Frequency to voltage converter for rudder indicator system

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engineernate2782

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Greetings,
I am looking for a way of converting an output frequency to a DC voltage for a rudder indicator system onboard the boat I work on.
The the output frequnecy of the rudder position sensor varies from 2500 Hz (full left rudder) to 4300 Hz (full right rudder) with zero rudder being 3400 Hz. I have an existing rudder angle display but it operates on changing DC voltage (0-24Vdc). I would like help making the two peices work together, maybe via a LM2917 or other similar frequency to voltage converter? Thanks for any help.
 

Sure you can. You need to build a PLL loop. You will just work it backwards because the DC voltage is used to control the frequency by applying it to a varactor diode in a VCO oscillator. The DC voltage is produced from a phase detector/comparator which compares the frequency to usually a crystal controlled reference oscillator. This might be the zero rubber value in your application. I am not familiar with the LM2917 but I assume it is used as a transducer of some sort. This is very doable and PLL is precisely what you need.
 

hi,
Look at this link:
**broken link removed**
 

I would also check the LM331 data sheet and applications notes on the National Semiconductor website.
 
Alright I just pulled down the data sheet on the LM2917. All it is, is a single stage of what could be used in a PLL. It's OK if your not looking for a high degree of accuracy. I mean, where is your reference? If I was to do this, I would not even use that chip. I would use something like a Motorola PLL IC which has both a phase detector and phase/frequency detector. You would compare this against a crystal reference oscillator so that the tolerance would be that of the crystal. Just my opinion.
 
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A crystal reference oscillator!! To indicate the position of a boat rudder!! Have you gone mad?

Mike.
 
Yes, use a 2917. I sometimes just do it like this...

This assumes your peak-to-peak input voltage is regulated, otherwise you will need to use that second opamp in the 8-pin package as a comparator. This is essentially what's in an LM2917.
 

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A PLL used as a frequency-to-voltage converter is only as linear (or usually, nonlinear) as the Fout/Vin transfer function of its VCO. You are apparently highly enamored of PLLs right now, but your idea is half-baked. An LM2907/2917, plus an op amp, is probably the simplest and most accurate solution to this problem.
 
You could steal a simple idea that Sony used in its '70s era B&W videotape machines to convert the off-tape FM to a DC video signal:

Just have the FM signal continuosly trigger a monostable multivibrator. The more often it is triggered (the higher the FM frequency), the more the output DC rises.
 
I have done a little more research and found that the output of this system needs to be 75 Hz per volt for my purposes. I looked at the LM 2917 PDF from the National website and have seen some similar systems to what I am trying to do. I just need some help on how to determine the correct capacitor and resistor values. Once again thanks for the help, input, and ideas
 
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