’t firing with any consistency and therefore I’m not incrementing rpm properly. The writeEEPROM() method is firing on target, however I worry that the writing process may be delaying the rpm count.

Below is a Fritzing illustration of the circuit I’ve wired up:

Setup of the Data Logger

Suggestions? I’m open to any hints someone might have on how to structure this a little differently.