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The aim of this project was to create a simple solar power light. I wanted to create a slightly different version than the ones you usually see for sale, and so, instead of enclosing the LED in a conventional enclosure, I bought some perspex and drilled a hole into the base of it. This allows the LED to shine from inside the tube, which causes the entire tube to appear as if it's glowing, instead of jus the bulb. This is based on the principle of total internal reflection, the same concept that allows light to flow through fiber optic cables.
I am using 4 1V solar panels, for a total of 4 volts in optimum conditions. These charge two 1.2V batteries connected in series, giving 2.4v power. For the logic, I am using a low-power version of the Attiny85, designed to operate on just 1.8V. This is probably more processing power than I need for such a simple project, but I am familliar with the ATiny chips, so I thought I'd use what I knew.
This is connected to an RGB LED, which is programmed to slowly cycle through all of the available colours over time.
The solar panel is also connected to one of the Attiny's analog input pins, which measures it's voltage. When the voltage drops below a certain threshold, the light automatically switches on, and switches back off again when the voltage increases.
The solar panel is connected to the batteries via a diode, to prevent backfeeding from the batteries to the panels when the voltage is low.
I was originally going to waterproof this and use it outside, but I decide dnot to, so I attached some perspex onto the base of the light to act as an indoor stand.
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