Hi folks, having a bit of a problem with one of my projects. I'm quite new to playing around with electronics so need some help.

The circuit I'm trying to make contains a flashing led to show that the circuit is running but when a switch is opened (circuit broken), the power to the led is cut and goes to a speaker that makes a deafening beep noise that beeps at the same frequency as the led did.


Oh! And it has to run off as small a voltage as possible because it has to attach to my dogs collar! When he's tied up outside he has a habit of breaking the collar off and i want to run a wire through it so if it breaks then the chain will start beeping loudly to alert me! Even if it runs off button cells I don't mind replacing them as long as the led flashes for a few hours and still has enough juice in the battery to sound the alarm!

Any help would be greatly appreciated!

 

The easiest way to do this would be with a SPDT switch (single pole, double throw). You'd connect things so that when the collar was closed (on the dog), the switch was depressed so that the normally closed terminal is open. Then, when the collar separates, the normally closed terminal closes and powers the speaker. Thus, the electronic solution becomes fairly simple; the hard part is devising the mechanical device. It also has to be robust, as animals can be pretty rough on things.

The other method of having a wire that causes something to activate when it's broken is a little more complicated, as you have to have a current running through the wire and a circuit to detect when that current is interrupted. Not difficult, but it's more components and continuously runs the battery down.

 

Does it have to have an LED( can run longer if LED was not draining battery)? Or does the LED have to flash/Blink??

 

This is a good hobby project for learning electronics.

Please don't take this criticaly.

But is there any way to get a different stronger collar, or fix the collar so it can;t be broken so easily, because it sounds more like a mechanical fix, for the safety of your dog not getting loose, rather than an oppurtunity to do an electronic experimentation.

I mean this in all sincerety, not in ridicule.