How to use timer register for a simple rpm meter?

[garg29]

Hi friends,
i have to make a simple rpm meter for a shaft running between 500 - 2500 rpm. i have to use 89c51 and a optical sensor combination. but i can't understand how to use timer register for it. and secondly during the time the timer counts, will the display vanish or how can i solve the problem. Please help me.
Thanks.

 

[IanP]

how to design rpm meter

First you need a time base of 1s (0.1s...).
How to do this you will find out in posts some days old..

Once you have this time base just count pulses from your optical encoder and multiply 1s result by 60 to display result as rpm.

Btw, Timer counts clock pulses in the background so the microcontroller can do other tasks such as display something et cetera..

 

[garg29]

Re: RPM METER DESIGN

thanks for replying.i will try the same.

 

[neelam]

RPM METER DESIGN

hi ianp, i was trying a search for rpm meter design and i found this page. I think the method you told would give a resoultion of 60 rpm ( 60rpm, 120rpm, 180rpm.....so...on), is there any better method for getting resolution of 1 rpm. one thing more i've to use hall effect sensor with only one magnet, i cannot use disc-optical encoder.
thanks.

 

[IanP]

Re: RPM METER DESIGN

For low RPM you can measure the time of 1 revolution by counting, say, 1ms internally generated pulses and "normalize" the result with 60s by deviding number 60 by the result ..

 

[neelam]

RPM METER DESIGN

ok. i think i understood 50% of that. do you mean to say i should run timer for 1ms and after each 1ms i should increase a register by one. this should be done between to sucessive pulses received from hall effect sensor? then i should do calculations for 60 seconds to obtain RPM????? clear me out, please, as i'm new to all this.
Thanks.

 

[IanP]

Re: RPM METER DESIGN

The calculations should be done like this:

Lets assume that you counted 20 000 of 1ms pulses = 20s for 1 revolution.
To obtain the result in RPM you have to devide 60s by 20s or 60000 by 20000 in ms. The result is 3 RPM ..

Now it should be clear ..

 

[neelam]

RPM METER DESIGN

dear IanP
thankyou so much ..i tried that method and it worked successfully......
thankyou once again for ur kind help
byee
neelam