Simple NPN Timer Circuit Switch...

[Racer53]

I am trying to design a ,simple as possible, timer circuit...I am using a cheap dollar store timer and I have run wires from the alarm buzzer...When the alarm goes off it produces .10 volts...I need this .10volts to switch on my circuit[running off of a 9v battery] that will trigger a light...My problem is my lack of knowledge on how to make this work...I know I can use an SCR, but I would rather work with a NPN transistor...Again trying to keep this as simple as possible...

Welcome any ideas or thoughts...

Thanks, Racer53

 

[Reloadron]

The biggest problem you face is the .1 volt signal is not enough to much with. Is the .1 volt with the buzzer in circuit (measured across the buzzer) or with the buzzer out of circuit? If in circuit you may want to remove the buzzer and see what you have to work with. Problem being that .1 volt is not going to get a transistor into saturation to act as a switch which is what you want.

Ron

 

[Racer53]

The biggest problem you face is the .1 volt signal is not enough to much with. Is the .1 volt with the buzzer in circuit (measured across the buzzer) or with the buzzer out of circuit? If in circuit you may want to remove the buzzer and see what you have to work with. Problem being that .1 volt is not going to get a transistor into saturation to act as a switch which is what you want.

Ron

Ah yes...I went back and removed the buzzer/alarm and am now getting .40volts...If I remember correctly a NPN transistor need .70v to "fire" correctly...Any ideas on perhaps increasing the voltage before it gets to the NPN transistor...

 

[Racer53]

I'm looking at using another npn transistor as an amplifier but still am welcome to ideas...

 

[Reloadron]

You can It should give you a few ideas as to using a basic transistor like the 2N2222. Something I am not sure about is if the voltage you have is actually a DC level or if the buzzer it was driving was actually a tiny piezo speaker device being driven by a frequency.

Ron