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Topic: reading rpm signal from cpu fan (Read 10 times) previous topic - next topic

tomas

hello
I am using arduino to make an RPM meter to read the pulses off an ordinary intel cpu fan with 3 leads (+,-, rpm signal)
I tried using digitalread() and pulsein() but I get fuzzy results.
anyone knows how to read those signals reliably?

code examples:




void loop()
{
 
 scanvalue=digitalRead(7);
 if (scanvalue!=previous_scan) {pulsecount++; previous_scan=scanvalue;}
   
  if (millis() - previousMillis > interval)
 {
  interval=((millis() - previousMillis)/pulsecount)*50
  previousMillis = millis();    
  pulsecount=0;

  //code blinking code here
  }
}

Benoît ROUSSEAU

Hello Tomas,

That the code you are looking for :

Code: [Select]
/***************************************/
// FAN SPEED Arduino
// Benoît ROUSSEAU juillet 2006
// - Mesure de la vitesse de rotation d'un
// ventillateur de CPU sous interruption.
/***************************************/

// variables et définitions
#define INT_0_PIN  2
#define EXTINT_LEVEL_LOW      0x00      // trigger on low level
#define EXTINT_EDGE_ANY            0x01      // trigger on any edge
#define EXTINT_EDGE_FALLING      0x02      // trigger on falling edge
#define EXTINT_EDGE_RISING      0x03      // trigger on rising edge
#define sbi(PORT,BIT) PORT|=_BV(BIT)   // macro pratique pour mettre un bit x à 1 (Set Bit In)

unsigned int NbTopsFan;
unsigned int MeasuredTopsFan;

/***************************************/
// Fonction appelée à chaque
// déclenchement de l'interruption 0
/***************************************/
SIGNAL(SIG_INTERRUPT0)
{
 NbTopsFan++;
}

/***************************************/
// iniInt0
/***************************************/
// Init. interrupt 0
/****************************************/
void initInt0 (byte config)
{
 sbi(GICR, INT0); //
 sbi(GIFR, INT0); //

 MCUCR &= ~((1<<ISC01) | (1<<ISC00)); // raz
 MCUCR |= config; //
}

/***************************************/
void setup()
{
 pinMode(INT_0_PIN, INPUT);
 Serial.begin(9600);
 initInt0 (EXTINT_EDGE_RISING);
};

void loop ()
{
   NbTopsFan = 0;
   delay (1000);
   MeasuredTopsFan = NbTopsFan;
   Serial.print (MeasuredTopsFan * 60, DEC);
   Serial.print (" rpm");
   Serial.print (13, BYTE);
};


It was test and it work !

You have to connect the "sens output" of the cpu fan to the digital pin #2 with a pull-up resitor >= 10Ko to +5V of the Ardiuno board. This output is a open collector ouput. I don'y test the activatation of the internals pull-ups of the ATmega. I don't remerber if they was activated by default but it work with a externel resistor... Take care of that you can't use another pin, interrupt 0 sense only on the #2 pin.

Remenber to connect the ground power of the fan and the ground power of the Arduino card.

Finally, if every thing is connect, open HyperTerminal serial monitor to see every second the fan speed in rpm.
Cordialement,
Benoît ROUSSEAU

tomas

#2
Jul 23, 2006, 01:13 pm Last Edit: Jul 23, 2006, 01:22 pm by tomas Reason: 1
thanks very much friend , merci mon ami
when the project is done I'll post the how-to

kasperkamperman.com

Do you have a link were the source code is explained ? I'm trying to understand the code. It seems I can't find all the info in the arduino reference. Are there any other resources we're I can find this information ?

Especially the void initInt0() function is hard to understand.

hope you can give me some hints.

Benoît ROUSSEAU

#4
Aug 09, 2006, 06:52 am Last Edit: Aug 09, 2006, 06:57 am by Benoit Reason: 1
Hello,

 Yes I will do it... If you understand french there's explanations here : http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1147164546.

  Else,

  Download the full datasheet of ATmega8 here http://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf take a look at the #66 page "External interrupts".

void initInt0 (byte config)
{
// set bit 6 "External Interrupt Request 0 Enable" in the General Interrupt Control
// Register - GICR

 sbi(GICR, INT0);

// set bit 6 "External Interrupt Flag 0" in the General Interrupt Flag
// Register - GIFR

 sbi(GIFR, INT0);

// set ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
// in the MCU Control Register - MCUCR

 MCUCR &= ~((1<<ISC01) | (1<<ISC00)); // raz
 MCUCR |= config; //
}

Extracts of datasheet

The MCU Control Register contains control bits for interrupt sense control and general
MCU functions.
? Bit 3, 2 - ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The External Interrupt 1 is activated by the external pin INT1 if the SREG I-bit and the
corresponding interrupt mask in the GICR are set. The level and edges on the external
INT1 pin that activate the interrupt are defined in Table 31. The value on the INT1 pin is
sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last
longer than one clock period will generate an interrupt. Shorter pulses are not guaranteed
to generate an interrupt. If low level interrupt is selected, the low level must be held
until the completion of the currently executing instruction to generate an interrupt.

? Bit 1, 0 - ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the
corresponding interrupt mask are set. The level and edges on the external INT0 pin that
activate the interrupt are defined in Table 32. The value on the INT0 pin is sampled
before detecting edges. If edge or toggle interrupt is selected, pulses that last longer
than one clock period will generate an interrupt. Shorter pulses are not guaranteed to
generate an interrupt. If low level interrupt is selected, the low level must be held until
the completion of the currently executing instruction to generate an interrupt.
General Interrupt Control
Register - GICR
? Bit 6 - INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and
ISC00) in the MCU general Control Register (MCUCR) define whether the external
interrupt is activated on rising and/or falling edge of the INT0 pin or level sensed. Activity
on the pin will cause an interrupt request even if INT0 is configured as an output. The
corresponding interrupt of External Interrupt Request 0 is executed from the INT0 Interrupt
Vector.
Table 32. Interrupt 0 Sense Control
ISC01 ISC00 Description
0 0 The low level of INT0 generates an interrupt request.
0 1 Any logical change on INT0 generates an interrupt request.
1 0 The falling edge of INT0 generates an interrupt request.
1 1 The rising edge of INT0 generates an interrupt request.

Cordialement,
Benoît ROUSSEAU

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