NEED HElP! Circuit explanation

[electronic novice]

hi!
plss. help me with the flow of the diagram

 

[Mr RB]

You took very little effort ot post this request for help, just 14 words and someone else's diagram.

I see from your name you are a novice? How old are you and did you plan to build the circuit or just want to talk about it?

 

[electronic novice]

no its not my circuit someone asked help from me but i cannot explained it, so i posted it. The one who asked from me is my classmate and he wants to build this circuit.

 

[electronic novice]

I really wanted to make the flashing led.

 

[simonbramble]

To make a flashing LED circuit, try googling 555 timer circuits. The 555 timer is a general purpose chip that will make sounds and flash LEDs. Now for the circuit: Firstly the buzzer is a dc buzzer, so it requires a constant voltage across it to sound. if the N/C connection is short circuit, then the base of Q1 is at 0V, so its collector is at 0V therefore the base of Q3 is at 0V which means Q3 is switched off, so no current flows through the buzzer. When N/O is open the base of Q2 (which is a pnp) has no pull down, so Q2 is off, so Q3 has no drive to it, so the buzzer is off. removing N/C pulls the base of Q1 (and its emitter) high thus switching on the base of Q3. Likewise, shorting N/O to ground switches on Q2, driving volts to the base of Q3, thus switching it on

Hope this helps

Simon

 

[electronic novice]

many thnaks

 

[Mr RB]

The circuit you showed in post #1 is not a flasher, it is a "latching" alarm. So once the NC contact has been opened (ie door opened) the buzzer will come on and stay on.

Alternatively you can trigger the alarm with the NO switch.

 

[electronic novice]

no i mean the other post.