Introduction: Sound Reactive 2.1 Audio Amplifier (flashy Ipod Dock)

About: I am a Design Technology Teacher currently teaching Electronics but have trained / taught and studied everything under the D&T umbrella
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:

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.

Step 1: Getting the Circuit and Testing

So this is the build:

I chose a cheap 2.1 system, stripped it down and played with the circuit. Although this system was AC (i live in the UK) it had transformer and bridge rectifier to lower the voltage and produce DC current. A fiddle with the multimeter showed it produced 17V

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)

once you have run a power supply off the amplifier board and created your circuit you should get something like this:

(i have these LEDs in series and paralel in order to test but basically they are superbright Blue LEDs, they have a safe working voltagge of upto 5.5v       17/5.5 = 3.09 so i can have 3 LEDs in series and a protector resistor.

Now plan out how you want the lights and it will determine the design of your housing.
I  went for 3 lights around each speaker and flashing bass ports. The spacing of the volume and bass dials could bot be changed so I placed them in the middle of the housing.

To difuse the lights around the speakers i used acrylic rod, drilled at one end at 5mm to accept the LEDs and sanded at the other with 400 grit wet and dry to defuse the light. The bass tubes are acrylic tube drilled 5mm again to accept the LEDs but this time the lenses of the LEDs have been sanded away as i want the light to diffuse through the side of the led and not protrude into the tube.

My design looked like the last picture on this step:

Step 2: Creating the Housing

So the housing. i went with MDF as its easy to work and doesnt have any grain to worry about.

Decide of the size of your box, I cut lap joints into all my boards with a table router, this made sure it would stay square and add extra strength. i also added escape ports to the back panel so the audio from the main speakers did not rattle around and cause a noticeable delay. mark out holes for your switch, audio input (originally this was a twin RCA but I created a 3.5mm stereo jack instead) and powr cable

This takes a little time but its worth it to get a decent finish......about 5 days work)

1) Cut out your front panel, sand down and clean. i ran the holes through the router to profile them and give a better finish.. then cut your back panel.
2) Glue everything together (not your back panel) but put the back panel in to make sure it all snug and doesnt warp Clamp it and leave overnight
3) fill any gaps with car body filler (easy sand stuff not glass fibre). leave 20 mins to dry and then sand back till flat (i used 320 grit paper)
4) run it through the router to profile the corners (if you are going to)
5) give it a coat of white primer and leave overnight to dry (This makes it easier to see how much you have sanded off)
6) Fill any imperfections and seal the newly rounded edges with filler, again sand back.
7) when happy spray with highbuild primer and leave to dry
8) rub back with 400 grit paper till smooth. then repeat high build (leave again overnight) and sand

Now you are ready for the coating, I chose stone chip paint as it is cheap and provides an anti scuff / scratch finish. some people recommend truck bed spray but in the UK this is not readily available and so that means its expensive

make  sure you are happy with the finish as a final coat will show any imperfections up.

Spray a coat of stone chip. leave over night, spray again leave over night.

Next we are going to create the compartments for the audio to reverberate in....

Step 3: Creating the Compartments

Right, do all of this with your box face down an old towel, this will stop it getting too marked.

I separated both sides of the box and created a compartment for the Volume and Bass knobs to sit in. This takes some time and effort as it needs to be a tight fit so its doest move around with the vibrations later. Work out the best design for your circuit but make sure you have a space around your speakers in give it a better sound.

Once happy with that cur a board that will sit on-top of these divisions and seal them off, i chose to use the same 6mm mdf that the rest of the box had been made from, this should stop it vibrating. Again it must be a tight fit so take your time and do it properly.

Now i want my bass tubes to protrude through to the rear compartment as that is were the bass speaker will sit. so after i have worked out its position in-line with the front and cut the hole its time for a test. i also need the escape tubes for the left / right audio through the back so these will move through the centre division and out of the back panel. Taking into account the thickness of the lap joint these are marked out and drilled. again time for another check

The bass speaker is a little large so mine was mounted at an angle. to do this i cut away the piece that covers the volume control as this doesn't really matter anyway.

Right, lets get all the electronics in...

Step 4: Final Push (get the Circuit In)

Ok, this is the hardest bit.

Lets do it step by step.....

I wired up my LEDs and transistors earlier so i could just stuff everything in. Have a look at the first pic in this section. I made them all on flying leads as i really couldnt see the advantage of creating circuit boards for them. i have 3 circuits going in, 2 identicle ones for the Left / Right audio and then 1 transistor with 2 LED strings running off it for the bass tubes. dont forget to include protection resistors for this part of the circuit, you dont want the LEDs to pop after a week. i used 330Ohm

1) Firstly fix your speakers in place, then wire the signal input (Audio + on the speaker ) to the base leg of the transistor (the left one)

2) make sure you use either heat shrink or insulation tape on all your joints here, if something touches here its not going to work and you aren't going to fix it. i screwed my sransisrors to the inside casing to stop them vibrating and moving around.

3) push your LED diffuses into their positions around the speakers and then mount the LEDs into them. i suggest using a glue gun or superglue here to fix them in place and fix the wires down also.

4) Put your dividing cover in place and run all your wires through, at this point i sealed around the edges of the compartment with hot glue.

5) Wire the LEDs to the power output from the main board, (remember to do positive and negative)

6) at this point i fixed my volume control in its little compartment with araldite as the original threads were not long enough to poke through and wired my last transiistor circuit to the positive terminal of the bass speaker.

7) Make sure everything is wired up then mount your bass speaker. i created a mount to hold it at a 25 degree angle but thats your design.

8) put the bass tubes in and insert the LEDs. when happy again fix them with glue. look at the front ogf the housing to check the position of the bass tubes then glue them in place inside.

9) wire up the led string and run all the required cables through the back panel. This for me was the power. switch and audio input.

10 ) screw your main board down. transformer etc and glue the cables down to stop vibrations. 

11) Put the back on, and give it a test.

With mine the bass and left/right LEDs flicker at different rates as they have different inputs. as you turn the bass control down there is less signal so the lights go out, same with the volume.

I made the 3.5mm connection rather than using the twin RCA cables as this took up less space on the rear panel and everyone has a spare 3.5 to 3.5 cable now a days (they have green plugs at each end and come with your shiny new computer monitor)

Hope this has been of some use to you.

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