Simple. I will investigate and compare the frequency response of various photo detectors.

Just to know, the majority of the projects that I've tried replicating are using a solar cell. Very few use photo diodes/resistors etc.

 

Well, the distortion could be from any one or several parts of the system.

I don't have enough information about the components involved, so I have to start by speculating.

The laser diode needs a driver. The driver needs to provide constant current to the diode, and there are a couple of ways it could do this. Depending on the rated input of the diode, it may be a buck or boost converter. It could also be based on opamps but so far as I can tell that's very unlikely.

Those converters convert the input to AC internally to make the change. I don't really know, yet, how that could be interacting but it is a place I would look.

 

Hello,

I have loaded the sample2.wav into audacity and normalized it to get a higher amplitude to -1 dB.
I have taken a view waves from the middle of the centre and they show more distortion than the ones @Yaakov showed:


I do not know the difference, as I do not know where @Yaakov did his sample.

Bertus

 

Well, the distortion could be from any one or several parts of the system.

I don't have enough information about the components involved, so I have to start by speculating.

The laser diode needs a driver. The driver needs to provide constant current to the diode, and there are a couple of ways it could do this. Depending on the rated input of the diode, it may be a buck or boost converter. It could also be based on opamps but so far as I can tell that's very unlikely.

Those converters convert the input to AC internally to make the change. I don't really know, yet, how that could be interacting but it is a place I would look.

Let's assume that the scenario you describing is simpler than it looks and I fully understand what you are saying, how can i physically do tests on such small components. The laser diode is enclosed in a metal casing.

Also, I'll be posting a reply with more info about the parts so anyone can have a better overall look

 

One place I would check is at the input to the diode. If would help to see of the source is distorting, or only the receiver is.

 

Hello,

I have loaded the sample2.wav into audacity and normalized it to get a higher amplitude to -1 dB.
I have taken a view waves from the middle of the centre and they show more distortion than the ones @Yaakov showed:

View attachment 174964
I do not know the difference, as I do not know where @Yaakov did his sample.

Bertus

@bertus I used the last sample. Your method removes my playback device and is better.

 

Hello,


I do not know the difference, as I do not know where @Yaakov did his sample.

Bertus

Using Audacity, this is an equivalent section of the last sample in the file. So maybe it is somehow frequency dependent.

 

Parts used in the project:

Laser module: https://grobotronics.com/laser-module-650nm-5mw-point-type.html

Solar Panel: https://grobotronics.com/solar-panel-2w-136x110mm.html

Amp: https://www.adafruit.com/product/2130

The 2 tranformers I tried were bought bulk from a local hardware store, thus I lack any datasheets or links. Though, I did some measurements on them and i present them below with exterior photos of them.

Transformer No1:


Transformer No2:


Measurements:

 

One place I would check is at the input to the diode. If would help to see of the source is distorting, or only the receiver is.

How could I check at the input of the diode?

 

Without modulation, you will get interference from just about anything.I'd suggest n I-V converter on the solar panel and modulation.

 

Hello,

Here I made a screenshot from the last part of the sample2.wav:



It looks like in this sample there is a cross-over distortion.

Bertus

 

Hello,

Here I made a screenshot from the last part of the sample2.wav:

View attachment 174972

It looks like in this sample there is a cross-over distortion.

Bertus

How could I eliminate this distortion?

 

Hello,

Could you make a schematic of all parts used?
That way we can have a look how to improve it.

Bertus

 

Hello,

Could you make a schematic of all parts used?
That way we can have a look how to improve it.

Bertus

https://easyeda.com/AnthonyKpS/Laser-Transmission-with-an-Audio-Amp.