This 9561 should be a music (or analog sound) integrated circuit, its operating voltage is 2.4~3.6V,

F1 F2 sound effect

No connection Answer the police car sound

Connect the positive pole but not the fire alarm sound

Connect the negative pole but not the ambulance sound

Do not connect the positive pole to the machine gun sound

Note : Some 9561s are labeled SEL1 and SEL2

From the circuit structure, R4 should be a voltage dividing resistor, and its size should be able to ensure that the pin voltage is between 2.4~3.6V before and after the IC is triggered. , but it is recommended that a Zener diode of about 3V be connected in parallel between this pin and ground. And R1 is obviously used to adjust the static operating point of VT2.

Any components with * in the circuit must be determined during debugging after the circuit board is assembled.