Frequency to voltage conversion...

[Externet]

Hi.
Does anyone knows a simple schematic diagram for frequency-to-voltage conversion using simple components ?
Miguel

[ecerfoglio]

I don´t have a scematic at hand, but you can try this:

A simple frequency-to-voltage converter is a one shot timer (555 family?) to ensure a constant pulse width, followed by an integrator (resistor in series and capacitor to ground).

Choose the pulse width so the max. frecuency you will convert has a longer period (1/frecuency).

Choose R and C so it´s time constant (RC) is larger than the period of the min. frecuency you will convert.

The output will depend on the ratio of the timer´s periods: Ton / TTotal.

But Ton is fixed and TTotal is 1/frecuency.

You may add a buffer so you don´t load the integrator.

[Robert Reed]

Exter
Google up LM2917 and check it out. Its a frequency to voltage converter. If you decide on this chip, beware of one thing--it requires an input with a duty cycle of 25% to %75%. They dont tell you this on the data sheet!

[Chris Smith]

9400

[RS 276-1790] if Rat Shack still carries them?

I have the schematics if you need them.

<small>[ October 28, 2005, 06:51 PM: Message edited by: Chris Smith ]</small>

[josmith]

It depends on what you call "simple". A basic stamp can read very low frequency in period mode or higher using it's pulse in function. Output the result as a voltage with the pwm function.

YOu can make a charge pump with two diodes two capacitors and a resistor.

[Externet]

Thanks, fellows.

The project is to have my cable driven old speedometer running from a modern transmission that outputs reluctor pulses.

The plan was/is reluctor F->V with a LM2917 and back to V->F with a NE566 to supply calibrable clock for a MC3479 stepper driver for the motor attached to the speedometer... convoluted, yes.

The NE566 and the MC3479 stepper driver and the stepper motor work. My LM2917 refuses to work; perhaps I alredy blew it.

The 9400 sounds as a good candidate, did not know it existed, thanks. Got the datasheet now.

Cannot get over ~500 rpm from the stepper motor. Perhaps it's not capable of much more.

Well, back to the bench.
Thanks !,
Miguel

[Dean Huster]

The nice thing about the LM2917 is that one was on the spindle motor controller board on the back of every 5.25" disk drive in existance -- or so it sometimes seemed. After harvesting the components from hundreds of those drives, you build up quite a stock! So, for a free F/V chip, find an old PC.

Dean

[pebe]

You could use an XOR or XNOR gate. Feed the waveform direct to one input and via an RC network to the other. You get a fixed width pulse out every time the waveform changes polarity. Then integrate the pulses and measure their mean level.

[craig-1]

YOU CAN FIND THE 9400 AND WORKING CIRCUITS IN THE BOOK BY FORREST MIMS PAGE 128 & 129 THE FORREST MIMS ENGINEER'S NOTEBOOK