What am I doing???

[norbyx]

So I don't really know what am I doing but I know maybe someone can tell me.
Here is the deal,
I was reading over at Sam's laser FAQ how to make a super cheap laser meter, and after reading part of it a thought crossed my mind, my sons broken mini helicopter, it was controlled by IR and it had to have a receiver... So I go and take it apart and find this

The receiving unit, I hook a multimeter from the center pin and ground and point my 532 laser at it, the result I get a 0.5 volt reading....
What am I doing??? What is this 0.5v reading? Is it just IR comming out of the laser?
If I get the receiving sensor close to a light bulb (ac filament regular bulb) I also get a reading out of it...
Could someone enlighten me?

 

[Bionic-Badger]

Those receivers are for IR data transmission (IR remotes, etc.). They're like these types of modules, and produce a digital signal from a signal at a wavelength of around 940nm, usually utilizing a 38khz carrier frequency. Many are also designed to suppress constant noise sources like lights or other repetitious signals.

That device won't work for a power meter sensor. If you want to use a sensor like that for a cheap power meter, you'll need to get an IR photodiode or photoresistor. They'll probably be more sensitive to the wavelengths you'd want to use anyway.

 

[Cyparagon]

^That isn't a photodiode? I don't think a phototransistor would produce voltage, would it?

It's neat how that black casing is actually transparent to IR. Photodiode(transistor?) out of an old stereo:

Viewed with IR camera:

 

[norbyx]

Ok,
So looking at the module data sheet there is a thing I don't understand. The pin 3 Vs and Pin2 GND are the ones I am getting a voltage out of.
Obviously the mini heli is powered off, and the voltage is present only with the light pointed to it.
If this device is sensible to IR wavelength it means that the reading I am getting is just the IR part of the green 532 laser? Since I haven't received my LPM yet (hope I will soon), I have no way to test the purity of the laser. ...

 

[Sigurthr]

Just as an aside, a LPM won't inherently tell you if your DPSS laser is IR filtered or not, and with such concentrated light it is possible green is getting through the casing filter. You can place non-IR-blocking goggles between the laser and LPM and measure the output and you will get most of the IR through in most cases, but not all of it as there is always some attenuation (if from nothing more than reflectance). Doing this can ruin your goggles if your laser is powerful enough though.

Often, photodiodes/phototransistors/LDRs will become totally saturated when exposed to lasers as they were not designed for such intense light sources. So the only info you'll get out of it is that there is light shining on it, which doesn't help you - you know that already. You can take a simple magnifying glass and a simple solar cell and arrange the laser, lens, and solar cell so that the lens spreads the beam out to cover as much of the solar cell as possible without any light spilling over the edges. Place the whole thing in complete darkness and measure the voltage and current out of the solar cell. You can use this to get comparative measurements of your lasers but you won't get any actual readings, and the results will only work for lasers of the same wavelength as the solar cell won't have a flat response to different wavelengths.

 

[Cyparagon]

Yes, the IR from the green is causing the voltage you see. It doesn't take much at all to cause a voltage. Consider it can read a teeny LED from the other side of the room. Pointing even 1mW of IR into it is potentially hundreds of times more intense than the remote-control input it's used to seeing.

 

[norbyx]

Ok,
I get the picture now. Well I was just testing... I wasn't going to look to make a LPM out of a broken remote control heli, I just wanted to see what the reaction was to a laser, in any case I compleately understand that I am not going to see the ammount of IR out of my LPM, I know that placing the goggles before the sensor is a way of testing it or also placing an IR filter and seeing how much the power drops....

It is understandable that a receiver that is made to read the signal of a small led will be topped by a laser that is much more powerfull...

Well thankyou all for your replys.

 

[Bionic-Badger]

Well those three-prong devices like in that helicopter and TVs are powered and then produce a signal out of the third pin. Besides some additional power filtering, they're essentially plug-and-play as far as digital IR signals are concerned.

 

[scumbagatheist]

Well done on the DIY research! It's just a shame it didn't work out the way you wanted...at least you learned something new about LPMs, IR, etc.

Thanks for this thread. I learned something too!

 

[norbyx]

Well just a quick update on this thread. Yesterday my 200mw green laser came in.... so I just did some testing today. Fact is that you can clearly see a response difference from my previous laser (that I still have to LPM as soon as the laserbee gets here next week).
But for a comparative way of measurement it might be a cheap solution, now today I am going to pick up 2 blue lasers one should be a 65mw and the other a 1.2W. So will post more results this afternoon. I want to see if the module tops off after a certain point or not. But for now my conclusion says that if one was to compare two lasers of the same wavelenght just to know wich one is more powerfull without any specific reading, this might just work.

 

[scumbagatheist]

I'm very jealous about your LPM coming! Mine will have to wait until I sell the SAiK.

 

[norbyx]

Ok new update, my new blue lasers just got in... so I tested them with the heli module and the result was ZERO, nada, zip, nothing....:yabbmad:
I was suspecting this wouldn't work for lasers that don't produce a IR signal, but deep inside I was hoping it would.
Anyway, it is a good cheap way to determine if your green laser is IR filtered or not....

 

[123splat]

Try replacing your IR rcvr module with a plain old LED. The clear ones work better, but any will do.

 

[Cyparagon]

for a comparative way of measurement it might be a cheap solution

Or just take readings from one of your trichromatic ocular devices. Most of us already have at least two

 

[scumbagatheist]

Or just take readings from one of your trichromatic ocular devices. Most of us already have at least two

THIS!

:crackup: