This is an LED decade flasher circuit.

The circuit cycles through ten stages. It runs off 9V batteries and is enclosed in clear plastic to make it water resistant and make it fresh looking.

It can be attached to a bike, a messenger bag, a hat, lingerie, a back pack, anything you want.

If you've never done anything with a 555 timer before, this is a good circuit to start with!

To build this circuit, you need breadboarding skills, soldering skills, and to finish it in plastic, you need to sew or have someone sew it for you.

How does it work?

A 555 chip is used to make a clock that sets the beat for the HCF4017B decade counter.
The clock speed is adjusted by changing the values of the resistor and capacitor.
Bigger means a slower pulse time, smaller values make faster pulses.

The 10 outputs of the HCF4017B are connected to the bases of 10 NPN transistors (BC547s, or 2N3904s, both can work).
Each transistor drives 4x 500mcd LEDs at 9 volts.
This kind of LED is more efficient, running brighter.
If you use less efficient ones, then you can only load about 2 LEDs.

Step 1: Parts List

All of the parts are easy to get hold of and inexpensive.

A few tips:
A pair of helping hands is vital, especially when you solder the LED array.
And heat shrink will protect you circuit, not only protecting it from short circuiting, but by keeping supplementing the soldered joints by providing a strong mechanical bond.
Use colours to code your wires. Red, black, pretty obvious. Green for signal. White for transistor to chip. It might sound a bit obvious, but I never used to do it this way, only after tech that I started forming this habit.

Tools
Helping hands (really useful! I couldn't have done it without these...)
Heat shrink tubing (at least 2km, in all sizes)
Side cutters, wire strippers, nail clippers.
Soldering iron
Dust/Gas mask

Parts
Black, red, white and green hookup wire.
555 timer chip
HCF4017B decade counter
1x 8 pin IC socket
1x 16 pin IC socket
10x 3904 or BC547 NPN transistors
40x 500mcd orange LEDS
1x green LED
1x 1000 ohm resistor
1x 4700ohm resistor
1x 10 micro Farad polarized capacitor
1x DPDT power switch
1x 9v PP3 battery clip
1 set of 2-way sockets and connectors, any type.

Packaging
Clear plastic material (go to a fabric shop)
Clear plastic tubing, 0,5mm (go to a hardware store)
Velcro strips (also a fabric shop)

What? Only one resistor needed? I'm not going to add any with the leds? That's right, and I don't need to. Four in row at 9v, and pulsed 9v also won't have too much risk of overheating and burning out.

Here are the data sheets for the two chips:
http://pdf1.alldatasheet.com/datasheet-pdf/view/8979/NSC/LM555.html
http://pdf1.alldatasheet.com/datasheet-pdf/view/133628/ETC/HCC/HCF4017B.html

Step 2: Testing the Circuit

555 timer clock

Assemble the circuit on a breadboard, starting with the 555 timer part.

(See the diagram)

To make sure it works, connect an LED to pin 3, to ground.
If it's working, the LED will pulse.

Sequencer

(See the diagram)

The connections for the outputs of the chip are a bit fiddly, and go in this order:
Pin 3 - #1
Pin 2 - #2
Pin 4 - #3
Pin 7 - #4
Pin 10 - #5
Pin 1 - #6
Pin 5 - #7
Pin 6 - #8
Pin 9 - #9
Pin 11 - #10

Test everything and get it running.
If any of the LED parts won't light up, check and see that all the LEDs are connected the right way round.
If the LEDs light up in a semi-random order, you've connected it to the wrong pins.
Other than that, nothing else should go wrong.

Step 3: 555 Timer

Now you'll start soldering the parts to get them ready to go mobile!

Starting with the 555 timer.
The better at soldering you are, the more compact you can make the pieces.

When you're done, slot the chip into the holder, making sure its the right way round.

Step 4: LED/Transistor Array

You first need to combine a transistor with 4 LEDs.

Remember, I used 3904 transistors - you need to check which pin on the transistor you are using is base, collector, emmiter.

Make 10 of these combinations.

Solder the collectors to one common rail for the +9V. Solder a red wire to it for clarity.

Solder all the 0 volt ends to one common ground rail. Give it black wire.

The whole thing should be in a long rectangle shape.

Step 5: Assembly

Solder a loose red wire to pin 16 for the 9v connection.
Solder black wires from the 8th, to the 13th, to the 15th, to a loose black wire.

Remember to slip on heat shrink before you solder the wires together.

Now you solder the correct transistors to the correct pins of the 16 pin IC holder.
Make sure you have the orientation correct - you should have the diagram in front of you.

Slot the chip in, right way round.

Now you'll connect the clock.
Solder the ouput of the clock (green wire, pin 3) to the input of the counter chip (green wire, pin 14).
(See photo)

Solder the red wires together.
Solder the black wires together.
Slip some plastic tubing over them and terminate with the 2-way connector.
(See photo)

Check and see if it works by connecting the 9v battery.

Step 6: Power Switch

Remember the lil' green LED you saw earlier?
Solder it together with the 1k resistor and cover both legs with heatshrink.

(See photo)

Solder each of the battery connector leads to the common contacts of the switch, and solder the LED part parallel over the normally open contacts.

(See photo)

Solder a length of black wire to the negative normally open contact of the switch.
Solder a length of red wire to the positive side of the normally open contact.
Slip plastic tubing over the two lengths, and terminate the ends with 2-way socket.

(See Photo)

Step 7: Packaging

Connect the power socket and connector.
Switch the switch.
Feel the epilepsy.

Using the clear plastic, sew a tube big enough to fit over the entire circuit and array. Close up one end. Turn the tube inside out so the hem is on the inside.
Slip the circuit inside, and sew it closed with the tubed power cable sticking out.
(See photo)

To square the battery and switch away, I added clear heatshrink to the one end and used a length of bicycle tubing to hold it to the battery.

To make the pack able to be attached to anything, glue 3 strips of velcro to the BACK of the pack. Hot glue works surprisingly well, but I'm not sure howit would hold up under cold weather.

That's my instructable. Hope you like!

And if there's anything you don't understand, or anything that wasn't so clear, please feel free to ask.