Help adding delay to reduce false trigger

[maxedmini]

hi there this is my first attempt at creating a circuit so keep it simple for me please

A quick description
the circuit is used to warn of low coolant on a car
the green led is lit when the ignition is turned on and the red led and buzzer sound when the float closes the switch this all works ok BUT i need to add a delay to reduce a false trigger as i have found the water movement sometime closes the switch for a second and i get a quick buzz and a flash of the led

so what i require is a way to add a delay so if the switch is closed only for a second or so the buzzer and led do not trigger???

the components used are
red LED = 12v 8.5mA
Green LED = 12v 8.5mA
Buzzer = 3 to 24Vdc 5mA

thanks

 

[(*steve*)]

Everything is OK except what you have done with the LEDs. (Adding a delay is non-trivial)

Perhaps those LEDs have an integral series resistor. Otherwise they would have given one bright flash before expiring.

Using a time delay relay may be an option. It has a delay down to 1 second. It may be a little pricey though.

I've tried finding a simple circuit that I would be happy placing in a car, but I've not been successful. I don't want to suggest something that is too hard to build, nor something that will not cope with voltage fluctuations that are common on car electrical systems.

 

[maxedmini]

yes the leds are 12v ones

I have built the current circuit and all works fine except for the false alarms

can a 555 chip be used some way to prevent this??

 

[neon]

USE AN LM555 as one shot for one sec use it as a one shot using pin 2 as triggering or tbreak the line from switch red cathode install a big cap in series to the buzzer and that will spike the buzzer to ground when the switches closes only.