We (Fitsense, now Fitlinxx) used RFM 300 and 900 Mhz transmitters and=20 receivers and yes, they are susceptible to noise getting in, so we used=20 a checksum scheme to check the packets. If it was 2 way, the unit=20 acting as master would re-request any corrupted messages. One way=20 beacons were sent once per second, and if some were lost, it was not a=20 big deal. This was speed and distance data sent from a footpod to a=20 wristwatch. They are using Nordic 2.4 gig modules now, and the burst mode makes it=20 much less load on the processor, as the receiver does all the error and=20 address checking, and data can be clocked in / out at any speed. So, we had error detection, and error correction was not needed. Joe W On 10/12/2011 12:03 PM, doug metzler wrote: > I've played around with those sparkfun transmitter/receivers. the > biggest problem is that what you send isn't always what you get, so > you'll need to implement some sort of error correction or multiple > message protocol. > > I eventually went to modules that have error correction built in. > They're more expensive. > > DougM > > On Wed, Oct 12, 2011 at 8:11 AM, Joe Wronski = wrote: >> On 10/11/2011 11:16 PM, V G wrote: >>> Hi all, >>> >>> I want to make a simple, cheap, quick, reliable (no one dare say you ca= n >>> only pick only x) garage door open detector that will light up an LED i= n the >>> house/beep a speaker if the garage door is open. I know all it takes is= a >>> mechanical switch, but I'd rather not use any moving parts. I'm thinkin= g a >>> very bright infrared LED and IR transistor with a piece of foil mounted= on >>> the inside of the garage door. If the door is closed, a series of LED p= ulses >>> will hit the aluminum foil reflector and bounce back to the IR transist= or >>> and signal the device that the door is closed. Will this work? I've nev= er >>> done any IR work, so I don't really know what power LED is required, wh= at >>> the distances are, etc. >>> >>> As for the micro controller unit, I can make it wireless and signal the >>> indoor unit via something like this >>> http://www.sparkfun.com/products/10534but I'd have to impliment >>> encryption on the micro controller itself. It >>> would also interfere with other units in the same band, which is very v= ery >>> undesirable. How hard is it to implement simple encryption? >>> >>> Xbee is cool, but it will add $40 at least to the cost of the project. >>> >>> Any other ideas? >> I'm curious, why is encryption an issue? Who, within 400 ft of your >> garage, and with the receiver to read the signals, would care about the >> state of the door? >> As for interference, low data volume and low update frequency stuff like >> this spends very little time on the air. You could send one or more >> 10 mS burst at some fairly large interval (minutes) and be reasonably up >> to date with the door. That shouldn't be a problem unless it >> interferes with something that is data critical. >> >> Joe W >> >> -- >> http://www.piclist.com PIC/SX FAQ& list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .