Here’s a fun project in the Christmas spirit. It’s a “Jingle bells” playing card, with the specific notes being signaled via LEDs as they are being played.
We have 9 control lines for the LEDs and 1 line for the speaker signal. We want the device to start playing if a push button is pressed and when done playing the device shall be switch off automatically. For this, we use a pushbutton in parallel to a relay switch which is controller by the ATmega. If someone presses the push button then the ATmega starts running and holds the relay closed.
Via Hacked Gadgets.