My first circuit is a fun and easy to assemble Do it Yourself kit. It combines some of the most common electronic components (such as LEDs, resistors, capacitors, transistors etc.) with others that are rather interesting like the photo-resistor.

From a functional point of view it is a so-called joule thief or vampire torch that only actives in the dark. Specifically, LEDs need 3V to light up but the circuit is powered using only a 1.5V battery. However, when the photo-resistor detects low levels of light intensity the LEDs light up. How is that possible? The circuit has a voltage booster area that increases the voltage to nearly 6V so that it can power both LEDs in series. It does it through an oscillatory behaviour that fills the capacitor with voltage. Further, when the capacitor is charged the transistor comes into play as it releases all the voltage to the LEDs all at once. This process is iterated until the battery is fully discharged. This also means that the lights are not on all the time, but it all happens so fast that it is not visible to the naked eye.

The kit can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead").