Silly tinkering: a battery light.

What's that then? A battery come alive? A tiny robot? No, nothing that sophisticated. It is literally a battery light.

I found a bicycle's broken headlight on the street and salvaged the circuit board with the LEDs, the switch, a capacitor, and a bare chip under some white resin. Salvaging electronics is an old habit from the times I couldn't afford new parts.

It entered my mind that the PCB would fit snugly in the outer shell of a 9V block battery, with the LEDs on the top on the side, and the switch on the back end. No idea why I thought of this.

Hm.

Anyway, I added a 7805 to get the voltage down and put the PCB in the casing. I then connected the power leads to the former battery's contacts and filled the thing with a transparent pourable resin through the holes I drilled to let the light out. The resin serves as ballast and light conductor.

How to connect power to it was rather obvious, and there it was; very portable, and battery change doesn't get much easier, as long as you make sure you don't throw away the LED bit by mistake and connect the old battery to the fresh one. This will generate heat, not light, and may explode one or both batteries.

The LEDs do pull quite a bit of current; lowering the voltage across the LEDs and using a switching regulator would help, but I couldn't be bothered as this is only a gimmick.

Is it entirely useless? No, it makes people laugh.