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Digital tachometer schematic?

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randika

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tachometer schematic

Hi all.
I'm new to this list and I'm an 2nd year EE engineering undergraduate.

I'm building a tachometer for a project in the university.

I need some schematics which generate a pulse after receiving an IR beam.

I'm planning to generate the pulse as follows...

1 > stick an IR reflecting piece of tape on the rotating shaft
2 > sending a continous IR beam using an IR led
3 > receiving the reflected IR beam generating a pulse

then

4 > measuring the time between pulses
5 > calculating the RPM

Is my plan correct..

If u've got some schematics for this the please send me.

Thanks,

cya

Randika K
 

Sputnik

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digital tachometer schematic

Yes, I would say you were on a good path, except it may be simpler if you used a microcontroller. I'm going to use the PIC as an example as that is all I know. The current from the IR receiver is fed into the PIC's RA4/T0CKI. The PIC waits an exact and programmed time, while the TIMER0 increases with every pass of the reflective tape. When times up, the value is in TIMER0 is calculated and displayed on whatever display you choose.

Regards,
Sputnik :idea:
 

chupos

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tachometer schematics

hi
I'm also thinking about making a tachometer, but with a different approach. I would stick a ferromagnetic, kinda circle, to the rotating shaft, with one 'cut' into it. on one side of the circle put a small magnet, and on the other side a Hall sensor. The hall sensor would give u a nice pulse you can measure with a PIC microcontroller for example.
 

raghav

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led tachometer schematic

CHUPOS idea is brighter as compared to others. Try that!
 

Sputnik

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pic tachometer schematic

I disagree, the use of a magnet means the wheel being monitored will be off-balance. If you can balance it, which will be very diffcult, it wll still have some vibration and the posibility of the magnet being flung off due to centrifugal forces, which can become extreme when higher RPMs are reached.

Sputnik :idea:
 

chupos

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digital tacho hallsensor schema

You don't attach the magnet to the rotating part. The magnet is fixed, but a ferromagnetic ... circle is attached to the rotating part. it is perfectly balanced, just two cut-ins at each side of it. the hall sensor gives a pulse whenever the cut-out part of the circle is between the magnet and the sensor. It doesn't give the pulse when the ferromagnetic part is between them.
 

dualcorecpu

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pic used digital tachometer circuits

You can consider to use Frequency-to-Voltage converter (check TI or NS website). In this case, you need a ADC to read the voltage and translate it to the appropriate speed (rpm) value.
 

chupos

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schematic digital tachometer

you can actually just connect the hall sensor or whatever sensor to a MCU (for example a PIC) and time it.
 

randika

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digital tachometer circuits

Hi all,

Thanks a lot for helping me...

I built the sensor part and it is working well... Here are the things what I did.

I used an IR LED and sticked a piece of reflective tape on the motor shaft (please note that motor shaft is black).
Then I used an IR sensor from an old mouse and put some electronics(741 OPAMP and 311 comparater).

When the motor shaft is rotating now I'm getting a nice stream of pulses. It is working well for a distance of 4 inch from the motor shaft without a problem.

Since I'm new to microcontroller programming I need some help from you.

I must use the pic16f84 uC and the RPM should be displayed upto 4 digits(LED ssds). (i.e. 0 - 9999). Can I do this using this uC?

Another problem on the idea of Mr. Sputnik ....
I could not understand what you are saying about RA4/T0CKI and the TMR0...could you please explain it more...

Is it better to generate an inturrpt by giving the pulses from the IR receiver to the RBO/INT pin? which is the better one?

cya

Randika K
 

chupos

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741 tachometer

hi :)
basically you can use any PIC with timer, look at this Application Note by Microchip:
**broken link removed**
If the link doesnt work, its the Application Note AN592.

This is the basic way to get the frequency. To display it is pretty easy using any character LCD, and googleing a lil bit about the controller.
 

jonw0224

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tachometer pic schematics

randika,

You can measure time either way (with RB0 and interrupts) or using TOCKI.

If you use RB0, I would tie TIMER0 to the clock and at each RB0 interrupt calculate elapsed time using TIMER0. You will also have to handle TIMER0 overflows (I would use interrupts for this as well). The main program can calculate and display the time on the LCD when a time has been calculated by the interrupts.

If you use T0CKI, you would write a loop that executes in a specific amount of time and use TIMER as the count during that time (again you have to take into account TIMER overflow). Using this method you want to set the loop timing so that you avoid TIMER overflows (if you use interrupts to handle them, you will affect the time it takes the loop to execute).

Hope that helps.
 

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