Like I'm sure most Instructable users I have a jun...err..future projects box and to find things in said box can be quite a challenge...

I needed a small flashlight that doesn't always need new batteries or needs hours to charge....and needs to be very rugged.

Supercapacitors to the rescue, with my current setup it plugs into a USB for less than 1 minute to a full charge for about 30 minutes of runtime.

Supplies

For my build I used:

4 Starcap 2.7V 5F capacitors

Male USB connector

2 Resistors 1ohm & 100ohm

1 Ultra high efficiency CREE 5mm White LED

1 Mercury switch

....Not necessary but I also etched a small PCB to hold the components.

Step 1: Keep It Together

I decided to make a small PCB on my CNC.

I start with a quick design on EasyEDA exported as a black and white image.

Then I take a photoresist copper board and engrave the image onto the board with my CNC equipped with a 3500mw 405NM laser. You don't need a lot of power it only takes about 50mw of power to expose the board. As you can see I created some sunglasses for my laser to reduce light spill from the laser module.

I run the engraving at about 500mm/min and at ~100mw power.

After that is finished I develop the board and etch it in a hydrogen peroxide and pool acid solution.

This is how I make all my PCB's and I'm very happy with the results.

Soldering the flashlight is easy:

USB goes through a resistor to limit the current to supercapacitors this protects your USB, I used a 1ohm resistor.

Two of the supercapacitors are first soldered in series to make a 5.4V 2.5F capacitor then in parallel so that we end up with a 5.4V 5F capacitor.

From the capacitors we have the mercury switch that turns the flashlight on when pointed downwards.

This goes to a 100ohm resistor and then to the LED.

USB->1ohm resistor->Supercapacitor->Mercury switch->100ohm resistor->LED