Music logic test pen

The circuit is shown in the figure. It consists of a pair of complementary signal detection control tubes VT1 and VT2 and an 8-sound effect music integrated circuit HY-88. It uses a micro speaker to produce sound and judges the measured logic state according to different music.

Circuit Principle: The HY-88 is an 8-sound effect music integrated circuit packaged in a PCB (printed circuit board) package. It has eight trigger control terminals, S1 through S8. Low-level triggers activate, corresponding to eight animal sounds pre-stored in internal ROM (read-only memory): insects, crickets, frogs, cuckoos, cats, dogs, cows, and horse hooves. Adjusting oscillator resistor R4 changes the pitch of the sounds. The audio signal is amplified by VT3 and drives speaker BL for sound. VD1 and VD2 are step-down diodes, ensuring that the operating voltage between Vdd and Vss falls within the 2.5V to 4.5V range. The detection status of the logic pen is as follows: (1) When the probe T does not touch the circuit or detects "hanging", VT1 and VT2 are both cut off, and the trigger terminals s1 and s2 of IC are pulled up to "1" by R3 and R2 respectively, the IC does not work, and BL is silent; (2) When the probe T detects "0", VT1 is cut off, VT2 is turned on, s2 is "1", s1 is triggered by "0", and BL makes an insect sound; (3) When the probe T detects "1", VT1 is turned on, VT2 is cut off, S1 is "1", S2 is triggered by "0", and BL makes a cricket sound; (4) When the probe T detects the "CP" pulse, VT1 and VT2 are turned on in turn, s1 and S2 are triggered alternately, and BL produces both cricket and insect sounds.