Circuit help

[curry87]

I have this circuit wrired to a door so when it opens makes a sound etc however i have some problems with it they are it triggers slightly sometimes on its own even without the door being opened.
any ideas how i can change it to prevent false alarms ?

 

[ericgibbs]

I have this circuit wrired to a door so when it opens makes a sound etc however i have some problems with it they are it triggers slightly sometimes on its own even without the door being opened.
any ideas how i can change it to prevent false alarms ?

hi,
I unzipped your file, but the .sch is being reported as an invalid file, just post the file image directly to your text.

 

[curry87]

Forgot to add the transistors have a gain of 200hfe(dc).

 

[Grossel]

Most probably, the switch isn't properly closed.

Try replacint the switch and see if it got better.

 

[curry87]

I put a thin piece of break wire across the door across the switch to see if it was the switch not shutting properly and it still triggers the speaker slightly every now and again.

 

[ericgibbs]

hi,
I would connect the switch from the Base of the 1st transistor to 0V, not the junction of the two resistors.
Also connect a 10nF cap across the switch contacts.

 

[Grossel]

ericgibbs: You're right. The two transistors is connected wrong. If it's intended to be a darlington pair, the forst transistor (leftmost) must be conected to colector and base to the other one.

I didn't detect that error at first glance.

 

[Ross Craney]

Why have the electronics at all. Just a switch , battery & piezo will do.

 

[Jony130]

Maybe you can try reed switch with magnet instead of wire loop.