laser communication

[bindusar]

hi, i am making a laser communication system as my project work. i am unable to find a transformer having 8 ohm in primary and 1000 ohm in secondary coil having a frequency response of 20 to 20,000 Hz with negotiable loss. the transeformer is shown in attachment. may i get any alternative suggestions for it? i've to submit the project on 1-dec 2006.so pleeeeeeeeeeese help me. i am in KANPUR,UTTER PRADESH, INDIA

 

[Marks256]

Transformer sounds like a simple audio amp transformer to me. You can get these at any RadioShack, or from jameco.

 

[JimB]

Come on now Bindusar, stop slacking and get the bus to the RadioShack store in downtown Kenpur! If RadioShack dont have them, try Jameco, they are just around the corner.

OK, maybe not!

I dont think that the transformer is all that critical. Just about any small audio transformer will do. Maybe even a small mains transformer, 240v to 12 or 15v.
Use the 12v winding as the 3ohm and the 240v winding as the 1000 ohm.

JimB

 

[bindusar]

question still arises

i am using laser torch at the sending end as a transmitter. but tell me what's the use of an audio transformer before laser, we know that the transformer of 8 ohm in primary and 1000 ohm in secondary will amplify the voltage but reduces the amount of current so as to maintain the total power at output equal as that of input. i am getting the same amount of fluctuations in the beam of LED with and without using that transformer.
further i am using LDR instead of solar cell, but not able to listen the trasmitted sound at the receiver end. only got few distortions when i amplified received signal by a power amplifier.
my doubt is on the sensitivity of that LDR.
please help me.
what power of speakers should be?
may i get the rating of LDR as i am living in a rural area.

Pleeeeeese

 

[i_build_stuff]

The solar cell won't be able to respond fast enough. You want to use a photodiode / phototransistor for that.

Also, I don't really like that circuit you're using. The AC power in the laser beam (the useful part of your signal) still has to come through the transformer, the LEDs across the secondary will introduce horrible distortion, and the DC current in the transformer secondary will probably saturate the core. All you really have to do is feed the laser diode from the collector of a transistor, and either run the transistor in class-A (straight audio), or PCM (digital audio).

 

[audioguru]

Bindusar,
You posted this topic twice. Didn't you see my reply in your other post?
Next time, please don't post topics twice.

Your LDR circuit needs a DC load like this:

 

[Hero999]

I wish people would kindly refrain from posting the same thing more than once, it doesn't help people help you, it only pisses them off.

 

[bindusar]

thank you all for helping me.
now my project is working fine and i've submitted it.
i've made the transmitter and receiver.
i am attaching there pics as well as circuit diagrams i've made.
i'll be back soon with my next project...
thanks again

 

[Marks256]

Wow. Most people asking for help from your side of the world never actually show us what we helped them with!

Nice job

 

[Sceadwian]

Nice housings, looks like a solid project. What kind of performance do you get out of it?