Bicycle turning direction lamp circuit principle

PESD1CAN electrostatic protection SOT23-3 24V two-way

As shown in the figure, the circuit consists of a multi-vibrator with 555 as the core and some jog buttons, indicating bulbs and so on.
555 and R1, PR2, C2, etc. constitute an astable multivibrator, the oscillator period T=0.693 (R1+RP)C1, the lowest frequency of the illustrated parameter is about 1Hz, the RP can be adjusted to change the frequency, the duty cycle Close to 1:1, VT1 and VT2 are the driving poles. When turning left, press K1, the small light on the left will flash, and the speaker will emit a "beep" reminder sound. When turning right, it is similar to the former. .