Thank you for taking the time to explore the avrprojects website. Here you can find projects about AVR 8-bit microcontrollers. We hope you´ll find these pages both educational as inspiring.
A photocell or photo resistor is a Light Dependent Resistors (LDR). LDR's are sensors that detect light. They are small, inexpensive, low-power, easy to use and don't wear out.
A VU meter indicates the Volume Unit, mostly of audio equipment. A VU meter is used to get a sense of the loudness of the signal. A VU meter can also be used in any other equipment to measure intensity levels.
The HDSP2111 is a very nice LED display, the can show 8 alphanumeric characters in a 5 x 7 dot matrix, and are all packaged in a standard 15.24 mm (0.6 inch) 28 pin DIP. The onboard CMOS IC has 128 ASCII characters which are permanently stored in ROM.