Subject: Re: frequency to voltage converter
Date: Fri, 17 Jan 2003 09:56:35 +0100
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Meindert Sprang wrote:
> "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 shaft. 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 )
2500 pulses per rotation, 100 rpm: that is 250000 pulses per MINUTE or
4167 pulses per second. And 41667 pulses per second (Hz :-) at 1000rpm.
> 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 tricky.
At the now lower frequency, this will be not such a big problem. If it
is still too fast or your motor goes even faster, you can also
pre-devide the input frequency.