This circuit is a MIDI interface between drum pads and computer or hardware sequencer. Using this circuit you can hit pads with drumsticks and store the MIDI data in real time.This circuit is based around the PIC16C84 microcontroller which scans the inputs on RB0 to RB7 and when a high is detected the software transmits the equivalent note-on ( and then the MIDI note-off after a short delay) for the required drum sound on the MIDI output on RA0. source

This a simple circuit demonstrate the Tiny family high speed PWM capabilities to produce a sinewave output. It was also incorporated functions to play Piano Key Tones using sinewave waveform, as a smooth and clean sound as the ones produced by cords.The sinewaves produces are better in low frequencies. source

A two LED flasher is about as simple as it gets.A simple LED flasher is a good project to get started with AVRs. This ATtiny13 based circuit alternately flashes 2 LEDs (or however you want them flashed). Note: Circuit and firmware now available.source

The circuit is rather simple. Main parts are the microcontroller, the light sensor and the RGB-LED. The sensor and R4 are forming a voltage divider. An ADC (Analog Digital Conversion) channel at pin 3 is used to read the values of the sensor. The circuit is designed for 5V power supply. It has no integrated power regulator.source

Strangeness of this clock is in its expression of numbers, which is realized using seven Leds. Leds are located inside a pipe, one above another and if we move Leds enough fast left or right, we have a space where we can write numbers, characters or anything else. source