Interface für uP-Systeme (seriell, V24, RS232C, Pegelumsetzung)

While on the subject of doorbells (see Random Tune Doorbell, elsewhere in this issue), an alternative gimmick is worth considering. The circuit of this bell may at first sight appear similar, but there are basic differences between the two designs. In the Random Tune doorbell circuit, a `random` succession of tones with `random` lengths is produced as long as the bell-push is held down. As soon as the button is released, the `melody` stops.