Glue stck torch

Posted on Feb 4, 2014

This is a rather old project I`ve done around 2005 but was not published on my website until now. The idea of building a torch using a glue stick came to my mind when I realized that an AA battery fits perfectly into the glue stick`s plastic case. To make a complete battery holder there is also the need to make contacts for the positive and negati

Glue stck torch
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ve connections on the battery. The negative contact is made by cutting the plastic worm gear inside the stick, making a hole in it and passing a wire through the hole. The positive contact is made with a metal wire folded on top of the battery and kept in place using a spring. This makes it easy to replace the battery. The wire of the positive contact ends close to the black "knob" on the bottom, so that when turning the knob it makes contact with another wire, resulting in a switch to turn the torch on and off. I wanted to use two white LEDs as light source for this torch, but this turned out to be a problem because a white LED requires ~3. 6V to operate, while an AA battery is only 1. 5V. So I had to come up with some sort of switching step-up circuit to provide 3. 6V (or 7. 2V if wiring the LEDs in series) from an input voltage that varies from 1. 5V down to less than 1V (because battery voltage decreases as the battery discharges). And the circuit needed to be small enough to fit into the tiny space available into the black knob of the glue stick. If the base of the transistor is kept at 0V Vout is just Vin-0. 7 (the voltage drop of D1) because the inductor acts as a wire. But if a square wave is applied to the base of the transistor, it acts as a switch opening and closing. When the transistor is closed the inductor is connected to Vin and ground, and the current in it increases linearly with time, while when the...

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