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
The picture shows a pen with built in LED flashlight.
Step 2: Three button cells
The three button cells are visible in this picture.
Step 4: Battery holder, LED and switch
Step 5: The 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
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
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
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
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
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
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
Step 13: The wet finger test
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
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
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
Step 17: Cut ends and strip
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.
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.