Connect the fan like this:
The hall effect sensor pin goes to pin 2, or interrupt 0. The LED and 10k resistor needed to be there for this to work. If your fan takes a lot of current, you might need to use an external power source.
Simple Circuit Option:
If the internal pull-up resistor for pin 2 (interrupt 0) is enabled by adding the line:
digitalWrite(2, HIGH);
to setup(), then the hall effect sensor can be connected directly to pin 2 without requiring an external 10k pull-up resistor and LED. The LED is actually only serving as a visual indicator in the original circuit and is not mandatory in for either.
Ze code:
//-----------------------------------------------
volatile byte half_revolutions;
unsigned int rpm;
unsigned long timeold;
void setup() { Serial.begin(9600); attachInterrupt(0, rpm_fun, RISING);
half_revolutions = 0; rpm = 0; timeold = 0; }
void loop() { if (half_revolutions >= 20) { //Update RPM every 20 counts, increase this for better RPM resolution, //decrease for faster update rpm = 30*1000/(millis() - timeold)*half_revolutions; timeold = millis(); half_revolutions = 0; Serial.println(rpm,DEC); } }
void rpm_fun() { half_revolutions++; //Each rotation, this interrupt function is run twice }
//-----------------------------------------------
Plot of RPM over time:
(right click -> "view image" to see the larger picture)
by zitron
Edited by Elimelec Lopez - April 25th 2013
// read RPM
int half_revolutions = 0;
int rpm = 0;
unsigned long lastmillis = 0;
void setup(){ Serial.begin(9600); attachInterrupt(0, rpm_fan, FALLING); }
void loop(){
if (millis() - lastmillis == 1000){ //Uptade every one second, this will be equal to reading frecuency (Hz).
detachInterrupt(0);//Disable interrupt when calculating
rpm = half_revolutions * 60; // Convert frecuency to RPM, note: this works for one interruption per full rotation. For two interrups per full rotation use half_revolutions * 30.
Serial.print("RPM =\t"); //print the word "RPM" and tab. Serial.print(rpm); // print the rpm value. Serial.print("\t Hz=\t"); //print the word "Hz". Serial.println(half_revolutions); //print revolutions per second or Hz. And print new line or enter.
half_revolutions = 0; // Restart the RPM counter lastmillis = millis(); // Uptade lasmillis attachInterrupt(0, rpm_fan, FALLING); //enable interrupt } }
// this code will be executed every time the interrupt 0 (pin2) gets low.
void rpm_fan(){ half_revolutions++; }
http://elimelecsarduinoprojects.blogspot.com/2013/06/measure-rpms-arduino.html