Adapting FreqCount to use two inputs ?

Projects Discussion and Showcase Science and Measurement
1

I'm working on a Uno-based project - a magnetometer for geophysics - that needs to measure two frequencies in the 50-100 kHz range at about the same time to look for a difference,

FreqCount looks like just the job, but it is restricted to a single input pin.

I'm not sure if this is really a hardware restriction, or if FreqCount can be generalised to read two frequencies from two pins.

Any suggestions ?

2

Hi Jarkman:

I suspect you are working on logging data from two FGM-3 sensors.
I gave this a try a couple of years ago.

  1. I used an IC digital multiplexer (a 54153) to alternately connect the two sensors the counter input on the Arduino. I figured it would be good enough to read one sensor then read the other.

  2. I wrote an entire "sketch" to log data from the two sensors to the SD card. BUT I found that the final product was impractical, because the sensors tend to drift.
    Here is a URL that discusses the stability of the sensors IN GREAT DETAIL:
    Fluxgate Magnetometer: Thermal Correction & Long Term Drifts

I can send you more info on what I did. Contact me at ctyoung@mtu.edu.

Chuck

3

Chuck - yes, I have two FGM-3s sitting here. I don't know much about the sensors, I'm building this for a friend who is interested in geophysics, so I've done no research at all myself.

I had thought of the multiplexer wheeze myself, but I wasn't sure how long a sampling interval I'd need to measure an interesting difference. I'd love to hear more about what you did.

Thanks,

Richard

4

Jarkman:
I'm working on a Uno-based project - a magnetometer for geophysics - that needs to measure two frequencies in the 50-100 kHz range at about the same time to look for a difference,

FreqCount looks like just the job, but it is restricted to a single input pin.

I'm not sure if this is really a hardware restriction, or if FreqCount can be generalised to read two frequencies from two pins.

Any suggestions ?

You might want to look at the code on Frequency counter There's a couple of ways to d it there.
Bill