I am new to here so bear with me.

I have a project for my employer involving a bell (12V dc) and a momentary switch to activate it. I need a circuit that when the switch is activated for even a split second will ring the bell for 1.5-3 seconds the shut off until the switch is pressed again. The supply power will be 120v ac. Again, the bell will need to start ringing off of the slightest connection from the switch. Any ideas will be appreciated. I'm not very circuit savy so please include the circuit to switch to dc 12v

 

A 555 one-shot circuit will provide the timing that you want, and can be used to control a relay or a MOSFET to switch the 12 VDC to the bell. What is the current required by the bell?

 

It is 0.125 amps.

 

It is 0.125 amps.

That's not very much current, so the power supply should be easy. Your best bet for power would probably be a 12 VDC "wall wart." You would need to find one with a current capability somewhat higher than .125 amps (which is the same as 125 milliamps) ; 200 mA or larger would do.

A regulated unit would be best, but they are not terribly common. You might have to use an unregulated supply and a separate regulator circuit, but that's not difficult.

What are your electronics knowledge and skill levels, i.e., schematic reading, assembly, soldering, etc.?

 

The monostable circuit is in a book at the top of this page. Vol VI-Experiments, Chapter 8

Lucky you, an NE555 can conduct 200 ma so it won't need an external power transistor.

Is your "bell" mechanical or electronic? The mechanical bells are not all that picky about having a nice, clean, regulated power supply at exactly 12.0 volts.

 

#12

It is a mechanical bell, but i need it to be solid sounding and loud. So no large variations in voltage.

Tracecom

I am a very quick learner and have decent experience with schematics as well as soldering and other electronics related topics.

To give you more detail, we want to use a limit switch for the trip switch. A log climber will bump it with a safety rope when he reaches the top. It will trigger a 3 second chime loud enough to be heard by an audience 30 feet below and spread out over a 50 yard radius. After 3 seconds it will self silence and be ready for the next climb.


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#12

Thanks for the monostable multivibrator circuit. I'm going to try it. Ill post results.

 

Since your bell is electromechanical a back emf diode must be used or you will pop the 555.

 

I am new to here so bear with me.

...involving a bell (12V dc) and a momentary switch to activate it. I need a circuit that when the switch is activated for even a split second will ring the bell for 1.5-3 seconds the shut off until the switch is pressed again. The supply power will be 120v ac. Again, the bell will need to start ringing off of the slightest connection from the switch. ...

So this is an electromechanical bell. Does it strike only once when the power is applied like a gong, or is it a repetitive striking as long as power is applied like a fire alarm bell?

Ken

 

You can can increase or decrease the ring time by changing the values of either R2 or C1.

 

#12

It is a mechanical bell, but i need it to be solid sounding and loud. So no large variations in voltage.

To avoid large variations in voltage, use a large enough power supply, as tracecom recommended.

My point is that a mechanical ringer doesn't need an excellent regulator. A common wall wart should be good enough, even if it isn't "regulated".

PS, excellent schematic, CDRIVE.

 

The bell will hit repeatedly until power is cut at the end of the timer.

Can somebody post a modified version of the mono stable circuit quoted above with the protection for the 555 inserted?

 

It's in post #9