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Electrical reset of a buzzer

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dkace

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buzzer reset circuit using relay

Hi all!

I have this problem: I want to have a buzzer sounding every time a switch is closing ( ie a door).
I want a reset button to stop the sounder and yet be ready to sound the next time the door is open again.
I tried several configurations with relays and switches but I haven't got the correct one yet.

Can anybody help? I know is a text book circuit, but I can't FIND THIS BOOK!!!
Thanks,
D.
 

buzzer with reset button

Try get hands on PICAXE-08 microcontroller (8-pin PIC with Basic Interpreter) ..
The code for this job will be something like 5 lines ..
https://www.technologystudent.com/pics/picax1.htm
One input pin may be dedicated to the door switch, another input will be reading the RESET button and one of outputs will drive a buzzer - everything can operate of 3 x AA batteries ..

Regards,
IanP
 

buzzer and light reset switches

Thanks IanP, but I prefere not to use µC but relays. I know that it is much more easier to use one pin to control the buzzer and the reset button, but my application should be with electrical equipment only ( long story).
I am about to use logical gates to solve it and then tranfere the solution to electrical relays. Before that has anyone a good idea?

D.
 

Hi Dkace,

Here's a circuit that will do the trick. If the doorswitch is activated
the relay will pull in and the holding contact will keep it pulled in.
When you press the reset button the relay will fall off after the capacitor
is charged. When the door switch is opened the capacitor will discharge
trough the resistor and the circuit is rearmed. You have to select the
capacitor value so that the relay pulls in only a tenth of a second or so
and the value of the resistor large enough not to keep the relay pulled in
when the doorswitch is permanently activated but small enough to rearm the
circuit rapily, let's say a second or so.
Don't tell any one I designed this ! :D

on1aag.
 

    D

    dkace

    Points: 2
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Ok time for dumm questions:

1. Why the capacitor will charge after reset button is pressed? There is no voltage difference between two plates.

2. Reset button function ( when pressed once does it returns to nominal position or goes to another)? If returns to nominal, then new path to the ground, therefore coil is on again. Please clarify.

D.
 

Hi Dkace,

The capacitor will charge because it is discharged the moment the relay pulled in.

If the door switch is still closed the moment the reset button is pressed, the
capacitor will charge again and hold the relay pulled in for about a few tenth's
of a second. You will have to push the reset button until the buzzer stops, maybe
a second or so. The moment the door(switch) opens the capacitor will discharge
trough the resistor and the circuit will be ready to activate the relay when the
door is closed again. The doorswitch is a normally open and the reset switch is a
normally closed type of switch.

on1aag.
 

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