Would appreciate some help in inserting a buzzer into this system

Greetings, appreciate your looking at this.

I have a problem with my kids leaving windows ajar when we go out. & we sometimes come back to uninivted guest who've come in thru these gaps.

I rigged this up & it works ok enough but i sometimes forget to glance at the lights as we leave, a buzzer would be a nice addition and i figure its got to be in series with the master switch but it just doesn't seem to work out.

What am i doing wrong ?

Thanks again

dougw over 11 years ago

Hi Sathesh,
That is a pretty neat system.
The buzzer needs to be in parallel to the lights. Just connect it across a light. If you want it to activate from any of the switches, you could use a diode from each light to one terminal of the buzzer - the other buzzer terminal could go to the common battery terminal. If you want just one light and one buzzer, the left side of every switch in your drawing may be connected together and feed one light and one buzzer in parallel - then you wouldn't need any diodes.
Doug
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Former Member over 11 years ago in reply to dougw

Thank you very much !
Will try it out next week end,
Actually this project is in my car and works on detecting unwound up car windows when i leave the car in a rush.
I tried asking for help in other forums but it was deemed as a vehicle modification - hence couldn't be answered by them. This system is totally independent of the car's circuits - call it an epiphyte!
Strange thing is that as far as i can tell there isn't a car out there that tells you your windows are unsecure when you leave.
Thanks again
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dougw over 11 years ago

Here is a diagram of one way to do this ...

Doug
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jvdberg@ieee.org over 11 years ago

To sense if any lamp is lit and sound a buzzer, you can use a transistor. For this application you need a transistor that can handle a high base-current. For instance a BD241 which can handle a base current of 1A. The capacitor between base and emitter is to short any AC signal that might be picket up by the wires. A value between 0.1μF and 1μF will be good in most cases.
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Former Member over 11 years ago in reply to jvdberg@ieee.org

Greetings ,
Thank you for your kind assistance.
I will try it out at the next opportunity

N.Sathesh
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