Voice via Lan .. My design ..

Voice via Laser .. My design ..

I want to send voice via Laser.
I also search on the net but i did not find any thing meaningful. I don't want to use transformer, all the circuits on the net have transformer used in it.

I am student i don't want to buy, i want to build.

This is my design in the pictures.
I want to ask experts that this circuit will work, if not then tell me what is wrong in it.

It's rather crude, but may work? - assuming the laser will accept AM modulation in such a fashion - and low audio quality is all you need?.

I would also suggest AC coupling the receiver opamp, no need for the LDR to be DC coupled

Of course the communication is AM along with all the reception problems with AM like interference. Using a high frequency carrier with FM modulation would be much better.
Of course the laser must shine on the photocell or it won't work.
Of course the circuit doesn't have automatic gain control like an AM radio so the sound will be very loud when it is close and very weak when it is far.

I modified your transmitter circuit to include the non-linearities of the transistor and the laser in the negative feedback loop of the opamp for distortion reduction.

AM modulation Laser vs LED

AM modulation Laser vs LED
1. Laser
X20 to x100 times the cost of a LED
narrow beam width means makes receiver alignment crucial

design:
A laser has a threshold current (say 7ma) which varies with
temperature

laser bias below threshold say 5ma means
optical output = 0
the output will remain ZERO until the positive peak of signal exceeds the assumed threshold (7ma)


Laser bias current must be (say) 15 ma
10ma bias current
5 ma operating current.

An electrical mishap can immediately destroy the expensive Laser
..................................................................
2. LED
40 degree beam angle, the resulting light intensity at the
receiver will be much smaller than a laser operating at the same current.

The LED intensity will be difficult to vary while controlling
its distortion. The LED must be enclosed in a feedback to the amplifier driving it.

For experimentaion a cheap LED is all that is required.
with minimum receiver range.

A LED photo-diode receiver will have to be x100 times the
sensitivity of the Laser photo-diode receiver:
since the LED light intercepted will be X100 smaller.

Receiver component Noise will be far more obvious
in the LED photo-diode receiver.

The Laser approach is NOT for beginners.

hawk2eye

hawk2eye said:

1. Laser
X20 to x100 times the cost of a LED
...
the expensive Laser

Click to expand...

Where do you shop??

I can buy a laser pointer for $1.00 at The dollar store. It shines on car licence plates and reflects from them all the way down my fairly long street. It comes with 3 button battery cells that last a long time.
The Dollar Store also has a keychain LED flashlight also for $1.00.

Please give me an idea to make a high qality audio laser transmitter.
it should be simple and transformer less.

In my Forrest Mimms Engineer's Mini-notebook: Communication Projects, a PFM (Pulse frequency modulated) transmitter and reciever are detailed. It works simply with a 555 chip supplying pulses to a LED/Laserdiode and the frequency of these pulses is varied via the devices frequency control pin 5. The carrier is filtered out on the reciever.