now looking for projects that allow students to consider sustainability, and, what better way to do this, than with a solar garden light. This project allows electronic construction, resistant materials, renewable energy and the study of designers, to be included in one scheme of work. This product is very similar to the solar garden lights that can be found in garden centres and hardware stores. During the day, a solar panel is used to charge up a rechargeable cell, and then at night, when the light level falls, the LED turns on allowing a path, step, or other feature to be illuminated. The soldering in the project is fairly simple as the circuit uses just 15 components and no ICs. Assuming students have practiced some soldering prior to assembling the board, any key stage 3 class, should find building it relatively straight forward. With the essential job of making the board complete, the rest of the scheme of work can be designed to cover as many areas as time allows. Students can either design an enclosure for the board to go in to, or, alternatively, if time is short, a large jar can be used to house the board. In this case, reuse / recycling can be added to the project. Renewable energy can be examined; just as solar, wind, hydro, or any other renewable energy sources could be studied. Maths can be included into the project by studying how long it takes to charge the battery. The electronics can be studied in more detail by looking at the components the circuit uses, such as LEDs, resistors, capacitors and transistors. A case study of product designers or inventors, like Trevor Baylis, who famously designed the wind up radio, could be included in the project ( The circuit diagram (above) shows how the components are connected up to make the solar garden light. The diode allows the battery to be charged during the day and prevents it from discharging through the solar cell at night. The transistor, Q1, turns the rest of the circuit on when it goes dark. Since the LED needs 3. 5 Volts, and the cell only delivers 1. 2 Volts, some extra circuitry is needed. This turns the LED on for a third of the time, but at 3 times the battery voltage, and, because this happens hundreds of times a second, the human eye thinks the LED is always on.