I want to build simple and very small circuit.
I have a drone that has 5v output, i want a circuit that when the 5v is lost (drone buttery disconnected) a buzzer start working with it's own battery.
To be clear, i want a small circuit : 3.7-5v buttery, buzzer and a switch that is closed when external 5v goes out also a switch to turn off manually.

Thanks!

 

hi rc,
Welcome to AAC.
Are you able to build small electronic circuits, if a diagram is posted.?
E

 

I want to build simple and very small circuit.
I have a drone that has 5v output, i want a circuit that when the 5v is lost (drone buttery disconnected) a buzzer start working with it's own battery.
To be clear, i want a small circuit : 3.7-5v buttery, buzzer and a switch that is closed when external 5v goes out also a switch to turn off manually.

Thanks!

There are various ways, perhaps the easiest is an emitter follower biased to dump the full input voltage into the buzzer. A second transistor is biased on via a resistor by the main battery voltage. It shorts out the bias to the emitter follower when the main supply is present. Reconnecting the supply disables the buzzer.

You can also use a TO92 style SCR to switch the buzzer and an additional transistor to shunt a standing bias. Many electronic buzzers will not interrupt SCR conduction, so you have to break the circuit or temporarily short the SCR to turn it off. Most electromechanical buzzers interrupt the current, so the SCR will drop out if you shunt its gate again.

 

hi rc,
This is one simple option.
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Thanks for the very fast answer and build, looks good, i will try it out, can you reccomand online simulator?
Do you think a relay can also be used?
Anther goal due the fact this will be mounted on the drone that it will be as small and light as possible .

Thanks again

 

hi,
A relay will make the project heavier.
Most of the low voltage beepers/sounders can be driven as shown using a transistor.

I use a LTSpice simulator, which is not easy to learn, perhaps another member could suggest an on-line sim for you.
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