I'm relatively new to electronics, I've been studying them in my free time for about a year, and I just recently attempted one of my first builds. The schematic, stripboard layout, and parts list are available here:
Ron, he is not trying to build a free-running oscillator, he wants only one cycle. The RC network on the TRIG pin is there to trigger the 555 ONCE as power is applied.
I figured out something, haha, I realized that the 0.1ufd was misplaced, so now the green LED turns on, but when the green LED turns off, the red LED nor the buzzer turn on. I checked every connection and placement and everything is where it's supposed to be
do you think that it's because I have a 12V buzzer? The schematic said that it would be okay, but the fact that there's only 9V in the circuit, would that maybe be the problem?
I replaced the buzzer with the 470ohm resistor and the same thing happened, I don't know if this information helps, but when the two red LED leads are connected the buzzer goes off.
Then you have a shorted RED Led. If that is a true buzzer (coil, vibrating points), then the inductive kick that happens as the points open will blow up a Led. I think the circuit designer was thinking of a Solid-state Sonalert, not an electromechanical buzzer.