Frequency to voltage converters

[goldfinder]

Do any of you have and recommendations for a frequency to voltage converter. I found several on the net but am not sure which way to do.

I am building a magnetometer with a rather novel design I came up with and I have the mag working but need more accuracy.

Any recommends would be greatly appreciated.

Goldfinder

[ODM]

Frequency or period? What's the frequency span, and how much jitter do you expect to run into? Do you want a differentiating frequency difference detector, or a static one? If you can't spare more details on the design, please elaborate on the signal at least.

[Altra]

I used the LM2917 F to V chip for the mag circuits I was experimenting on. The circuit
was right out of the data sheet. You need to tweek the capacitor and resistors.

The best solution I found was using a pic micro as a frequency counter and skipping the F/V converter.
Most pics have more than one timer. So you can use two sensors as a gradiometer. The sensors are fed into timer0
and timer1 and gated at 1/sec or 0.1/sec. The two frequencies are subtracted to give you the gradiant.

[goldfinder]

Frequency or period? What's the frequency span, and how much jitter do you expect to run into? Do you want a differentiating frequency difference detector, or a static one? If you can't spare more details on the design, please elaborate on the signal at least.

The freq range at present is variable. I used a cheap F 2 V meter and by adjusting the cap I could get anywhere from 200 hz to 10 Khz for earth field. The earths field (1/2 gauss) gave me (the cap set to give a 5 Kz average) about + or - 1.2 Khz when I rotated the sensor 360 deg. What I had in mind was to convert F 2 V and do a differential of the voltage with a opamp and a ref voltage w/ pot to provde the second voltage.

I thought that the cheap meter was truncating the accuracy. I have a much more a accurate freq meter (8 digits) and it provides much more accuracy in rotating the sensor 360 deg. So I figure a F 2 V would enable me to get more accuracy and therefore a better handle in the actual field intensity.

This is to be a field mag and hauling around a large F meter is out of the question.
Goldfinder

[goldfinder]

I used the LM2917 F to V chip for the mag circuits I was experimenting on. The circuit
was right out of the data sheet. You need to tweek the capacitor and resistors.

The best solution I found was using a pic micro as a frequency counter and skipping the F/V converter.
Most pics have more than one timer. So you can use two sensors as a gradiometer. The sensors are fed into timer0
and timer1 and gated at 1/sec or 0.1/sec. The two frequencies are subtracted to give you the gradiant.

I thought of the PIC also. Since I don't need a gradiometer a second freq source would also work as per you description of what you did. Or just calibrate the freq and time the signal.

What kind of mag field accuracy were you getting?

Goldfinder

[Altra]

I thought of the PIC also. Since I don't need a gradiometer a second freq source would also work as per you description of what you did. Or just calibrate the freq and time the signal.

What kind of mag field accuracy were you getting?

Goldfinder

I never reached a point where I calibrated my readings. You need helmholtz coil to calibrate the sensor. Which I want to construct
some day. My goal was to get the maximum change in frequency when I rotated the sensor180 deg N-S. Depending on the polarity
of the winding one direction gives a minimum and the other gives a maximum frequency

What is your mag being used for? The gradiometer set-up eliminates some of the problems when moving through the earth's field. If your mag is stationary then one sensor is okay. You can just log the change in frequency.