is there such a switching ic?

[Nishon]

Hi guys
Is there an ic that can take in 12v dc or a momentary contact in its input but keeps the output off but when the input doesnt receive any signal the output must come on? I was reading on the 4013 and the 4069 ic but dont know how to use it.im not very good in electronics but if i have the diagram i will be able to build the circuit.please help

 

[betwixt]

It isn't clear what you need. Are you asking for a device that needs periodically resetting to prevent it changing state. In other words something that detects if a certain period has elapsed without any input.
If that's what you need, the kind of device you are looking for is called a "monostable", a type of resettable timer.

Brian.

 

[Nishon]

Hey betwixt
I think its best if tell you what im doing.im using motion detectors from a distant to activate a buzzer of any movement.the problem is the motion detectors only have a NC relay output.if there is no movement in front of the sensors,the NC contacts pass a voltage to the buzzer constantly and if there is movement in front of the sensors the NC contacts open cutting of supply to the buzzer which works opposite to what i want.i have installed a slave relay to allow the buzzer to sound when something breaks the beam which is what i want.the problem is under normal operation when there is no movement in front of the beam,the slave relay remains energised draining the battery too quickly because its portable without any charger present.That is why i want to usee an IC instead of a slave relay.i hope this explains in detail to you my application.

 

[betwixt]

OK, thanks for explaining. what you are trying to do is reverse the action of the relay without drawing any more current than is necessary.

I'm assuming your relay doesn't have an NO contact as well, if it has, swap the buzzer to that instead of the NC contact. With the present system you will still have to energize the relay to keep the NC contacts open and that will also drain your battery. What voltages are you using for the buzzer and the relay coil? This may be a very simple fix using a transistor instead of the relay and if it's suitable it will draw almost no current at all.

Brian.

 

[Nishon]

The motIon sensors do not come with a NO contact on the relay which would have made life easy for me.everything including buzzer works of 12v dc.if you have a fix for this please paste a drawing.thanks

 

[betwixt]

Drawing attached - sorry for the poor quality!

The transistor must be capable of carrying the buzzer current. If it's a small one, almost any NPN transistor will do, I suggest a 2N2222. If it's a big buzzer (one that starts earthquakes) you will need a power transistor, I would suggest a TIP31A or equivalent.

This circuit draws very little power when the relay contacts are closed, only about 2.5mA which is significantly less than a relay coil would consume. If you are using a power transistor and big buzzer you may have to drop the value of the 4700 Ohm resistor which in turn will increase the current it passes. Without knowing the buzzer specification I can't help further with values.

Brian.

 

[Nishon]

Thanksa a lot Brian,really appreciate your help.

 

[Nishon]

Brian i built the circuit using BD439 and it works exactly as i want,thanks again buddy

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Brian i built the circuit using BD439 and it works exactly as i want,thanks again buddy