My local Open Source Hardware meetup group meets on the second floor of a small brick office building downtown, probably vintage 1920's. For security reasons, the front door of the building must remain locked after hours, so as members arrive, someone has to walk to the opposite end of the building, then down one long flight of stairs, to open the door for them.
But that person doesn't have to do anything but walk into the lobby to release the door lock - apparently it's a proximity or motion sensor, which also works to let people out. So, we were thinking if we could communicate remotely with a device left in the lobby, and perhaps make it turn on a fan or something similar, we could let people in that way.
Ok, I just told you all I know about RF. But the problem is this is an old brick and steel building, and the lobby is pretty effectively shielded just from the construction involved, except that it has exterior windows. So the RF from the second floor would have to go through a window to the outside, then come back into the lobby from the outside. Not exactly a straight line.
I was thinking of using 433 MHz transmitter and receiver modules and something like an arduino. The logic would be really simple. The receiver in the lobby would just wait for some appropriate code at 433 MHz, then turn something on that triggers the motion detector for a few seconds, then go back into waiting mode. One-way communication.
My thinking is that the lower the frequency, the better chance the RF has of turning corners, and 433 MHz might be a good choice for cost and antenna length. Does that sound reasonable, or is there a better choice? From what I can tell, the 433 modules seem to be a pretty popular choice among arduino guys for radio control projects.
Anyway, comments and suggestions would be appreciated.
By the way, the irony is not lost on me that this would be an OSH project for the OSH meetup group attempting the solve the problem - how do I get to the freaking OSH meeting. But that's ok - this project is appropriate for my level of expertise.