reading an analog signal

Hello,

I'm french, sorry for my poor english ! :)

I have a school project, i would like to send an information using a laser with rx and tx.

But i don't know what to use to receive the analog signal. I have a phototransistor but i only manage to send frequencies.

I would also like to know if it's possible to catch the "tone()"

Thanks in advance ! Yoann

What kind of analog signal?

Normally you don't send analog over optical.

Lasers, LEDs, and phototransistors are non-linear, and there are signal losses.

So the normal thing is to convert the analog to digital, transmit it, and convert back to analog.

There are two basic ways. One is CW ( or also a single tone ). The other is FM. Sending a tone has the advantage that is isn't just ambient light. If you can receive the tone as on/off type signal, you can time the rate of the signal with something like micros(). With FM, you use two different frequencies to be 1 and 0. Have fun. Dwight

@Dwight - how do you get FM on a laser? Lasers are basically turned on and off so your modulation choice is limited. Normally pulse width modulation can be used to send analogue signals.

Grumpy_Mike:
@Dwight - how do you get FM on a laser? Lasers are basically turned on and off so your modulation choice is limited. Normally pulse width modulation can be used to send analogue signals.

You modulate the pulse rate not the laser light frequency.
His phototransistor can detect on/off.
Dwight

So,

I would like just send lettre "a" with laser... How do I do ?

Thanks for your reponses Yoann

I would like just send lettre "a" with laser... How do I do ?

First learn to send a 1 or a 0. Two different laser modulation frequencies will work, if you can detect them reliably. Then compose the "a" from a series of 1's and 0's.

Laser Communication Instructable