Two-way electronic music doorbell circuit

Orientation electronic music doorbell circuit is shown in the figure. When the double-gear button SB1 is pressed in place A, the power phase line passes through SB1, a single outside line, and
passes through the normally closed contact of the SB3 button in place B to form the same path as the neutral line in place B.
At this time, the electric bell in place B sounds. Because while pressing the A button SBI
. The normally closed point of the double-speed button SB1 is disconnected, so the local (A) bell cannot
be energized to make a sound. Similarly, when button SB3 in place B is pressed, only
the bell in place A will be energized to make a sound, and the bell in place B (local) will not make a sound.
This circuit has only one outside line, which has the advantages of saving wires and simple wiring.
During installation, the phase lines connected to ground A and ground B should be the same phase line. If one end is
U phase and the other end is V phase, when both ends press the bell at the same time,
the U and V phases will be short-circuited .