I had a simple idea of replacing the door bell button on a wireless door bell setup with a reed switch. The idea being that I could then use the reed switch to detect when a door or window had been opened. You could say it's no longer a door bell but more of a door or window alarm.

Now this all works perfectly except for one major flaw. Once the reed switch has triggered the door bell circuit it only runs for one cycle. What I actually want is for the door bell to continue to chime for as long as the door or window remains open.

I have very limited electronics knowledge except for the very basics so I'm hoping someone with more experience might be able to steer me in the right direction. I've posted an image of the door bell circuit board (along with what the actual set up looks like) in the hope that someone might know how I can get around the one cycle limit that it currently sets.

I have spent time probing the circuit board with a wire trying to see if I could get around the normal switching cycle. Unfortunately the best I could do was to trigger the switching circuit for the standard one cycle. Maybe I could remove one of the existing resistors and replace with some other value. That's just one of my wild guesses. I thought I'd come here first before I toasted the current circuit board with too much experimenting.

Anyway, I hope the above makes sense and I look forward to doing a bit more tinkering once I have some feedback.

 

I think you will find the one cycle is programmed in.
A mod that could be done is to have your reed trigger an astable multivibrator that turns the door bell transmitter on and off every couple of seconds. That will give you repeatable rings.
Maybe a cmos 555 timer circuit.

 

Can you post a picture of the chimes? The answer may lay in modifying both the transmitter and the receiver. Or at the very least, the transmitter.

 

Door bell pushbuttons are NO (normally open). Press the button and the button contacts close the circuit from the battery to the transmitter. The transmitter is triggered once until the button is released and pressed again.

Fortunately, alarm reed switches operate in the correct fashion for your application. Reed switches are NO when the permanent magnet is brought up to the switch. When the door or window opens, the reed switch contacts are closed.

My guess is that all you need is a CMOS 555-timer circuit in astable mode (about 0.5Hz) wired to power the transmitter.
The reed relay is used to power the LMC555 circuit from the 3V button cell.

 

Fortunately, alarm reed switches operate in the correct fashion for your application. Reed switches are NO when the permanent magnet is brought up to the switch. When the door or window opens, the reed switch contacts are closed.

It takes a magnetic field to actuate a reed switch. IF the switch is SPST then it takes a magnetic field to close the switch. IF the switch is SPDT then you can have either an open or a closed in the presence of a magnet, depending on how you wire it.

 

Another solution is you can buy the 433MHz transmitter and receiver for less than US$2 on eBay and wire up the circuit yourself with guidance from helpful members here on AAC.

 

Firstly I'd like to give a big thank you to everyone for the very valuable feedback and suggestions on how to tackle this project. I must say the idea of using either a cmos 555 timer or a 433MHz transmitter has actually given me some other ideas I had not even considered. I've often seen those modules on ebay but never realized the potential they held. That's why I'm so thankful for the suggestions that have been given. It looks like this project might have given birth to a few more.

Once again, thanks for the great response and I look forward to spending even more time within these forums.