Sensing differential pressure in form of inductance

Using Arduino Sensors
#1

Hello Folks,

Right now I am doing an university project which requires me to use an Arduino for sensing atmospheric pressure. I am using a sensor that represents the difference of pressure between his two inputs in form of two different inductances. While the difference rises or fall, one inductance increases and the other decreases. I did all the testing with a pressure generator and could verify that the inductances vary more or less between 7 mH and 10 mH in both sides with 10000 Pa applied to one input. Both inductances will show more or less 8 mH when there's not pressure difference.

So, in order to sense this with an Arduino, the first thing I did was create a small circuit in form of bridge, having the differential inductances and two equal resistances, and feed the system with an AC signal, so I can measure a voltage drop difference between the two bridge branches (Va and Vb), like the circuit image below:

The best result I could find, after testing different resistance/signal setups (which is the same of the image if I'm not mistaken) was to have a sine wave that varies between 4 Vpp (no pressure difference) and 7.2 Vpp (+10000 Pa difference).

Now I got stuck. I need to convert this sine wave into something the Arduino would be able to read (DC signal between 0 and 5 V). What would be the best option?
My advisor recommended using a comparator to convert the sine to a square wave and then have it through a Phase Locked Loop IC (4046)... I tried reading more about this approach but it honestly made no sense to me. I also tried some other options but had no success so far.

I would be thankful if anyone has any idea regarding such problem.

#2

Blue_Phoenix:
The best result I could find, after testing different resistance/signal setups (which is the same of the image if I'm not mistaken) was to have a sine wave that varies between 4 Vpp (no pressure difference) and 7.2 Vpp (+10000 Pa difference).

This is AC. Positive and negative voltage swing on the coil.
You could try zero crossing detector opamps.
That will give you a switch time difference. Look at the LTspice Va,Vb sine waves at 0volt.
Not sure if an Arduino is fast enough to give you enough resolution.
Leo..

#3

Your advisor wants to measure the frequency (a change in the frequency) and you want to measure the amplitude of the sine. That are two different things.

I would use a third option: use the Arduino as a two LC-meters.
Google for : arduino lc meter

Using a sine with the resistors seems odd. If an inductance needs to be measured, then some kind of oscillator with a frequency and a capacitor is needed. It can be a continuous frequency, or it can be a single pulse.

Some users on this forum know about coils and metal detectors. Perhaps they have a better idea.

#4