# frequency to voltage converter circuits

#### gani775

Joined Jan 19, 2012
15
actualy i need an frequency to voltage converter ckt. the output frm an rpm magnetic sensor which is in the form of pulses should be converted to voltage. so plse suggest me ideas.

#### wayneh

Joined Sep 9, 2010
17,504
There's also a circuit for using a 555 as a frequency-to-voltage converter. I built it once and it worked fine. I used a guitar tuner as input and got a nice linear response out. The circuit was in the Forrest Mims pamphlet on the 555.

#### gani775

Joined Jan 19, 2012
15
The maximum frequency which i need to feed to an f-v converter is (13-15)HZ.
So please suggest me an frequency to voltage converter which should produce voltage around 5-10v.
Please do send the design of the respective converter.

#### jimkeith

Joined Oct 26, 2011
540
The low frequency is a problem--to reduce ripple in the analog output, a relatively long time constant is required--to obtain accurate readings with low ripple, a time period of 0.5sec to 1sec is required for the voltage to settle--is this time delay acceptable?

Another way to do this is via a microcontroller that measures time between pulses calculates 1/t and outputs an analog signal--relatively simple problem for a high level language code developer--this provides fast response without ripple--probably beyond the scope of your problem--do you agree?

#### gani775

Joined Jan 19, 2012
15
Sir, our project plan:
first we use an magnetic sensor to find the speed(rpm),output of which is pulses, then we are feeding the same to an f-v converter.. to get an output in the range 5-10v.
since the speed is around 800rpm(max),maximum frequency is around 13-15hz.
So please guide me with this.
Please suggest me an f-v converter,with design so that an desired voltage of around 5-12v is obtained

#### gani775

Joined Jan 19, 2012
15
Sir, our project plan:
first we use an magnetic sensor to find the speed(rpm),output of which is pulses, then we are feeding the same to an f-v converter.. to get an output in the range 5-10v.
since the speed is around 800rpm(max),maximum frequency is around 13-15hz.
So please guide me with this.
Please suggest me an f-v converter,with design so that an desired voltage of around 5-12v is obtained

#### gani775

Joined Jan 19, 2012
15
Yes sir that time delay is ok.. and accepted

#### hgmjr

Joined Jan 28, 2005
9,027
You might consider putting magnets at 90 degree intervals if practical. That would give you a 53 Hz signal to work with. It would also keep your rotating disc better balanced.

hgmjr

#### Ron H

Joined Apr 14, 2005
7,063
Is there a minimum frequency that you need to monitor?

#### crutschow

Joined Mar 14, 2008
34,842
I once worked on a feedback motor control circuit which also used a magnetic pick-off to sense motor speed. I had a problem with the ripple. If I increased the RC filter time-constant to reduce the ripple to an acceptable level, it messed up the loop control response. My solution was to add a sample & hold synchronized to the pick-off frequency which thus sampled the ripple voltage at the same point every cycle. This gave a DC voltage with no ripple, that changed in small steps as the speed varied.

#### gani775

Joined Jan 19, 2012
15
Yes sir we need to maintain 13hz minimum frequency.

#### gani775

Joined Jan 19, 2012
15
Sir pls can u attach the design of ur city.

#### bountyhunter

Joined Sep 7, 2009
2,512

#### gani775

Joined Jan 19, 2012
15
Sir when 13hz is fed..wat might be the voltage., when given to lm2907/2917
Can we increase the voltage to about 5v

#### jimkeith

Joined Oct 26, 2011
540
Good device for the application--yes, output may be scaled for 5V @ 13hZ

What is the voltage output level of your mag pickup?

#### gani775

Joined Jan 19, 2012
15
Sir, is there any electronic frequency comparater device.

#### jimkeith

Joined Oct 26, 2011
540
Try this circuit

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#### PaulEE

Joined Dec 23, 2011
474
Alternatively, you could simply program a microcontroller to measure the period of an incoming wave and output a pulse-width modulation signal whose duty-cycle is proportional to the input frequency. An RC filter and opamp will give you your DC signal...or at least, your zero to +5v signal. You can level shift and amplifier/attenuate as you need...

#### DickCappels

Joined Aug 21, 2008
10,246
Or, trigger a one-shot (NE555) from your pulse source, pass the output from the one-shot through a low pass filter. The output voltage of the low pass filter is proportional to frequency for frequencies at which the one-shot duty cycle is low.