Elwood the Electronic Watchdog

Elwood is a dog who has a very simple behavior. He barks whenever the doorbell rings. Also, he will bark if the phone rings provided that his human, Elmer, is snoring.

Let's design a circuit for Elwood. His input sensors (bits) are:

A value of 1 indicates ringing. A value of 0 indicates no ringing.
A value of 1 indicates ringing. A value of 0 indicates no ringing.
A value of 1 indicates snoring. A value of 0 indicates no snoring.

Draw the circuit which demonstrates Elwood's barking behavior:

Solution: