Ringtone control circuit

Students can set the length of the bell to control everything from getting up in the morning, eating, doing morning exercises, and attending class.
Installing a timer to control the ringing time + such as Is, 2s, 3s, etc. can
solve this problem. Its working principle is shown in Figure 9-3. When the bell is about to ring, press button
SB1. At this time, the time relay KT is energized and the bell is energized at the same time to emit the ringing tone.
Release button SB1. Since KT is closed, the instantaneous normally open contact of KT is self-locking until the time
relay passes the set time (the time relay can be adjusted to Imin or
adjusted as needed), and its delayed normally closed contact The action is disconnected, causing the time relay to lose power and release,
the KT normally open contact is disconnected, and the ringing stops.