Well, there are many instructables on making music reactive LEDs some using Adruino, while others using TIP31 transistor. I saw one using OP-AMP as well. Inspired by those I wanted to personalize my laptop with LEDs which would blink with the music I played through my laptop. The laptop I have is Acer Aspire V3-571G. However there is a catch. I had two options:
1. The LEDs will only blink when the line out is connected, i.e, no blinking while the music is coming from internal speakers.
2. The LEDs will blink only when the internal speakers are working and not when one external is connected.
Well I had to choose one from the above. If you want to have best of both worlds, well then you have to go for a switch arrangement where you will manually flip the switch as per your requirement. You will understand this better when you go through the instructable.
I chose the first point as in this case only had to open the trackpad part of my laptop to expose the audio jack and not the entire laptop.
Step 1: The Circuit
Circuit as you see is a very easy part of this instructable and you might be familiar with it. if you want to take audio out from your headphone jack, check out the voltage output of your headphone jack, it is few millivolts. Those who want take the audio out jack from the internal speakers, your output would be around 2.5 volts and you have to go with TIP 31 transistor only. Those taking output from headphone jack you have the choice between 2N222 and TIP 31. I used 2N222 as it is 5 times cheaper here in my place.
So we will be using NPN transistor as a switch. Here we can control the collector current,i.e, the current through LEDs via varying the base current thus controlling brightness of LEDs.
For the power source to LEDs I had no option other than to use 5V from USB port. What I found is it is only able to power max of 2 LEDs and that also resistor not needed. But from the safety point of view I used a 100 ohm resistor in series with the 2 LEDs connected in parallel. You can experiment with your resistor values till you get optimal brightness levels.
Set up the circuit on breadboard and experiment with your no of LEDs and resistor values. Get your creativity high and think about feasible methoda to put your LEDs into your Laptop case.
Step 2: The Connection
So you see setting up the circuit ain't a big deal, more difficult job is squeezing everything into your laptop without damaging it.
First thing is the soldering. Be extra carefull, one wrong move and you have to give your laptop to service center.
First and foremost job: Plan your wire arrangement or your laptop case would simply refuse to close.
Using multimeter find out the poitive and ground points for your audio jack and solder wires to them. and setup the circuit according to the circuit diagram.
Next thing is figuring out the USB port whose supply you will be taking. Carefully, Very Carefully solder one red for +ve and one black wire for-ve on USB port without damaging any other IC, resistor, capacitor on board. If you have, till this step, done it carefully and strong enough, well pat your back because these two things are the hardest part of this instructable.
Step 3: Connect LEDs
Add the LEDs according to your creativity. I added them at the bottom, I think it looks cool.
Keep in mind that in future you may need to open up this laptop for some service repairs, so set up the LEDs in such a way that whatever the circumstance, you can take off the LED circuit safely without destroying it.
One last point: It seems that LEDs work fine when an external speaker is connected having its own amplifier. However these LEDs fail to work when unpowered headphones are connected. I don't know the exact reason may be its because headphones become shunted and full current goes through the headphone and not the LEDs.