Hi all.
I have made this circuit and it is working fine without the transistor and relay .
I want to connect a external Piezoelectric Buzzer and flashing LED directly to the output of the 555 chip (pin 3). Im using 12v input and do get 12v out from the pin3.
What I want to know is this: Will the 555 chip output (pin3) be able to handle the current draw from a external Piezoelectric Buzzer ?

thanks so much.

 

Will the 555 chip output (pin3) be able to handle the current draw from a external Piezoelectric Buzzer ?

And how can that question be answered if we don't know what the current draw is?

 

here is what I'm thinking of using.

 

If the Buz only draw 10mA then R3 is drawing too much current, you can use R3 more higher as 6.8K~10K.

 

Hi all.
I have made this circuit and it is working fine without the transistor and relay .
I want to connect a external Piezoelectric Buzzer and flashing LED directly to the output of the 555 chip (pin 3). Im using 12v input and do get 12v out from the pin3.
What I want to know is this: Will the 555 chip output (pin3) be able to handle the current draw from a external Piezoelectric Buzzer ?

thanks so much.

View attachment 157323

Yes, it can handle the current.
LM555 max. output current is 200mA

 

..... and if your LED is a type with built-in flashing circuitry then it will probably (check its datasheet) draw about the same current as the buzzer, so could also be driven from pin 3.

 

So I have a problem now , when I apply 12 volts the 555 heats up to 55 deg C. I don't think this is normal and I'm worried about the life of the chip , seeing as its going into a alarm system I cannot afford for it to fail. It stays hot even if the switch is not activated. Also there is about 3 v leakage out of the pin3. How can I fix this ?

 

So I have a problem now , when I apply 12 volts the 555 heats up to 55 deg C. I don't think this is normal and I'm worried about the life of the chip , seeing as its going into a alarm system I cannot afford for it to fail. It stays hot even if the switch is not activated. Also there is about 3 v leakage out of the pin3. How can I fix this ?

Also note , there is nothing attached to pin 3 when its getting hot.

 

The only thing I can see from the schematic that might be the colpritt is the pot R2. If the pot is at zero ohms then the collector of the discharge transistor is at the supply voltage or it could just be a defective 555. Where did you get the chips from?
SG

 

The only thing I can see from the schematic that might be the colpritt is the pot R2. If the pot is at zero ohms then the collector of the discharge transistor is at the supply voltage or it could be a defective 555. Where did you get the chips from?
SG

 

OK. Not sure what the purpose of the photo is. Did the problem get fixed?
SG

 

Yeah , replaced the 555 , running cool now , thanks so much. Seems these chips are a bit sensitive , lol

 

Hello,

I would mount an 1K resistor in series with the 1M Preset (R2) to protect the 555.

Bertus

 

Another thing , I would be most grateful if someone could help me with the timing , I need the circuit to stay on for 5 minutes , I'm not using a pot , and R2
is currently 100 k. Ohm's , on for 30 seconds.

 

A 1 meg resistor should give 5 minutes or so. It will also require a low leakage timing capacitor when designing longer time delays.
SG

 

Hello,

You could use the calculator : https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/
Using 220 μF and 1.2 MΩ would give you about 290 Sec according to this calculator.

Bertus

 

Hello,

You could use the calculator : https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/
Using 220 μF and 1.2 MΩ would give you about 290 Sec according to this calculator.

Bertus

Hey guys , thanks a million , you have all been so helpfull , as for the cap , I have hundreds of PC boards laying here , what make / brand should I look for ?

 

Something else to think about. I've had better results driving those magnetic buzzers with a transistor just like Q1 does in the relay circuit then directly from the 555. R3 could easily be increased to 10K or more.
SG

 

I would just try using the cap you have now. As long as it consistently shuts off at the time required it should be OK.
SG

 

I would just try using the cap you have now. As long as it consistently shuts off at the time required it should be OK.
SG

Perfect , found a 1M ohm resistor , timer runs for 5 minutes 10 seconds. Again thanks so much for all the help. Now I can't wait to get this alarm system installed , maybe then I can get a good nights rest