How to set up a desired threshold voltage?
What I need-A circuit which allows voltage which is greater than or equal to 3 volts "ONLY" to pass through and power a buzzer i.e,shouldn't allow theuzzer to be powered with a voltage lower than 3 volts.
The details-I just finished a project which makes a buzzer sound at its final phase.But,yet another obstacle-A darlington pair first completes a circuit with a relay in it when the base of it receives positive current via a resistor.The relay is activated which in turn powers the buzzer with - ve 12 volts and this makes the buzzer sound as +ve 12 volts is already connected to the buzzer.But somehow the buzzer is making a feeble,rather irritating sound even before the relay is activated..and it is somehow getting powered with a stray 3 volt power due to a leakage,somewhere.I tried to trace the flaw but couldn't find it.What I have in mind is a circuit which will allow voltage greater than 3 volts only to pass through and power the buzzer,somewhat like the function of a zener diode.I kindly request your guidance in designing a circuit which has a threshold voltage of 3 volts and higher.(I'm thinking BC 547s,555 timers etc.).