Dancing Lights




About: I'm Chandra Sekhar, and I live in India. I am interested in electronics, and building small one-off circuits around tiny chips (the electronic kind).

In response to music. Use a LED light removed from a pen, lighter or similiar device and a few other components to build it. No soldering involved. This is a simplified version of the blinking LEDs instructable posted here earlier. I shall try to elaborately describe each step so that a person with little experience can successfully build one.

The emphasis shall be on the methods of wiring and testing a simple circuit. The product of this instructable is not the blinking light you build - it is the knowledge that you gain as you build this extremely simple circuit, with materials that are commonly available, with simple tools and very little specialised skills.

Step 1: Take the Lamp Apart

Parts: Now that many gadgets come with an LED torch (flashlight) built in, it's easy to just buy one and take apart for the batteries and LED. You have to liberate the torch part from the pen, cigarette lighter or keychain or whatever. You should get three button cells, one LED and some sort of switch for completing the circuit.

The picture shows a pen with built in LED flashlight.

Step 2: Three Button Cells

The LED torch (flashlight) consists of three button cells and an LED.

The three button cells are visible in this picture.

Step 3: And an LED

The LED is inside the white plastic sleeve in this picture.

Step 4: Battery Holder, LED and Switch

These three components form a module. The switch is a springy piece of metal which makes contact with one leg of the LED when the button is pressed.

Step 5: The Switch

Here is a closeup shot of that switch.

The second picture is that of a similiar module removed from an empty cigarette lighter tossed in my path by an unknown benevolent wellwisher. Many thanks to that magnanimous person.

Step 6: Connect Wires

Connect two wires across that switch. The movie shows how you can test it.

The idea is that you connect an electronic switch to these wires and connect the music to it so that it closes in time with the beat of the music.

Then you will have a white lamp which flashes in time to music.

Step 7: Making Connections: Strip

You have to know how you can reliably connect components together using wire. This is an essential skill you need to acquire.

First, strip the insulation off the end of the wire. Cut the covering without nicking the wires inside. This takes some practice, and the best method I have found useful is to scribe a line around the insulation with a very sharp blade. The end can then be pulled off.

Trying to cut entirely through the insulation usually scratches the wires inside as well, leaving them fragile. Subsequent operations will cause the wires to break at this point, and you will have to do the stripping again. Leave plenty of slack in the wires in your early projects in order to allow for this sort of thing.

Step 8: Making Connections: Twist

If you are using stranded wire, ie, wire that consists of a number of small wires bunched together inside a plastic covering, the previous operation will have you looking at something that looks like the business end of a witch's broom about to take off into the blue yonder.

So twist them. Hold the frayed end between thumb and forefinger of one hand, and rotate the (larger) part of the wire with the other hand, and the strands will wrap themselves around themselves and present a very nice and respectable appearance, as in the picture.

Step 9: Making Connections: Join

Wrap the wire around the lead of the LED to make a neat joint. If you look at that picture again, one wire has been wrapped around the free lead of the LED, and the other wire has been jammed into the battery holder against the piece of metal serving as one pole of the switch.

I did that by pulling that metal piece out, and reinserting it with the wire wrapped around it.

Now when you touch the free ends of those wires together, the LED should light.

Next, we shall command a demon to sit there and touch the wires together in time to music.

Off we go, to get such a demon.

Step 10: Transistors

Here be Demons. A whole bunch of them.

This is a selection from my collection of transistors. Some of them might even be undamaged and work as new.

We shall use a transistor to switch on the LED according to the music. You can find transistors inside virtually every electronic gadget. Try to scrounge some really old gadgets because the transistors inside modern ones are likely to be too small to be seen without a microscope.

I shall use the BD135 from the collection in the picture. It is said to be a medium power silicon NPN transistor.

If you have to buy one, get the BD135 or an equivalent. Or try any transistor you pull off some electronic gadget. It has to be NPN, otherwise the type, make, size etc does not matter much.

Step 11: LED to Collector

Transistors have three terminals called the collector, emitter and base. These names originated long ago from the age when transistors were two sharp points pressed into a block of germanium.

For the BD135, the center lead is the collector. The other two are the base and collector, obviously. But I get confused, and have to refer to the datasheet to get the correct info.

If you are using the BD135 the pins are labelled in the picture. If you are using some other device try searching for the data on the web (use google).

The wire from the LED has to connect to the collector of the transistor, and is here shown stripped in readiness for connecting.

Step 12: Battery Negative to Emitter

The small exposed face of the button cell is its negative terminal. It has to be connected to the emitter terminal of the transistor. That wire has been shown stripped prior to connecting it.

Step 13: The Wet Finger Test

When the collector and emitter of the transistor are connected in place of the switch, it can control the lighting of the LED. A small current into the base (the free terminal of the transistor in the picture) will cause a much larger current to flow through its collector, both currents sharing the emitter lead.

When the transistor has been connected up as in the picture, the LED must remain off. At least it should, if the transistor is not faulty and it has been connected the right way around.

Now bridging the collector and base leads of the transistor will cause the LED to light. This is the classic Wet Finger Test.

Watch the video. I am holding the battery positive (one lead of the LED) in one hand, and touching the base of the transistor with the other. When the base lead hits the wet part of my finger, the LED lights up.

Step 14: Connect to Emitter and Base

If you have successfully applied the wet finger test, the next step would be the conncections to apply the music signal.

The transistor will conduct, causing the LED to light, whenever the voltage on its base is more than about half a volt (500 millivolts) with respect to its emitter. We apply the music signal between the base and emitter of this transistor, so that the LED will light in sympathy with the music.

The picture shows two wires connected to the base and emitter of the transistor.

When you have finished this step, the base and collector will have one wire each wrapped around them. In complete contrast, the emitter lead will have two wires wrapped around it.

Step 15: Connect a Resistor

Next, we need a resistor. Anything between 47 ohms and 1,000 ohms will do, it is not that critical. A 470 ohm resistor was what I used, as shown in the picture.

If you open up an old portable radio most likely you will get a collection of them. Try a few, any one of them might work.

Depending upon the source of your audio (music) signal, this resistor might not even be required.

Step 16: Earphone Jack

Next, we need to have something that plugs into a music signal source. The plug end of a pair of stereo headphones will do. Get the plug off a pair of broken old headphones or earphones if you cannot find the plug by itself.

Step 17: Cut Ends and Strip

You need to get the signal off the plug. Cut the wires somewhere and strip them. This earphone lead from a pair of really cheap earphones had bare copper braid and an enamelled wire inside the plastic insulation.

If you get such a lead, scrape off the enamel with a sharp blade - use gentle pressure to avoid nicking the wire.

Step 18: The Project Is Complete.

Connect it up, and the project is complete. Here in the picture, I have used a length of wire between the circuit and the earphone lead, but that was just for convenience.

Insert the plug into your tape player, MP3 player or computer sound card and try playing some music. The LED will light up in time to music.

But then there is a problem - you can see the LED light, but you cannot hear the music play. Some powered speakers have a socket for the other speaker, and you might try plugging this into that.

The video shows my test of my prototype.



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    50 Discussions


    8 years ago on Introduction

    hey, can you please make a material list??? so i can see what i need to buy


    9 years ago on Step 10

    i have tip41c, can i make with it?


    hey big question if you connect the earphone jack on any music devise the music should mute and only listen on the earphones, right?, why in the video the music is still playing and the earphone jack is in the music devise in this case a pc?


    11 years ago on Step 10

    You got a lot of old stuff. Nice instructable! Thanks. If you could put a schematic draft, that would be even better.

    7 replies

    Reply 10 years ago on Introduction

    awesome job dude...i tried the flashing lights thingy with my iPod and the lights worked!!!


    Reply 10 years ago on Introduction

    hmmmm...you think the transistor might be able to amplify sound also?like from an iPod to a Speaker?


    Reply 10 years ago on Introduction

    me too, but only those drawn by hand and scanned or drawn on computer, but with a kind of anti alias, like blur...


    Reply 10 years ago on Introduction

    Depends on the LED voltage requirement, if you send through 4.5v to a 3v LED it will burn out relatively fast compared to if the voltage was regulated through a resistor.


    10 years ago on Introduction

    Hey man thats sweet but my led doesnt go too brighty i dunno y does i need an amp to make it verry bright?