Using a sound source to drive an LED fader circuit...

joevennix · Post by **joevennix** » Wed Mar 01, 2006 8:58 pm

So I want to use a headphone jack to drive one (perhaps two or three in parallel even) LED so that it fades with the music. I was thinking I could combine L and R audio, then use a transistor and a few button cells to amplify the sound source. The output of the transistor would be regulated to the level sufficient for the LED(s) by a trimmer pot, and then the LED's would fade on and off to the music. Would this work?
Thanks...

daguuy · Post by **daguuy** » Wed Mar 01, 2006 9:10 pm

so you want an LED to light up when music plays and turn off when the sounds turns off? i'll make a diagram for it, i think it's pretty simple

joevennix · Post by **joevennix** » Wed Mar 01, 2006 9:21 pm

No... I was actually thinking more along the lines of using a headphone output to control an IR LED so the Mp3 player could be used as a remote, like that product, Total Remote, that Griffin released a while back. I believe this was posted on Engadget a while back. Anyway, the output of the headphone jack itself is not enough to drive the LED, so I would have to use an amp circuit to inject power into the audio signal so there would be enough to light the LED, or I would have to use a capacitor in front of the signal, and add a long, loud bit to the front of the signal, giving it enough time to charge the capacitor. This would involve finding the correct value capacitor, and I don't know how/want to do that. So, I took the transistor approach, and I'm pretty sure it would work, at the cost of the case being a little bigger, and batteries being used.

loup · Post by **loup** » Wed Mar 01, 2006 11:10 pm

they did the same thing in episode 6 of hak.5 using a laser pointer. They've got step-by-step instructions in the show

joevennix · Post by **joevennix** » Thu Mar 02, 2006 2:34 pm

No... in Hak.5 they build an audio transmitter. I want to build a DIY Pocket Remote. It's a device that lets you use any device with an audio output as an IR remote.

Radon199 · Post by **Radon199** » Thu Mar 02, 2006 3:03 pm

Ok so you want to build a remote control that uses an audio jack? For example like plug this thing into a Mp3 player and then when you hit diffrent buttons diffrent things happen?

Well thats not posible with a stock mp3 player. First of all the key presses arn't sent out through the headphone jack, just the music. What you really want is to find out the fequency that your TV uses for say, the power button. Then you make a mp3 that plays that frequency called "On/Off". then when you want to turn your tv off, you point your TV and play the mp3 "On/Off".

This is the way the Total Remote works, It learns the diffrent functions for your device and then creates an interface for it on your PDA (and it only works on a PDA, not any other device). Then when you hit a function on the PDA it plays a sound and thats makes the IR LEDs do their stuff.

In the end the point i'm trying to make is it's nearly imposible without someway to read the wavelangth for your devices remote.

Corscaria · Post by **Corscaria** » Thu Mar 02, 2006 6:38 pm

the mp3 compression would likely result in a nearly empty file aswell, as "inaudiable" sounds are dropped as another way of minimizing filesize

joevennix · Post by **joevennix** » Fri Mar 03, 2006 11:22 pm

Okay, here's what's going on...
A Griffin Total Remote is a cute little add-on device originally meant to turn your pocket PC into one of those really cool but uber expensive LCD remotes you see at Best Buy.
To use a Pocket PC as a remote, it attaches to the microphone input jack of your Pocket PC, and uses an IR receiver or phototransistor or something of the like as a "IR microphone." Then, the microphone records the IR waves (I/O) emitted by a remote control you aim at it. You then take the exported sound file and run it through the headphone jack of your Pocket PC out into the Total Remote Adapter, which amplifies the signal so it is outputted (sp?) from the Adapter, and the TV or whatever turns on.
What I want to do is build one of these devices myself. Now, the recording part is not that hard, as it just consists of recording using a IR phototransistor hooked up to the audio inputs on your computer. It is the playing back through the LED's that is hard. The signal coming from the headphone jack alone is not enough voltage to drive the IR LED's. So, I figured I'd make a little circuit, and after a little research, I figured I might just adapt this guy's circuit for my need. It would be enclosed in a round BIC pen case or something cylindrical of the like, would include two 1.5V button batteries to amplify the signal, and would have a headphone jack sticking out of the bottom, which you plug into the Mp3 player.
I just wanted to know if this idea sounded reasonable before I go out and spend money...

loup · Post by **loup** » Fri Mar 03, 2006 11:35 pm

you would most likely have to "record" the signal using some lossless codec, like wav, using a lossy codec like mp3 wouldn't work. As far as amplifying the signal goes, then a transistor, like you suggested, is probably your best bet. As far as whether or not it will work, in principal, it should, in practice... well, try it out.

The only one thing that I can think of is that it seems that it would be kind of difficult to use unless you were loading your own custon firmware onto the mp3 player. Otherwise you're going to have to scroll through your possible commands, and then select the one you want. At least on the ones that I've seen for a Pocket PC or Palm there are buttons to press on the screen.

joevennix · Post by **joevennix** » Fri Mar 03, 2006 11:52 pm

Yeah, I was going to use .wav to record, although honestly, the only reason behind it would be that this is the format the Total Remote software used. My idea is to just name each file for its respective function (e.g. Power, Channel Up, Channel Down, etc.), and then just scoll through them to get to that file. If I used a Pocket PC I could probably assign a button for each file, but for an iPod, I don't know...

joelanders · Post by **joelanders** » Sat Mar 04, 2006 12:39 am

http://features.engadget.com/2004/07/27 ... e-control/
That's the Griffin one.

vb_master · Post by **vb_master** » Sat Mar 04, 2006 12:34 pm

You want to hook up an LED to fade to music? You would probably have to use a PIC or something to analyze the music volume to fade the LED.