Picture of Sound reactive 2.1 audio amplifier (flashy ipod dock)
2012-05-04 09.26.43.jpg
This is my version of the LED boxs that i have seen on this site. This formed the final part of my degree course as a trainee Secondary Design Technology Teacher.

Its pretty simple. I took the flashing circuit for an led box and built it into a ready made 2.1 system, then made a new housing for it.

Have a look here for a video of the finished product:http://youtu.be/0kvhXYVkGGU

Credit to motadacruz for his instructable as it was his awesome guide that got me doing this one, anyway have a look at this for the circuit but forget about the stereo cable as we are going to hard wire this into our audio circuit

The Circuit to control the LEDs consists of a NPN transistor (everyone recommends tip31 but i used tip 121 as thats what we had in the electronics cupboard). The base (left leg) connects to the signal source i.e the positive wire on the speaker. The collector (middle leg) connects to the first negative leg in the chain of LEDs (the amount of LEDs you can run depends on your voltage) the emitter connects to the 0v rail on your power supply. Thats it. there is no need to ground the negative audio signal like everyone else states.

evilpuppy2 years ago
hfisher33 years ago
Hi sorry just one question........... the LED strip also supply's the power ( or whatever you nerd call it ;) ) to the + port thing of the speaker then u just wire the - as normal ...? if not ...please explain ? and whysand and drill 3 holes in the amplifier ? is that to attach the LED strip to also?
woody2k (author)  hfisher33 years ago
I'll try and use non nerd speak for this. The speaker is wired as normal. There is a wire from the + terminal of the speaker as the input signal for the leds. The wires from the circuit board supply the power for the leds. When the signal is high ( the speaker makes a noise) the transistor (thing the leds are wired too) allows the full voltage from the circuit board to light the leds. That's it. The transistor is a gate. when a small voltage is applied to it (from the speaker) it allows the full voltage to flow through it ( and light the leds)
Ok so im about to start the LED string..... where do i put the resistor u mentioned to protect LEDS? ( not infront of the transistor or it would defeat the purpose of it)? So on your photo u have a Green and Black wire, one goes onto the + of the speaker and the other one goes ?
" Sand down the rails to expose the copper before drilling holes to run your power leads from (i drilled 3 holes so i could have lights on the left, right and bass)"? I thought the power was alrady supplied to the leds from the sire to the + speaker port.

Sorry if i sound thick, but im not! haha im a sports scientist and this is all new to me, ive even purchased the same speaker system ! the speedlink so i can compare it to your diagrams !
woody2k (author)  hfisher33 years ago
Have a look at the diagram I point to at the start of the instructions. The resistor goes before the led string. It stops too much voltage flowing through them and blowing them. The lead to the speaker is the signal not the power. The speaker only does about 0.25 volts. That's why we use a transistor, this allows a small signal voltage to trigger the larger voltage.and make the leds flash. So 1 lead to the speaker terminal (must be positive) 1 wire to the positive rail and one to ground. That's it. Make sure you view that diagram. Also post me a link to your finished piece
haha ohh !!! The rails are the spikes on the bottom of the transistor!!!? If thats correct, why did u drill 3 holes on ur like mother board thing? i have not drilled holes...yet.I will send you a post.

Thanks again !
woody2k (author)  hfisher33 years ago
Right let's start again. Read the whole thing. The board thing provides the voltage for.the leds. I drilled them so I can put wires in and solder them. That is what we call a positive or +v rail. The other holes are the negative rail or 0v. Read the whole post then ask me again.
The base (left leg) connects to the signal source i.e the positive wire on the speaker. The collector (middle leg) connects to the first negative leg in the chain of LEDs (the amount of LEDs you can run depends on your voltage) the emitter connects to the 0v rail on your power supply. :) so if i do 3 led strips 1 wire from each one goes to one of the 3 holes ? 1 strip goes to 1 hole....?
woody2k (author)  hfisher33 years ago
Right ok lets put this in less than Layman's terms. The transistor has three legs, a base a collector and an emitter. you have copied and pasted above the correct bit. If you look at my pics i drilled 6 holes. thats 3 in one part and 3 in another part. One part is the supply voltage (my +v) and the other is the ground (0v) so as it says above....
The base (left leg) connects to the signal source i.e the positive wire on the speaker. The collector (middle leg) connects to the first negative leg in the chain of LEDs and the emitter connects to the 0v rail on your power supply.

so one lot of LEDs connects to one hole in the +v one hole for the 0v and one of the speaker terminals. Just read the whole thing
omg i did not see the other 3 -.- sorry about that! makes more sence now! So LAST QUESTION then ill send u a post of my finnished product! Does it matter where i drill the 6 holes ? aslong as its not going through a component ...obvs?
woody2k (author)  hfisher33 years ago
Yes it matters. On an audio amplifier there is normally a positive and negative voltage. This increases the potential difference ( means there is a larger difference between +18v and -18v rather than +18v and 0v) if you drill the holes where I did you define have +18 v and 0v. Anywhere else on the board you could have a totally different voltage. ALSO MAKE SIRE YOU DO NOT TOUGH THE CONTACTS ACROSS THE BOTTOM OF EITHER OF THE LARGE CAPACITORS. the are used to turn the +18v current from the wall into dc current for the board. If you short out one of those (touch both pins at the same time) the capacitor will discharge and trust me that is about a hundred volts. That will hurt.
garren113 years ago
Deadmu5 great choice
amen to that
BeaSk8r1173 years ago
Ooh! This is awesome!
Also, the music choice = awesome.
tcop3 years ago
very nice!
It is obvious you have many skills (electronics,woodcrafting,painting etc)
Cool mod, would fit nicely to any living room
woody2k (author)  tcop3 years ago
Thanks, this project will be sitting nicely in my classroom in September
usbg3rd3 years ago
hi woody2k
nice project i have a suggestion that u can use transistors with a very high resistance at the base .. when u do this u will be able to use as many Led's as u can without dropping the sound of the amplifier or distorting it too... :)
btw keep up the good work....
woody2k (author)  usbg3rd3 years ago
The tip 121 transistor is a Darlington pair with a built in diode meaning that there is no feedback through the component and the signal is effectively amplified. I'm only running 3 LEDs off a transistor because they are in series, there is no problems with distortions whatsoever.
The LEDs on the bass tubes/ports are 2 series strings of 3 LEDs running off one transistor in parallel (6 LEDs in total)
bowlen1993 years ago
sorry my mistake (derp) you did buy it
bowlen1993 years ago
very cool. how the quality of the sound from the amp you built compared to say, a 12 V £30-£40 car stereo amp?
woody2k (author)  bowlen1993 years ago
The sound is actually better now than when it was in its original case. There is a larger space for the bass and main speakers and this gives a richer deeper sound. The video doesn't pick up the audio well and doesn't do it justice, as for the sound compared to a Car amp I'd say its comparable. The unit itself brand new cost about £30.00