burning out units (audio over laser)

[ecks]

Hello,

Im currently doing that audio-over-laser experiment, using cheap-from-china <5mw units, similar to these -

In testing, i used a transformer that i found in the lab - a bench one, with no measurable resistance across the coil.

(to quickly summerise, the experiment uses a transformer, with equal turns on each side, to modulate the lasers power feed - power to the laser goes through one side, and the audio signal goes through the other)


Anyhow, the experiment works nicely. The audio modulates the laser intensity nicely, and, shining it on a small pv cell, allows a signal that can then be amplified back up again.



I can leave this running for hours, no problem, however, i have burnt out a few lasers by messing with the apparatus, and im not entirely sure how im managing it (hence this post!)


My secondary problem is that i want to build all this kit into a battery powered box, so as i can just put it on the desk, and it works (without mains power, wires, large transformers, etc)


I tested with one of these -

Vigortronix VTX-101-1604 PCB Audio Transformer | Rapid Online

and the setup still works, but i need to increase the psu voltage in order to get the same 'power' (brighness) from the laser, due, i assume, to increased resistance across the transformer coil.

And then, somwhere in the experiment, i burnt out the laser again (theyre pennies from china, but even still, noone likes wrecking things)


Anyhow, i suspect someone here has done this before, or could advise better on how im managing to fry them (too much ampage, but its still confusing me some). Im not so good at the maths side of this, so failing on implementation.

Im considering a 9v battery, then a 5v regulator, then a fixed value resistor (chosen to supply the correct voltage post transformer resistance) then the diode. But im not sure that's the best way?

Thank you, and apologies for the longer than normal post!

 

[Laser Chick]

Hi ecks :wave:

Welcome to the forum. Where are you from? Members might suggest you get certain items and those items might not be able to ship to your country.
Your post is fine and giving detailed information like you did helps with getting good help.
Hang on and help will arrive very soon

 

[Cyparagon]

What is the peak voltage supplied by your audio amp output at the moment?

Have you considered using a more powerful laser module, or perhaps paralleling some of the ones you have?

Do you have a schematic of your setup? The diode will half-wave rectify the audio, so I don't see how you're getting a useable signal out of a PV cell.

 

[ecks]

Hello,

Im located in the united kingdom (england)

Im not sure what the peak voltage is from the amp - ive used three sources so far - a couple of portable tape/cd/radio things (old, as you can guess by the tape!) and a mobile phone.

Im only using the headphone jack on each - i would imagine that all devices put out fairly standardsised voltages on the headphone jacks, else there would be compatibility issues?

Anyhow, as for schematic - i can describe it easy enough - its very simple -


Tip and GND from headphone out run through one side of a transformer.

+ve to laser run through the other side of the same transformer, and then onto the laser. -ve from laser run direct to -ve of the power source.

This allows the audio source to modulate the lasers power, so as it runs between full power, and 'dimmer' than full power.

The psu is adjusted to give the +ve voltage at the laser.

Using the transformer to modulate the power is the key - you can see that the laser is always powered, but just that the intensity changes. This is why its not half wave rectified - the whole wave is preserved - at no point does the laser shut off entirely.


The laser hits the pv panel, and creates a fluctuating voltage, that, whilst its offset (all in the +ve range) it is not half wave rectified. The entire waveform remains, but its just offset into the +ve range.

This is then amplified up. Ive not tried to remove the offset with post processing, however, the amplifiers may be doing that without my knowledge.


I do not want to use more powerful units because

a) i dont need to (the setup works fine at the moment - untill i try and change things and burn out units)

and

b) this is to teach kids. at <5mw precautions need to be taken, but (from what i read) the chance of injury is minimal


The issues im having (buring out units) are not relative to the power of the unit, but the issue that im (evidently) giving them more power than they can handle.

I guess more powerfull units would allow me more margin for error (as in i could run them at lower power, and then have a headroom) but, again, this is for demonstrating aspects of physics to kids, so i really dont want to do that.



Im wondering if i need to scope the power line feeding the laser... The audio signal may (i guess) be modulating the supply voltage more than i think and pusing it overvoltage that way.

Ive been using 3v units. Possibly 5v units (with the same output power) would give me more range / resolution (ie more space to make mistakes in)?


Basically, i have the device working, but am evidently making mistakes when i mess with it (as in it will work for hours unattended, and i might start altering things, and kill it in moments)

The obvious answer is "dont mess with it" however, i need to do so, in order to repackage it, and use slightly different components. Maybe i was just lucky when i first built it, but now i need to understand why i sometimes manage to kill the diodes.

Ive just ordered another 20-off from china, so that should keep me going for a while (ive managed to kill 4-off in my testing so far - but, again, irritatingly, all 4 of them were post getting the device working!)

Thank you!

 

[Cyparagon]

the setup works fine at the moment - untill i try and change things and burn out units

So the obvious follow-up question is: What are you changing?