Many times. I used the bicycle in the night and I dont have a lights!. So i decided a make a circuit that blink leds with few components and also very easy.

I also want the light, once installed, to be invisible and the back part of the seat offered a small space

Step 1: Choose the Retroreflector

I have 2 retroreflectores so I decided to use the biggest one that allows me to leave the pcb embedded and it is also red!

Step 2: The Circuit and Materials

since my goal was to use few components, use a ne555 ic as a hysteretic oscillator with which I achieve approximately 7 Hz. I used a 555 ic because works with low voltages like those of a li-ion battery.

I used the following materials:

ne555 smd
1 10k resistor 0603
1 10uF 6.3v capacitor
5 red led 0805 smd
5 220 resistor 0805
1 old battery from smartphone
1 small pcb 1x2.4 in

Step 3: Make the PCB and Connect Wires

I had never made a circuit with smd components, first soldered the LEDs and their resistors and then the ne555 ic, the 10k resistor and the 10uf capacitor.

Finally, solder wire to the pcb.

Step 4: Solder Connectors and Works?

solder some connectors to the wires of the battery and the pcb.
just need to close the circuit, will it work?

Step 5: It Works!

it works! :D

Step 6: Install in the Seat

just remain install all it, the pcb and the battery.

the pcb hold it at pressure by the retroreflector.

the battery is hold it with 2 zip ties to the back of the seat

Step 7: All Done!

the led light finished and running in the bicycle.

Step 8: Final Note

I did not use any switch so when I do not use it, I disconnect. But it would be a good idea to place a switch to avoid connecting it backwards and damaging it.

The pcb in principle I did it with a marker, but then I made a pcb in eagle that is seen in step 2, here is