I am conducting a scientific experiment to **approximately** measure the entering velocity and the leaving velocity of a magnet through an electromagnetic coil.

Beside the coil are two lasers and two LDRs as depicted by the figure below.[![enter image description here](https://i.stack.imgur.com/R56aq.jpg)](https://i.stack.imgur.com/R56aq.jpg)

I expected this circuit to generate a rising edge and a falling edge, but I realized only after testing on the oscilloscope that I was not able to receive a square waveform to input to my MSP430 MCU as interrupts. My plan was to calculate the time between these two interrupts.

However, the waveforms I observed were as below. [![enter image description here](https://i.stack.imgur.com/uX0MI.jpg)](https://i.stack.imgur.com/uX0MI.jpg)

Then I thought that I could use an LM358 in front of my voltage divider. This is described in [here](http://www.instructables.com/id/LASER-Tripped-Wire-Alarm-Circuit/). But looking at my practical waveforms I observed from the oscilloscope, I am doubtful how I can tune the comparator. Is there a better way to achieve my task using better electronics? I am not limited by component costs, however, I am not willing to buy a ready-made apparatus for this purpose. My intention is to develop one. 

Thank you for your views and help.