Can I transmit audio through light using Optocoupler's working theory?

[Willen]

By connecting sound waves to LED (it will light according to sound waves) and receiving the transmitted sound light by using photo transistor or LDR or photo diode. Or any possibilities?

 

[Willen]

May be possible with fast responce LED- Infra Red LED with its suitable Tx and Rx.

 

[kubeek]

How far do you want to transmit? Basically if you want true optical connection, then I would use a setup similar to RONJA. But transmitting just the bare signal will likely lead to distortion and noise, so you would probably want to use some more complex things like FM modulation or going entirely digital.

 

[Nigel Goodwin]

Optical communication has been done for many decades, I even remember seeing one using a fluorescent tube a long time back in a magazine (60's, 70's or so?).

It certainly pre-dates transistors

 

[dr pepper]

There a guy that did this over miles with a neon tube.

Opto couplers can be used but the frequency response isnt linear so you'd need to encode the audio using something like pwm, or incorporate another identical opto coupler in part of the feedback loop for an op amp to give you appropriate equalization.

If its just an experiment or a school demo or quality doesnt really matter then that wouldnt be necessary.

When I was a kid I experimented sending data via car spotlights, very interesting.

 

[KeepItSimpleStupid]

Well, there are highly linear optocouplers: **broken link removed** with enough bandwidth.e.g. 200 kHz.

 

[MrAl]

Hi,

Light was used to transmit information at least as early as 1775 using lanterns
"One if by land two if sea"

The light output of an LED is roughly linear with current (not voltage) so you could start by driving the LED with a controlled current source. The current output of a solar cell (not the voltage) is roughly linear with light input, so you could use a solar cell as detector.

How far you can transmit depends partly on how good the devices you use are and what optics you use with them. A lens on transmitter and receiver will increase the transmit distance 10 fold or more. A modulated carrier will prevent room ambient lighting (which often has modulated intensity due to the power line frequency amplitude fluctuation) from interfering with the transmission.

Improvements of course would come with improved devices such as multiple transmit LED's or a laser, and possibly certain commercial receivers made for IR remote detection.

 

[ronv]

The problem I had when I tried the cheap and dirty route was the lack of the carrier as Mr. Al pointed out. Worked great in the dark but as Audioguru says it had Hummmmm with the room lights on.

 

[audioguru]

Light bulbs work at the mains frequency so they flicker on and off. Then they interfere (humm) with simple AM (amplitude modulation) audio IR communication.
But if the IR has a high frequency carrier then the mains flickering has no effect.
But modern compact fluorescent light bulbs work at about 38kHz and might cause interference.
Maybe use a higher carrier frequency and FM modulate it.

 

[Mr RB]

A quick google found this site;
www.modulatedlight.org

**broken link removed**

this page;
https://modulatedlight.org/Modulated_Light_DX/OpticalComms4Amateur79.html
has tons of good info.

 

[ronsimpson]

Can I transmit audio through light using Optocoupler's working theory?
By connecting sound waves to LED (it will light according to sound waves) and receiving the transmitted sound light by using photo transistor or LDR or photo diode. Or any possibilities?

The title mentions Optocoupler's where I assume the distance is 0.1 inch in the dark. If you bias the LED so 2mA is flowing all the time and then with analog audio modulate the current from 1 to 3mA you will get audio on the transistor side of the Optocoupler. Running the Optocoupler's in linear mode makes it pretty fast. There will be some distortion.

LDR

They are very slow. 100hz is about as fast as I got from a LDR.

photo diode

very fast!!! 100mhz Must see a strong signal.