Hello everyone.

I'm new here and I've been looking at the forum to familiarize myself with the topics, which I will continue to do daily.

What brings me here? I've built a variable timer with a 555 that can be set to between 10 seconds and 10 minutes, approximately.

I want a buzzer to sound when the set time is up, which I did, but with a disadvantage. Since the buzzer is activated when the 555 output is low, it also sounds when the circuit is energized but the timing has not yet started. Is this possible without complicating the circuit too much?

I hope I've explained myself well.

Your answers will be welcome.

Thanks to everyone.

 

Welcome to AAC. Please show us the schematic for the circuit so we know what we are dealing with.

 

Welcome to AAC. Please show us the schematic for the circuit so we know what we are dealing with.

Here I show my circuit. Thanks.

 

Is this possible without complicating the circuit too much?

Will need to add another 555 circuit to drive the buzzer.

 

Hi. Thanks for the reply.
I had thought about that, but I didn't know how to trigger it from the other circuit.
I have added your proposed circuit to the simulation, but unfortunately it doesn't work. The 555 output from the second circuit never goes positive. Unless I'm doing something wrong.

Regards

 

Must be doing something wrong as it works on my breadboard.

 

I check it and I don't see the fault. Four eyes see more than two.

 

Change C2 to 100nf and see if that works in the sim.

 

It doesn't work either. I was once told that the simulator can fail, but I don't believe it's something that simple.

 

Below is the LTspice sim of my take on a two 555 circuit:
The relay coil current is the blue trace.
It resets the second 555 to stop the output.

 

It doesn't work either. I was once told that the simulator can fail, but I don't believe it's something that simple.

Forget the sim, try breadboarding the circuit .

 

Tienes razón. Lo hice de todos modos porque me faltaban algunos artículos. Lo intentaré de nuevo mañana después de realizar la compra.
¡Muchas gracias!

 

With some tinkering and a lot of magic I managed to make the buzzer sound in the simulator, but with the same problem that I mentioned in my first post.
The buzzer sounds when the output of the first 555 is low. And this is the original state of the circuit before pressing the start button of the timer, so the buzzer sounds without having activated the timer and stops, logically, when it starts.
I think, conceptually, that with these elements it is impossible to avoid this behavior, unless the start button activates a relay or another device that energizes the circuit simultaneously with the start of the timer.
I will try to deal with this.
Any opinion or suggestions are welcome.
Greetings.

 

It will work on the breadboard.
Try changing C3 to a 1uf cap in the sim.

 

With some tinkering and a lot of magic I managed to make the buzzer sound in the simulator,

How did you manage that?
Meaning what changes to the circuit or simulator were made.

 

The tweak to the simulator was that I added a series resistor between OUT and the buzzer. It worked once. Never again. (?)
Afterwards, almost playing, I hit the STOP button while the timer was running. Then it beeped again.
I think the simulator is not working properly.
The issue that motivated me to post is the one I mentioned before. Whenever OUT is low, it will beep, whether the timer has been activated or not. I think your opinion is different and more well-founded. I am just an amateur with little knowledge.

 

I agree the simulator is not working correctly.
It will work on the breadboard if the components are connected properly.

 

MisterBill2 said:
"If it is a switch that triggers the timer, use a double pole switch with the other half opening the buzzer circuit when the timer is not triggered."

Variation of the above suggestion.
Sw1 is a DPDT toggle or locking type push button switch shown in the Reset position.

 

If the buzzer is to stay on until power is reset, perhaps a thyristor is the answer:

 

The buzzer only comes on after the time delay ends and then stays on until reset.