情境
A visitor presses the normally open push button; the UM66 melody generator powers up and drives a BC547 transistor to sound the 8Ω speaker.
這張圖裡有什麼
看懂背後的決策。
01
Placed the push button in series with the battery so the UM66 only draws current while pressed.
02
Used a base resistor and base pull-down to keep the BC547 off when the melody IC output is quiet.
03
Connected the speaker between the transistor collector and VCC for proper drive.
Reuse for any battery-powered call bell, UM66-based melody player, or simple 3V audible alert circuit.