Need help, with 2 circuits

[iflymyhelishigh]

Well, I am an electronics noob, so I am studying up on the 555. I am still very vague on it, and am trying to learn. Bad.

With that circuit, would it be possible to change out the capacitor to a larger uF to have a longer beep time?

I see these circuits in things like my simple timer, but I can't replicate it or trace it. haha

 

[flat5]

Maybe this will work.

Edit: With an inductor there would be a back emf but not with a capacitor. buz2 will never sound.

 

[iflymyhelishigh]

Well, from my electronics experience, wouldn't that buzzer be on 24/7?

Buzzer 1.

 

[iflymyhelishigh]

Hmm, I was thinking, and I could try to apply a simplified concept of a UPS to my beep when power turns off, because it automatically switches circuits.

I really want to try to learn how to use this 555, so I'm off to do research. Help would be appreciated

 

[iflymyhelishigh]

Wow I feel like a post hog, but I came up with a new idea.

What if I were to use a 555 timer as a one shot timer for the turnon, then have a power fail circuit reset the timer when the power goes out? Or can I just reset the timer by turning it off?

 

[ericgibbs]

Wow I feel like a post hog, but I came up with a new idea.

What if I were to use a 555 timer as a one shot timer for the turnon, then have a power fail circuit reset the timer when the power goes out? Or can I just reset the timer by turning it off?

The simple transistor circuit 'flat5' posted will do what you want.

 

[flat5]

"The simple transistor circuit 'flat5' posted will do what you want."

Yeah! I did something right! (If the cap's leakage is greater than a megohm, if not remove the base to ground resistor)

"Well, from my electronics experience, wouldn't that buzzer be on 24/7?"

When power is applied the + side of C1 is always more positive than...the other side of C1.
I don't see why the buz1 would be on all the time.
Do you see a path around C1? (buz2_D1) I don't.

I'm not sure buz2 will ever be on. I just hoped so

 

[iflymyhelishigh]

I'm off to the store to get some components

 

[iflymyhelishigh]

Woo!

It worked. I built up the circuit with some components of mine that I had lying around, and it actually worked. Both buzzers sound, but some modification is needed.

I needed to connect the - end of buz2 to the area of the diode before it actually "diodes" to cause the effect to happen again. That causes buz2 to beep. Considering I was running the tests with 3 volts, it may change later on. I need to head to the store to get the components that I need, a switch with 2 rails. haha

 

[iflymyhelishigh]

There is one problem I see though, and that is the possibility of the capacitor blowing up after voltage has been applied to it too long.

I would think that if it didn't drain out fast enough that it would eventually be overloaded, thus blowing up.

 

[flat5]

You need to read more about capacitors.

 

[iflymyhelishigh]

Hehe I sort of figured. From what I've read, its if you overvolt a capacitor is when it explodes. So lets say a 3.7 capacator being charged with 50 VDC is going to explode... right?

 

[flat5]

The charge a capacitor can hold is not the same as the maximum voltage you are aloud to apply to it.
For instance, you could buy a 100uf 16vdc cap or a 100uf 50vdc cap.

I misread your original post. I thought you also wanted a signal if the supply turned off. Since you only want a notice when the supply turns on you only need one buzzer and not the diode or Buz2.

 

[Giggabite]

I love this Forum ....!

 

[iflymyhelishigh]

Hmm. So I also found out that with your original circuit Flat5, I had to put a resistor between the capacitor to cause the buzzer to sound again after being turned off. I am not sure what kind of resistor to use, because I used a variable Pot to do that.