Laser Link Communicator

[kabilan]

Hi guys,

I'm in an attempt to make a school project which will enable audio transmission over a laser medium 5mW/650nm. Here is the link where I got the idea http://captain.haddock.8m.com/laser/laser1.html . Does anyone ever tried building this circuit, was it working?

I surveyed electronics shops for available materials for the construction. I found that I have to replace 2n5484 with 2n3819, and bc549 with pn2222 since it was not available. Is this just okay?

I have a question with regard to the section where there is a 68 ohms NTC thermistor, the problem is there is no available 68 ohms but there is a 10 ohms NTC thermistor.  What should I do with it? Is it okay if I removed the 68 ohms from the circuit or replaced it instead with the 10 ohms?

Any ideas is greatly appreciated.

regards,

Kabilan

[audioguru]

You can't use 10 ohms to replace a 68 ohm resistor, you risk burning-out the laser diode.
Since you can't use the proper NTC, the laser might drop-out when the ambient is cool and burn-out if hot.

The photo-diode is backwards in the receiver's schematic, the pcb layout of it is correct.

[kabilan]

hi guru,

Thank you for the idea, I appreciate it.  :D

Since you can't use the proper NTC, the laser might drop-out when the ambient is cool and burn-out if hot.

Is there any alternative I can do about it? What can I replace with that section?

The photo-diode is backwards in the receiver's schematic, the pcb layout of it is correct.

I see.... does that mean the photodiodes do have polarities? How should I be able to identify which terminal should I connect with it?  (I should do some more research with photodiodes  ;D)

[audioguru]

Is there any alternative I can do about it? What can I replace with that section?

Try it with your 10 ohms NTC in series with a 56 ohm resistor, and don't let the ambient temp change very much.

does that mean the photodiodes do have polarities? How should I be able to identify which terminal should I connect with it?

Of course, all diodes have polarities. Look at its pic in its datasheet.

[kabilan]

hi guru,

Thats great news, now I have some hopes  ;). I will start constructing it and try your suggestion. I will let you know how it would go.

Thank you very much, you ROCK!!! You are very cool  8)