reading rpm signal from cpu fan

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.

Thank you for the explanation. I can understand a little bit French, but I have viewed the link in French thru Babelfish. Do I understand it right that you use the assembly code from the Atmel processor ? Is this because of speed issues or is this the only way ( I'm a beginner ) to do this in Aduino ?

Why do you define so much variables ( especially in the "French post" ), it seems to my that you don't use all those variables.

Do you have some good resources (links, books) we're you can learn programming the Atmel processor ? Or is reading the whole datasheet the best option ?

Hello Kapser,

Long life to BabelFish !

Do I understand it right that you use the assembly code from the Atmel processor ?

  • there no assembly code in this program, just use of some internal function of the ATmega8. The MCUCR, GIFR, ... are just internals registers of the microcontroler and are delaclared in the C library.

Is this because of speed issues or is this the only way ( I'm a beginner ) to do this in Aduino ?

  • nothing about speed, just the only way.

Do you have some good resources (links, books) we're you can learn programming the Atmel processor ? Or is reading the whole datasheet the best option ?

  • Oh ! The bible is the whole datasheet ! Don't read it at once. Look at the index table and just read what is supose to interest you. Take a piece of paper near you to take some notes and simulate by hand on the paper.

  • read the .c and .h of the arduino library is another way of understand and take some ideas.

Thank you for your usefull tips! Sometimes its hard to find a good starting point to learn something. Your example posts and explanation posts are excellent. Very inspirational to see some examples that go deeper into possibility's of Arduino. A blinking led is nice, but sometimes you want more of course. Nice to see that this is actually possible.

Well, I'll have to start reading then :slight_smile:

Kasper

I've tried your code Benoit on 0009 and it get the error:

In function 'void initInt0(byte)':
error: 'GICR' was not declared in this scop

Has the way interrupts changed since this code was written?

You should be able to use a simple call to attachInterrupt (see: http://www.arduino.cc/en/Reference/AttachInterrupt), instead of dealing with the registers directly. In this case, the problem is that the code was written for the ATmega8 and you're probably compiling it for the ATmega168 on which the register names have changed. This is exactly the sort of reason we created the attachInterrupt() function - so you're not reliant on the low-level details of the particular microcontroller.

Ok I still can't get this to work on a Diecimila with 0009. Am I calling the interrupt correctly?

volatile int NbTopsFan = 0;
int hallsensor = 3;

void rpm()
{
++NbTopsFan;
}

/***************************************/
void setup()
{
pinMode(hallsensor, INPUT);
Serial.begin(9600);
attachInterrupt(1, rpm, CHANGE);
};

void loop ()
{
NbTopsFan = 0;

delay (1000);
NbTopsFan = NbTopsFan / 2;
Serial.print (" ");
Serial.print (NbTopsFan, DEC);
Serial.print (" rpm");
Serial.print (13, BYTE);

};

Just to add: I have an external 12V powering the PC fan with the Yellow lead (hall effect sensor) going to pin 3. When I open up the serial monitor I get 60 or 61 rpm, even when the fan is full out going (real rpm is somewhere around 7200) or when it's stopped.

Thanks

**exit: had the wrong pin in my wiring explanation

I wrote this a while ago:

http://www.arduino.cc/playground/Main/ReadingRPM

Hope it helps,
-Z-

Thanks I finally got it working ;D

I was missing the 10k resistor and I used the following as code:

volatile byte NbTopsFan;
int hallsensor = 2;

void rpm()
{
NbTopsFan++;
}

/***************************************/
void setup()
{
// pinMode(hallsensor, INPUT);
Serial.begin(9600);
attachInterrupt(0, rpm, RISING);
};

void loop ()
{
NbTopsFan = 0;

delay (1000);
NbTopsFan = NbTopsFan * 30;
Serial.print (" ");
Serial.print (NbTopsFan, DEC);
Serial.print (" rpm");

};

It was a mix of yours and a mix of Benoit's, at least it works, now to get my character LCD to work. On a side note I couldn't get yours to work, in the terminal I would get random numbers regardless if my fan was running or not.

If I am correct, these fans are brushless but using only 2 wires (+5v and ground). Would reading rpm also be possible with a 3 wire brushless motor?

These pc fans have 3 wires, red (12V+), black(GND) and yellow or green (sensor wire). We're taking advantage of the third wire to read the rotations (2 signals per rotation on the yellow wire).

Take a look at the picture that zitron has on the link he posted, it has a 3 wire fan wired up to the arduino.

I don't know of a way to measure the rpm of a 2 wire fan, I don't think you could do it with just the two wires as they do not give any info on rotation or anything else.

IC, but brushless motors work very differently then the motor used in fans: Brushless DC electric motor - Wikipedia

Anyone that can say if it would be possible to measure rpm for brushless motors as described in the link above (using 3 wires)?

From the wiki article:

Consumer devices such as computer hard drives, CD/DVD players, and PC cooling fans use BLDC motors almost exclusively.

The picture they have of the coils is from a PC fan as well.

The third wire I was using was from the hall effect sensor to measure rpm (used in brushless motors to control 'firing'). It sends a pulse twice every rotation on the third wire.

Ok, point taken, but I want to use it with motors used in model aircraft and those motors don't use 1 wire for sensor. All 3 wires are used to turn the motor.

Ok, point taken, but I want to use it with motors used in model aircraft and those motors don't use 1 wire for sensor. All 3 wires are used to turn the motor.

Ha I'm trying to do the same thing. The model airplane motors are synchronous, so the motor controller must know the RPM of the motor through the three wires. It should be possible to find the RPM by checking the pulses on the wires, since that's what controls the motor speed. Wouldn't it be easier to check the RPM with a photo interrupter or a small magnet on the shaft and a hall effect switch?

-Z-

I have been thinking about this a little more and came up with this idea: I think you only have to count pulses on one of the wires. Since there are 3 wires, you can multiply the pulses on one wire and multiply them by 3.

Edit: Now, how to tap into one of the wires. We are talking about 3-20 (and in some cases even more) volts and sometimes high amps.

just thought i would check in to see if any one made progress towards measuring rpm through the pulses.. i am trying to measure RPM's on a mode car using arduino... but the code posted before does not seem to give consistent rpm output...

i am using novak gtb ESC with 7.4v lipo batter to power a 3.5r brushless motor...

any thoughts?

Thank you!

Can someone please post how to connect the RPM wire properly to an arduino duemilanove. I have seen some fuzzy pictures that show a resistor and a led but no description of how to connect them to the arduino. I want to try and get a fan to act as a POV like the harddrive POV.
thanks
demir57

The 10K is a pull up (or down?) resistor, you connect it from the RPM pin to either the positive or negative wire, I can't remember. The LED is just there to show something is happening, you don't need it. The RPM pin goes to interrupt pin on the arduino.

-Z-

I can not get this to work. I have tried 4 different fans including a CPU fan I know has a working RPM sensor. As it is right now the arduino is just printing random RPM numbers out to the serial console. I can stop the fan with my fingers and nothing changes. Disconnecting the fan all together from the arduino makes no change in the serial output.

Here is how I have tings wired up.


And this is the sketch I am using. (found on page 1 of this thread)

volatile byte NbTopsFan;
int hallsensor = 2;

void rpm()
{
 NbTopsFan++;
}


/***************************************/
void setup()
{
// pinMode(hallsensor, INPUT);
 Serial.begin(9600);
 attachInterrupt(0, rpm, RISING);
};

void loop ()
{
   NbTopsFan = 0;
   
   delay (1000);
   NbTopsFan = NbTopsFan * 30;
   Serial.print ("     ");
   Serial.print (NbTopsFan, DEC);
   Serial.print (" rpm");

   
};