A classic "fun" project. Using a microphone, a tone decoder (the famous LM567), and a flip-flop, this circuit lets you turn a lamp on or off by whistling. This is the grandfather of modern "clap switches." As a teaching tool, it demonstrates frequency filtering and audio amplification beautifully.
| Circuit type | Elektor page | Key components | Measured output | Match simulation? | |--------------|--------------|----------------|----------------|--------------------| | Wien bridge oscillator | p. 47 | LM358, 10k/20k, 10nF | 1.59 kHz sine | Yes (within 5%) | | 555 astable | p. 112 | NE555, 10k, 100k, 10µF | 0.7 Hz square | Yes | | 4 MHz crystal osc | p. 204 | 74HC04, 4 MHz XTAL | 3.999 MHz | Yes (load cap adjusted) | elektor 305 circuits