LED/Buzzer combination help.

[Rickkh]

I get this circuit to work 'sometimes'
Can you see the problem??
what currents will be drawn?

 

[audioguru]

C4 is backwards.
You don't say if the 555s are ordinary "high" current ones or Cmos ones that draw nearly no supply durrent.
You don't say if the U3 buzzer is a high current mechanical one or a low power piezo one.

The U3 buzzer messes up the input signal to the second 555. Connect U3 to pin 3 of the first 555 instead.

 

[Rickkh]

sorry about that, this is the right one I think
I am using 2 NE555's

 

[audioguru]

I am glad you re-connected the buzzer to the proper position.

Didn't you look?
The datasheet for the NE555 shows its supply current is 5.5mA with a 9V supply. So two have a supply current of um, duh, 11mA. That is the "typical". The current might be more or less.

The operating current of the buzzer and the LED must be added.

 

[Rickkh]

I more meant how would I work it out at various places around the circuit

 

[Gordz]

I have always made sure pin 4 on a 555 is never left floating, if your are using a 'buzzer' as in self interupting vibrator you are going to have big problems.

 

[Hero999]

Unless you add a diode in reverse parallel with it to absorb the back-EMF.

Most modern buzzer are either piezo or use a transistor oscillator to control the magnet so it shouldn't be a problem.

 

[angeljeffph]

i suggest please use this buzzer circuit instead of that: http://www.techlib.com/electronics/games.html

that is the website. i hope i could help you.

 

[Gordz]

As a matter of interest, what are the dimensions of your probes ? And how much of the probe set will be submersed ?