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View Full Version : What do I need to do this?



Kayin
04-17-2012, 10:03 PM
All right, so I have a fair few of the parts I need. I have the speakers I need for my PC front, I have a Jupiter Electronics voice box, and I have a lot of wire. What I need to do is to set up the speakers in such a way that the voice box lights up when they play sound. I can do the individual sound card set ups as well as the PC automation stuff, but the signal from my line out isn't strong enough to trip my voice box. Do I need an amp, will it hurt my laptop speakers (literally from a laptop, Toshiba Satellite, brand new machine destroyed by someone's stupidity) and if so, where to find it? I can handle solder it yourself stuff just fine. Just need to know what I need here. For comparison purposes, the voice box I have is normally run by a car stereo system. So I'm guessing that it needs some amping. The maker said that he'd had luck from people off their PC sub, but KITT's voice is rather high. The front setup will only be used to play voice clips, so there won't be a sub at all.

Help me Obi-Wan Kenobi, you're my only hope (in a manner of speaking.)

TLHarrell
04-18-2012, 01:05 AM
You want these:
http://www.national.com/mpf/LM/LM3914.html

Konrad
04-24-2012, 11:21 AM
Just use a generic transistor amp circuit (http://www.daycounter.com/Calculators/Transistor-Bias/NPN-Transistor-Bias-Calculator.phtml) with the correct voltage bias for the speakers. If Toshiba Satellite uses standard mini 5V/8Ω magnetic loudspeakers they'll require a bit of signal drive (~3W for the pair) and be able to tolerate momentary overwattage without being damaged/derated. If they're piezo speakers then you'll need to be a little more careful not to overload them. Otherwise, just fiddle with resistor and diode values until you get reasonable maximum volume/light level.

Another good option would be to use an audio amp circuit based around some kind of LM386 (http://www.ti.com/product/lm386) part. Gain is respectable and distortion isn't very relevant in this application.

These sorts of little parts will probably outlast the LEDs and generate inconsequential heat. You could use an electromechanical relay instead, but it's less efficient, fugly, probably won't last as long, and the constant click-click switching on a direct-audio signal would probably be really annoying.

I realize you want lights, not sound ... but unless you can adjust the sensitivity on whatever sensor part your LED driver circuit uses, it's probably easiest to just feed it exactly the sort of audio intensity it was built to detect.

TLHarrell
04-25-2012, 12:54 PM
Found the post I had seen about this in my bookmarks at work.

http://www.adafruit.com/blog/2012/04/13/partfinder-friday-the-lm3914-is-an-analog-input-led-driver/

Crimson13
04-25-2012, 05:19 PM
There's also this: http://www.sparkfun.com/products/10468

It outputs DC so it might give the effect you're looking for.

TLHarrell
04-25-2012, 07:23 PM
LOL! Take a look right below the product photo thumbnails. See the link for ASCII Version? Click on it. Awesome.

Kayin
04-26-2012, 04:11 AM
The voice box has an LM3915M on board. I need to boost the input power to it without ruining my tiny but rather powerful speakers.

I'm starting to wonder if a DIY headphone amp wouldn't work.

TLHarrell
04-26-2012, 02:15 PM
Split the audio signal up and send part of it through a transistor to the voice box trigger. Apply voltage to the switched side of the transistor as needed to get to your trigger voltage.

Kayin
04-26-2012, 04:28 PM
That I can do. Now, to draw up the board I'll need for all this stuff...