Free Space Communication (labview).

Hello! I'm new to the forums, currently in College with several electronics classes. I'm currently working on a project in my free time which I'd give to gain some insight from those smarter than I. The purpose of the project is to construct a free space communication device via modulated laser diode. The first 'milestone' goal is to use modulate a song over the beam to a photo-detector to speaker. The following is my current progress.

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Step #1 : Power the laser - The first purpose of this circuit was to provide constant current to a laser diode. I achieved this using the 50kpot as the input to U1A-pin3. By adjusting the pot I was able to limit the current flowing through the led regardless of voltage changes at the VR1-collector.

Circuit [source] | LM324n (U1A) [datasheet] | Tip122 [datasheet]​

Step #2 : PWM Test - Moving forward I replaced U1A's input with a [myDaq] PWM output signal. The output signal was generated from a 8bit .wav file. I replaced the led with a small speaker and was successfully able to play an 8bit mono wav file through the circuit and listen to it via the speaker. I've attached the LabView file.

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Step #3 : PWM Modulate The Laser - I'm currently having issues providing enough voltage to power the laser. The signal coming from the DAQ is 1v, is it possible to somehow bias the laser to run at low intensity and then input the same signal resulting in a laser powered 100% of the time that vary's intensity across a photo-detector?


Any help / thoughts / suggestions / comments etc would be greatly appreciated and welcome! I'm also willing to hear suggestions on more efficient ways to accomplish this task.




Step #4 : Capture laser data - coming soon
Step #5 : Play Song - coming soon

 

Hello ScottWang,

1. It isn't homework it's a personal hobby / project though it is related to my field of study.
2. Will do!
3. No I didn't and I've provided the link to the source in the write up!

Thanks

 

I'm not using the circuit from the link you provided, I'm using the circuit from the link I referenced. At this time point he's discussing the advantages of this circuit over using LM317 which I commonly see used for laser-drivers & here he discusses using the circuit with PWM.