RPM measurement from a motor tachometer

Hi Edd Niel,

To do motor speed measurement, you need little more intermediate knowledge of Arduino.

There are two ways you can do this.

1. use the Arduino function pulseIn() and count the pulses in 1 second. This will be good starter. Check the Arduino -> References -> pulseIn function.

The second is more accurate, but little complex than the first approach, but uses two interrupts. It is more efficient design

Use Timer1 to generate an interrupt every second (actually 1.04 sec)

Use attachInterrupt(0, countPulses, CHANGE) ; 

// connect the sensor output to either pin2 or pin3 digital.

in countPulses, increment a variable. On Timer1 interrupt elapsed..check count of pulses. This is accurate way of counting pulses..

There is an example of this in my book "freeduino.begin(), the ultimate beginners guide to Freeduino/Arduino platform", you can buy the same on iStore or printed copy on www.bhashatech.com

cheers

sid

Sir? i really have no idea in using these interrupts and i'm quite new to using functions other than

void loop() and void setup(); but i understant the flow of process.

i have to count how many times the digital input pin from the sensor goes to HIGH state every 1 second.

and multiply it by 60 to have an accurate RPM.

next i have to display it in the serial monitor. and to update the speed reading for a time less than 1 second.

but in terms of coding this in the arduino, I really don't have enough idea.. could you please help me in this?

Here's a couple of places with examples for interupts.

http://tronixstuff.wordpress.com/tutorials/

http://www.engblaze.com/we-interrupt-this-program-to-bring-you-a-tutorial-on-arduino-interrupts/

This project might also give you some ideas

http://www.instructables.com/id/Arduino-Bike-Speedometer/?ALLSTEPS

The interrupt approach is very ideal.

Just for the rare cases where a different method may also be needed: another way (slightly more analog!) is to just take the pulses from whatever sensor is generating them, and just put them through an integrator type circuit (could be as simple as a resistor and capacitor). Then, there is a voltage that varies with the speed. You could then read that with an ADC if there is one built-in to the microcontroller.

But the interrupt approach is the most ideal of course. The analog method is useful sometimes if there isn't  a convenient interrupt available (e.g. running the software on a PC).

EDIT: It could also be useful if you are expecting very high speed and if it is not divided down to be convenient for the microcontroller. However  if this is for a car then you know the RPM range.

The interrupt approach is very ideal.

Just for the rare cases where a different method may also be needed: another way (slightly more analog!) is to just take the pulses from whatever sensor is generating them, and just put them through an integrator type circuit (could be as simple as a resistor and capacitor). Then, there is a voltage that varies with the speed. You could then read that with an ADC if there is one built-in to the microcontroller.

But the interrupt approach is the most ideal of course. The analog method is useful sometimes if there isn't  a convenient interrupt available (e.g. running the software on a PC).

EDIT: It could also be useful if you are expecting very high speed and if it is not divided down to be convenient for the microcontroller. However  if this is for a car then you know the RPM range.