Principle of long delay circuit with large adjustable range

Probe high current needle 120 needle head diameter is 3.0 threaded needle high current needle total length is

Adjustable capacitor Murata genuine original

TZC3Z030A110R00 MURATA Murata adjustable capacitor original spot

As shown, the circuit consists of two 555 and a small number of RC components. IC1 (555) and RP1, R1, R2, C2 form an astable multivibrator, the oscillation period T=0.693 (RP1+R1+2R2)C1. The oscillation frequency is about 35~60Hz, which can be changed by adjusting RP1. . IC2 and R3, C2 form a controlled delay circuit. When the power is turned on, press K, then C2 is short-circuited and no charge is accumulated. The oscillating square wave output by IC1 charges and discharges C2 through R2. Since the pulse duty ratio is large, the charge will accumulate on C2 every charge and discharge process. The voltage on C2 will rise. When the charge exceeds the threshold level of IC2 by 2/3Vdd, IC2 is reset, pin 3 is low, K is released, and timing ends.