Tire flat alarm circuit

This is the circuit schematic diagram of a bicycle tire leakage detector. The sound of the air flow in the leaking part of the inner tire of the car is received by the microphone BM , converted into an electrical signal, coupled to the transistor
VT through the capacitor 6 for amplification, and then passed through the coupling capacitors C3 and C4 and the volume is selected by the potentiometer RP. The power amplifier SL31 is fully amplified and the sound is played by the earphone EJ.     The bicycle tire leakage detector uses a low-voltage integrated power amplifier circuit SL31 (or LA4101). Its operating voltage can be selected between 2 and 4. 5V, and the current working power supply is 3V. The transistor VT uses silicon NPN transistor 3DG8, which has low noise and is helpful for identifying gas rejection faults. The value should be above 120 and the penetration current J. . Stop if less than 1. Headphones can use 8n low-impedance earplugs. Electret microphone BM uses non-directional miniature electret condenser microphone CR22-9B . The remaining resistors and capacitors are all small components. The outer shell can be made of transistor small radio plastic shell, with dimensions of about 68mm×s8mm. The working power supply uses two R-type batteries connected in series. Potentiometer RP is a small synthetic membrane potentiometer type WH15-K22 with power switch.