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The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

Update: I made a small breadboard with the changes mentioned in the suggested below and jerry-rigged it to the PCB, but was not able to get any reliable readings as the setup was jerry-rigged. I will recreate the entire OP AMP front-end circuit on a larger breadboard.

Will also consider the suggestions made by @Kartman and @EJE which led me to these links: https://www.reddit.com/r/AskElectronics/comments/71jqlq/variable_reluctance_waveform_op_amp_circuit_issues/ http://www.megamanual.com/ms2/pcb.htm

A comparator may be a better solution, but for now will continue with the OP AMP. I am a bit confused about using the (-) or (+) OP AMP inputs correctly. Any benefits to gain in my case to sue one over the other, besides non-inverting (+) and inverting (-)? For now, I think I will be looking at increasing resistor R4 to around 2k-3k which will still give a 5x gain with R1. A larger R4 value I believe will lead to a larger voltage change. I was concerned that a larger resistor will attenuate the signal generated from the coils by "suppressing" the current.

Also, wondering if I should have the two coils in series (instead of parallel, currently) with on end tied to ground and the other to one OP AMP input? Something like this:

It's a comparator with a 1/2VCC input from voltage divider, and other input from two coils in series with zener and regular diodes and load resistor.

The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

Update: I made a small breadboard with the changes suggested below and jerry-rigged it to the PCB, but was not able to get any reliable readings. I will recreate the entire OP AMP front-end circuit on a larger breadboard.

Will also consider the suggestions made by @Kartman and @EJE which led me to these links: https://www.reddit.com/r/AskElectronics/comments/71jqlq/variable_reluctance_waveform_op_amp_circuit_issues/ http://www.megamanual.com/ms2/pcb.htm

A comparator may be a better solution, but for now will continue with the OP AMP. I am a bit confused about using the (-) or (+) OP AMP inputs correctly. Any benefits to gain in my case to sue one over the other, besides non-inverting (+) and inverting (-)? For now, I think I will be looking at increasing resistor R4 to around 2k-3k which will still give a 5x gain with R1. A larger R4 value I believe will lead to a larger voltage change. I was concerned that a larger resistor will attenuate the signal generated from the coils by "suppressing" the current.

Also, wondering if I should have the two coils in series (instead of parallel, currently) with on end tied to ground and the other to one OP AMP input? Something like this:

It's a comparator with a 1/2VCC input from voltage divider, and other input from two coils in series with zener and regular diodes and load resistor.

The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

Update: I made a small breadboard with the changes mentioned in the suggested below and jerry-rigged it to the PCB, but was not able to get any reliable readings as the setup was jerry-rigged. I will recreate the entire OP AMP front-end circuit on a larger breadboard.

Will also consider the suggestions made by @Kartman and @EJE which ked me to these links: https://www.reddit.com/r/AskElectronics/comments/71jqlq/variable_reluctance_waveform_op_amp_circuit_issues/ http://www.megamanual.com/ms2/pcb.htm

A comparator may be a better solution, but for now will continue with the OP AMP. I am a bit confused about using the (-) or (+) OP AMP inputs correctly. Any benefits to gain in my case to sue one over the other, besides non-inverting (+) and inverting (-)? For now, I think I will be looking at increasing resistor R4 to around 2k-3k which will still give a 5x gain with R1. A larger R4 value I believe will lead to a larger voltage change. I was concerned that a larger resistor will attenuate the signal generated from the coils by "suppressing" the current.

Also, wondering if I should have the two coils in series (instead of parallel, currently) with on end tied to ground and the other to one OP AMP input? Something like this:

It's a comparator with a 1/2VCC input from voltage divider, and other input from two coils in series with zener and regular diodes and load resistor.

The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

Update: I made a small breadboard with the changes mentioned in the suggested below and jerry-rigged it to the PCB, but was not able to get any reliable readings as the setup was jerry-rigged. I will recreate the entire OP AMP front-end circuit on a larger breadboard.

Will also consider the suggestions made by @Kartman and @EJE which led me to these links: https://www.reddit.com/r/AskElectronics/comments/71jqlq/variable_reluctance_waveform_op_amp_circuit_issues/ http://www.megamanual.com/ms2/pcb.htm

A comparator may be a better solution, but for now will continue with the OP AMP. I am a bit confused about using the (-) or (+) OP AMP inputs correctly. Any benefits to gain in my case to sue one over the other, besides non-inverting (+) and inverting (-)? For now, I think I will be looking at increasing resistor R4 to around 2k-3k which will still give a 5x gain with R1. A larger R4 value I believe will lead to a larger voltage change. I was concerned that a larger resistor will attenuate the signal generated from the coils by "suppressing" the current.

Also, wondering if I should have the two coils in series (instead of parallel, currently) with on end tied to ground and the other to one OP AMP input? Something like this:

It's a comparator with a 1/2VCC input from voltage divider, and other input from two coils in series with zener and regular diodes and load resistor.

The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

The problem is only in the input stage of the op-amp.

Edited: removed reference to "eddy-current" and changed to "reluctance".

The reluctance-current is generated from two coils by ferrous movement passing through them. The coils are 10 ohm each with 0.254 mH. The current coming out of them is a sine wave that goes positive and negative. The circuit works 95% of the time as it is, but at times it seems that the difference between the two op-amp inputs (2 and 3) is not enough to result in an output.

On the bench, if I simulate things and feed a positive 3 V pulse into J1 going to Pin 2 of the op-amp and also ground J2 (going to pin 3) then it works 100% of the time. Of course, in real life the current is not only positive.

I suspect that when the positive and negative current is generated in the form of a sine wave, at times the input via J2 going into pin 3 of the op-amp overrides J1 going into Pin 2 of the op-amp, thus the op-amp does not put out any amplified signals. Should I change R2 to a lower value like 2-3k, or should I add also a capacitor in series between J2 and pin 3 of the op-amp?

Update: I made a small breadboard with the changes mentioned in the suggested below and jerry-rigged it to the PCB, but was not able to get any reliable readings as the setup was jerry-rigged. I will recreate the entire OP AMP front-end circuit on a larger breadboard.

Will also consider the suggestions made by @Kartman and @EJE which ked me to these links: https://www.reddit.com/r/AskElectronics/comments/71jqlq/variable_reluctance_waveform_op_amp_circuit_issues/ http://www.megamanual.com/ms2/pcb.htm

A comparator may be a better solution, but for now will continue with the OP AMP. I am a bit confused about using the (-) or (+) OP AMP inputs correctly. Any benefits to gain in my case to sue one over the other, besides non-inverting (+) and inverting (-)? For now, I think I will be looking at increasing resistor R4 to around 2k-3k which will still give a 5x gain with R1. A larger R4 value I believe will lead to a larger voltage change. I was concerned that a larger resistor will attenuate the signal generated from the coils by "suppressing" the current.

Also, wondering if I should have the two coils in series (instead of parallel, currently) with on end tied to ground and the other to one OP AMP input? Something like this:

It's a comparator with a 1/2VCC input from voltage divider, and other input from two coils in series with zener and regular diodes and load resistor.