Using LED to measure fiber optic vibration

Projects General Guidance
1

Hello friends,
I'am interested in making ultra low cost fiber optic transmitter and measure the reflections when the fiber cable vibrate.

So, I'm thinking to use LED as light source and detector. As you know, when light comes at the LED, it produces voltage.

The schematic will be open:

arduino-led===>fiber optic wire start ===>fiber optic wire end (no reflector).

I'll program the arduino to "fire" the led for a small amount of time and then shut it of and start to measure the voltage on this pin.

What you think? I'm not sure is the arduino is fast enough to measure the reflections.

2

Have you looked at the speed of light lately? The Arduino on its own is not fast enough.

It also depends on the LED you choose. Very few modern LEDs will work like the textbook says.

Are you talking about mechanical vibration modulating the light in the fiber? I'm sure there is an effect but you will need some serious signal analysis to find it. Optic fibers are used precisely because they have almost no outside influence on the light inside.

3

Thank you for your replay Morgan.

Yes, I'm talking about mechanical vibration. When there is a vibration, the usual reflection change.
I'm inking to count the time between the led turn off and the time of the first voltage increase at the pin.

4

You are trying to build a "time domain reflectometer", TDR. Please Google that for fibre optics. Also, the unterminated end of the fibre is a "reflector". What you may be think of is "back scatter" from irregularities in the fiber cladding. Modern fiber optics try really hard to eliminate back scatter because it degrades the signal.

Paul

5

peter3d:
What you think? I'm not sure is the arduino is fast enough to measure the reflections.

Modern fibre optics are extremly low loss, which suggests that reflections are minimal.

What level of variation in signal\reflection are you expecting to see in a fibre that is being vibrated ?

6

You're after something like this - these guys have a whole processor card to measure fiber optic vibrations. Simple 16 MHz processor is likely to be ineffective.
https://fibersensys.com/security-solutions

7

CrossRoads:
You're after something like this - these guys have a whole processor card to measure fiber optic vibrations. Simple 16 MHz processor is likely to be ineffective.
Fiber SenSys | Integrated Security Solutions

Did you thing, raspberry pi will be more obvious to use?

8

peter3d:
Did you thing, raspberry pi will be more obvious to use?

No because a Pi runs under Linux and that makes precise timing on this sort of scale impossible. You also need a proper photo diode designed for the job, using an LED as a photo detector is not going to work.