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From: Mark Borgerson
Subject: Re: frequency to voltage converter
References: <email@example.com> <firstname.lastname@example.org>
X-Newsreader: MicroPlanet Gravity v2.50
NNTP-Posting-Date: Fri, 17 Jan 2003 17:52:54 GMT
Date: Fri, 17 Jan 2003 17:52:54 GMT
In article <email@example.com>, mhsprang@NOcustomSPAMware.nl says...
> "anotherbrick" wrote in message
> > i need a circuitry , which will build a speed signal from coming encoder
> pulses .
> > for example i have a 2500 pulse encoder which is connected to a motor
> > when the motor runs at 100 rpm - this makes 250000 pulses / second
> > i need a IC which takes this pulses and builds a signal 0.5 V for example
> > when the motor runs at 1000 rpm it will output 5 V.
> > as you can see it must be very linear.
> > does anybody have an idea ?
> > is there such a IC on the market ?
> > or any other methods ?
> > (i dont want to use a tacho becouse it costs money )
> Normally, you would use a mono-stable multivibrator for this. Triggered by
> you pulse train, the mmv will output a pulse of fixed width with a
> repetition rate equal to the pulse frequency of your encoder. Run the mmv
> output through a low-pass filter and you have a DC voltage indicating the
> speed. And it's linear.
> But creating a reliable mmv with a very short pulse time, 1000 rpm equals
> 2,500,000 pulses, so the puls time must be shorter than 400ns, is very
I see you missed the difference between RPM and pulses/second also. ;-)
24 microseconds is not so bad.
> A different approach was published many years ago in Elektor. They used a
> single CMOS flip-flop, triggered by the signal to be measured. In series
> with the VSS pin and power ground was a resistor and capacitor in parallel.
> They claimed that the current draw of the FF was linear with the operating
> frequency, thus creating a frequency dependent voltage over the resistor.
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