Create door opening wireless notifier? Reed switches?
I have a Vellerman K8055 USB experimental board that I have hooked up to one of my machines. Yesterday, I took our wireless doorbell apart and with a multimeter found the signal that sparks the 'ding-dong' sound when the remote bell is pressed. I wired that into the K8055 and then to cut a long story short, when the bell is pressed, it pops up on my TV and tells me that someone has pressed the bell (using MythTVOSD multicast if anyone is interested).
A link to the card: http://www.velleman.eu/products/view/?country=be&lang=en&id=351346
What I'd like to do is to extend this mechanism to my doors. When a door is opened in the house, then I need a signal to be sent to a receiver device also wired into the K8055 so that I can capture that event in my program.
I have thought about using magnetic reed switches on each door with hacked wireless doorbells (around 3-5 GBP on ebay from China).
One problem I have is that I can only find 'normally open' reed switches, meaning that when the door is closed so will the reed switch contacts - this in turn means that I will be constantly notified (should I be able to make this work) that the door is closed. If I could find 'normally closed' reed switches, I could have one of each on each door,
What is the cheapest/most elegant solution to this problem?
Is using hacked wireless doorbells the way to go, or is there a better way.
I'm a relative novice with electronics - I'm a dot net developer by day with experience of data capture cards, and have toyed with the Arduino, Lm386s, 555s, 4017s etc... some with instructions from this site, so whilst not a complete beginner, I am what I would call, "an enthusiastic amateur'.