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Need help with 555 timer circuit

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BrownOut

Banned
What do you mean by "it keeps repeating the timing over and over"? This circuit will turn on the buzzer after a predetermined time, and continue to buzz until you turn it off. When you turn it on again, the process will repeat. If it's behaving in any other way, you've made some mistake when you built it.
 

audioguru

Well-Known Member
Most Helpful Member
The circuit is not a timer. It is an oscillator that turns on the green LED then turns on the red LED then turns on the green LED again then turns on the red LED again over and over.

You could add a counter IC to count how many times it oscillates then the output of the counter turns on the reset pin of the 555 to stop it.
 

BrownOut

Banned
It's not an oscillator. Pin 2 charges to VCC and remains at that level until the power is cycled.
 

marcbarker

New Member
I might be wrong, because I only breifly looked, maybe someone can confirm this: The description of operation doesn't seem to match my understanding of the circuit design published.

It looks like pin 7 is connected when it isn't meant to be, if it's what I think it is, the circuit will auto-repeat, contrary to the description. If that's the case, then just cutting pin 7.
 
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BrownOut

Banned
Pin 7 is connected exactly as in the monostable mods diagram of the As pin 2 is held high by the 33k resistor, I don't think pin 7 makes any difference. Connect it or not, IMO, the operation isn't affected.


EDIT: According to my simulation, pin 7 makes no difference at all. It can be connected or not. However, if the power is to be cycled quickly or often, leave it connected. NOTE: for those who read my earlier edit ( now deleated ) I had made an error in simulation and got a erronious result.
 
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marcbarker

New Member
Yes that's right, of course. The 555 won't retrigger until pin 2 is dropped again. It only drops the once when power first applied.

Connected pin is 7 better, since it ensures that the next time period starts with a freshly discharged 200 uF (current-limited to sink current of pin 7). I guess that's why it's called 'discharge':)

**broken link removed**

You power it up, green LED on, time period......
Then beep + red LED. It stays this way, until it's turned off or battery runs flat.

If it's re-triggering, it's most probably something to do with pin 2, maybe the track not cut properly.
 
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audioguru

Well-Known Member
Most Helpful Member
I was wrong.:eek:

That is correct.
The 555 will continue to oscillate if pin2 is shorted to pins 6 and 7.

The circuit should light the green LED while it is timing then light the red LED and power the buzzer after the timeout.
 

fonddeath55

New Member
So to make it only go one i just cut what copper tracks? because its just on a proto board not a pcb? And if that wont work which counter ic would you recomend?
 

marcbarker

New Member
If AG says a shortcircuit between pins 2 and 7 would cause your circuit to continually re-trigger, then I am saying look between pins 2 and 7 of your circuit, and see if there's a slither of copper track you haven't removed fully. Geez! :)
 

BrownOut

Banned
No you don't get it. You need to build and operate the circuit just as in the link you provided.
 

marcbarker

New Member
o i get it then well whats a good counter ic

After detailed peer-reviewed analysis, I can confidently say that the best IC for the circuit you built is a 555 timer.

I believe you may have a 555 already, if not check again in the kit of parts for a 555 in case you overlooked it.

I sincerely do hope that the problem with the circuit is only a short between 7 & 2.
 
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BrownOut

Banned
I think the circuit might be working properly and the OP just hasnt understood how it operates. In his first post, he siad the circuit continues to cycle after the original time out. Why is the circuit still operating after the timer has activated the buzzer? The circuit should be turned off untill it's needed again. If he's truning it off, then back on, it will continue to cycle. That's how it's supposed to work.
 

fonddeath55

New Member
I know thats how its supposed to work but it keeps cycling ill just try to find out whats wrong with it. Im going to make a pcb for it anyway in a little so maybe rebuilding it will fix it
 

marcbarker

New Member
You haven't mentioned whether or not you've checked it for a connection between pins 2 & 7 that shouldn't be there! :)
 
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