It's a LED light originally conceived as an accesory for cyclists, but it could be used for any purpose. The frequency at which it blinks depends on the resistors and capacitors used. It can be calculated using this calculator for 555 Astable Circuits.
In the end we settled with the following values that set the frequency to 1.215 Hz or roughly 823ms.
R1= 100 ohm
R2= 100 kohm
R3 and R4= 220 ohm
C1= 2.2 µF
C2= 10 nF
1 Wazzabi LED Light PCB (PDF available)
6 Red LEDs
1 555 Timer Integrated Circuit
1 On/off switch
1 9v Battery
1 9v Battery connector
2 short cables (5cm each)
This part is up to your imagination. We used a transparent paper clip case that fit perfectly but a hand lotion jar could work too.
Velcro tape (20 cm)
Nail or metalic piece for heating and perforating plastic
During this instructable you'll see a 4,7 kohm resistor instead of the 100 kohm we finally settled with. This was a change we did at the last moment and we couldn't reshoot the photos. Just take the 4.7 kohm resistor as if it was a 100 kohm one.