deer breneer
555 IC is a timer with 2 work mode:
1:continued that we define 2 time period with 2 R & 1 C:
Th=0.693*(Ra+Rb)*C
Tl=0.693*Rb*C
T=Th+Tl => f=1.44/( (Ra+2Rb)*C)
2:monostable that we define a time period with 1 R & 1 C:
Th=1.1*Ra*C
in this mode ,if pin 4 (reset`)be high & pin 2 (trigger`)be low then out put
change to high for Th second .
note that we have trigger` not trigger. this IC drive with a high to low pulse
I assume u drive LED & buzzer with low to high pulse . therefore i use a RTL not
circuit before drive 555 .
now I think u drive IC with low to high pulse:
_____ _____
______| |____________________| |________________
before press button buzzer is turn on & when U press button make trigger` high ,therefore after Th second buzzer turn off! we must inverse pulse:
_______ _____________________ _________________
|____| |____|
in this case ,when pulse change to low (when u press button) out put change to
high (turn on buzzer) for Th second.
what do u do before this circuit?
u wrote :
When a button is pushed, the buzzer and light will conduct.
the light and buzzer will only turn off if I will push the RESET button.
so u must use a memory such as flip-flop to turn on & off LED with set & reset button .& run 555 with set` pulse . if u can , use not gate after set button
instead my RTL not .
if u have question ask me.