This deluxe solar-powered light uses a battery and solar cells salvaged from a solar lamp with a four-cell battery (4.8 V nominal terminal voltage).
The circuit can operate from any DC voltage around this value and its current consumption, at 20 mA, is low. This means that the battery can give up to five days of operation. The circuit consists of an Atmel ATtiny microcontroller which drives a red, a green and a blue LED directly from three port pins. Series resistors are of course included limiting the LED current. The microcontroller drives the LEDs in sequence to produce an RGB running light effect. The microcontroller is also responsible for ensuring that the light automatically switches on when it gets dark and off when it is light. The light sensor is made from one of the solar cells from a broken solar lamp (it is more common for the battery to fail rather than the solar cells).
The power output of this cell is not important, as the microcontroller only measures its output voltage using its internal A/D converter connected to pin PB4. The project is ideal for beginners, as a ready-programmed microcontroller is available from the Elektor Shop (order code 100581-41). The author developed the firmware using Flowcode. Source and hex files for the firmware are available for free download from the project pages on the Elektor website at