Re: Building a Cheap Tachometer

luki wrote:
Hi,
A small DC motor maybe, i don't know (i don't decide it yet) but would
not be very big sized motor. Is there any circuit that would generally
be able to measure motor speed?

There are many, but you need to specify how. For example, RPM can be
determined optically, mechanically, electrically even acoustically. Allot
depends upon your accuracy requirements, the speed of the motor and how
often you need updates. You could count pulses (magnetic, optical, etc.)
over a defined time interval, or measure the time between pulses. What
works best depends upon your application.

If not, what really caused that? Is there any special attention i must
deal regarding each type/size/speed?

Just the obvious things like hanging a magnet on the shaft of a pager motor
probably won't work well etc... ;-)

At this point, I can only offer the advice that Don
Lancaster would probably give you......use a PIC (and don't try to
get rich by writing books). ;-)

This is the background\purpose of this tachometer :
1. I was developing a motor controller, so i need a speed sensor to
control my motor
2. The motor would be a small DC motor, to be easy to control
Any suggestion about the motor itself?

Is this for something like a robot where measuring the wheel speed/rotations
might be easier/better? Can you be more specific about your end goals?


not really enough info, but you could start here
http://www.national.com/pf/LM/LM2907.html
A cheap frequency to voltage converter would be nice. That means i
must measure the frequency change according to Doppler? What kind of
signal that must be transmitted?
What if I can't have LM2907, quite hard to find things like that in my
country. Is there any alternative. Or could i made frequency to
voltage my own?


I really appreciate your posts. Looking forward to hear more.

You probably shouldn't mix responses from different people into one reply
like this. :-)


.

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