We were asked to provide a 60m long length of pedal powered fairy lights for Edinburgh based design group Here and Now They were running an event in a disused railway tunnel and wanted a spectacular interactive lighting installation.

We created a system using WS2801 addressable l.e.d.s with an arduino reading the voltage produced from a bike generator. As an overvoltage protection we employed a zener diode driving a TIP 122 darlington array as per this circuit.

60m is a very long way to try and send the 5V needed by the l.e.d.s. Since each bulb actually has three l.e.d.s in it for the red green and blue colours as the 5V drops the colour will be red shifted since the blue and green l.e.d.s require a higher voltage to run than the red. Although the effect is pretty it’s not ideal when you want a long string of white pixels – thankfully the WS2801 strips can receive power from either end. In the end we sent a cable parallel to the lights carrying the “high” voltage generator output then had 5V buck regulators at the midpoint and end of the string to inject power to the bulbs.

Here are some great photos by Jenny from Here and Now