I was enlightened about this Battery Less wonder. This is a boon for rural areas and an emergency tool which depend only on your will and your tendons. I found this bright flash of information when i was looking for supercap vendors.
Learn about Supercaps, dynamo and White LED
Richard J. Nelson on the LED Forever Flashlight. – The future of low power lighting is in the use of the Light Emitting Diode, LED. Sooner or later you will buy one or more LED lights or lamps. The two primary advantages of an LED light source is it’s efficient light generation (exceeding that of fluorescent lamps) and long life, typically 100,000 hours. That is 50 to 100 times more life than most of the bulbs in your house.
This is a Linear Dynamo LED Torch which uses a SuperCapacitor to store the energy. Easy to repair and maintain if necessary.
It uses no batteries and requires only the single LED included. You can even leave the flashlight unused in your car’s glove box for years and you’ll always get that all-important light when you need it most. Forever Flashlight lll pays for itself quickly by saving you the cost of batteries and bulbs.
I had gone to buy some long wires at a electrician shop, when a terminal box had to be tested, he used a continuity tester.
When i used to buy electrical parts in the past, they used a tester box, made of wood. This had a bulb and a tubelight starter and two long wires (230v AC). The Continuity tester would light up a 40w lamp. Now he had a LED based one, so i got one for myself.
All it had, was two small cells in a plastic box with a LED, i was just flashing the LED as it looked nice thru the transparent box, it failed. The LED had burnt, the battery used. This product was not for monkeying around.
Now i performed a tiny design upgrade, I used a extra-bright 3mm Red LED with a 47 ohm resistor. Now it is robust, at least for continuity. The battery life can be good only if you make quick checks.
More protection may be needed to avoid damage to LED when this tester is applied across a battery by mistake. LED can flash to save battery power, one SMD – LM339 can be used for flashing and a more efficient short-leakage detector. A small oscillator with a neon may be more efficient and bright. This can also double up as a hidden Live wire or Mains AC detector.
A single chip metal detector with a range of a few inches. This is useful for detecting nails or screws in walls and floors, or for locating buried mains cable.
This article describes a simple continuity tester, based on an ATtiny85 and a piezo buzzer, designed for checking circuit wiring, or tracing out the tracks on a PCB: