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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I recently tried to make an IR music transmitter using but without the mosfet, or the flyback transformer, instead replaced with a 100 ohm resistor and an IR LED.
As for the receiver side, I used a black phototransistor (yes the matching wavelength) and hooked it up to a speaker. It worked, but it was really really quiet. As far as amplifying, I tried using a transistor, a totem pole, a mosfet gate driver, nothing works. As for using a plain mosfet, the IR phototransistor can't charge up the gate fast enough, and thus suffers a lot above human hearing frequency. Looking at the signal from the 555 timer, it's a relatively clean square wave with the audio modulation showing up as a jiggle in the square wave (as it is supposed to work).
Looking at the phototransistor side, however, the square wave is a LOT smaller, so much to the point where it's enough to power headphones, barely. Using a regular speaker the sound from it is hearable, but I need an easy way to amplify it well enough so it's nice and relatively loud.
Any ideas, other than the ones I've tried? It's a square wave, meaning no DC blocking caps otherwise the signal won't get through. I think I managed to fry two of my phototransistors in the process, heh. I need to order some more.
I've also tried using an LM386 with a schematic provided, the chip just heat up, a lot, and nothing was output from the speaker. I tried it several times over to no avail.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Analog opto-isolators commonly used in audio mixing consoles use a CdS photocell rather than a photo transistor. Old ones used miniature incandescent lamps but modern types have visible red LEDs.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Inducktion wrote ...
I recently tried to make an IR music transmitter using but without the mosfet, or the flyback transformer, instead replaced with a 100 ohm resistor and an IR LED.
I believe that there are much simpler ways to modulate the IR diode. That 555 puts out a high frequency square wave, and the audio probably PWM's it. That's how many simple plasma tweeters work. But really all you need is a simple audio amp chip which feeds the diode, causing it to be modulated by the audio source. You need to biase the diode so that it's always slightly on to prevent distortion.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Xray wrote ...
Inducktion wrote ...
I recently tried to make an IR music transmitter using but without the mosfet, or the flyback transformer, instead replaced with a 100 ohm resistor and an IR LED.
I believe that there are much simpler ways to modulate the IR diode. That 555 puts out a high frequency square wave, and the audio probably PWM's it. That's how many simple plasma tweeters work. But really all you need is a simple audio amp chip which feeds the diode, causing it to be modulated by the audio source. You need to biase the diode so that it's always slightly on to prevent distortion.
What would be a good audio amp chip to use? LM386? I think I killed my last one, unfortunately.
I hope it'll work decently enough, sound quality wise. I'll give it a shot and see how it goes.
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IR Transmitter for Music
