I'm trying to build my own sensor network, and I'm hoping to eventually have about half to a dozen sensor all over the house along with a weather station or two outside... Hence me thinking of using xbees for the wireless part of the network. If anyone has a better/cheaper RF that they can recommend, I'm willing to consider it.
Anyway the door bell & closing/opening of the door is kind of a special case, because it can happen at any time so I was trying to design a way for me to wake up the xbee when the event happen, otherwise just wake up every minute to five minute and just report that nothing has changed/happened.
So basically what I was thinking of doing was doing the following:
- Op-isolator (ac->dc) for attaching to the 16v doorbell chime.
- Hall Effects sensor + magnet for attaching to the door to detect opening/closing.
- Some form of logic that would trigger the xbee to wake up when the door bell is pressed, or there is a state change on the door (IE open to closed, or closed to open).
- Some sort of latch? to hold what the state is till the xbee is woken up enough to read and transmit the state.
Basically the goals of this is to get the xbee and the rest of the sensor to be as low powered and stay in a sleeping state as much as possible hence triggering the xbee to wake up. My current issue is how to design the circuit...
Also from reading it seems that you have to hold the line HIGH to keep the xbee in sleeping state, so I was wondering how low I can get that current consumption to be, and also it will still need a low amount of current in the op-isolator and the halls sensor to detect a state change there.