Garage Door Opener Gone Wild



Question:
I recalled today that I just installed a new 'intermatic' digital timer switch to control some outdoor lights on the same circuit. However, this new digital switch has a fairly classic 'relay' mechanism (you can 'hear' it close, and it's capable of switching dimmer circuits, motors, etc) which would suggest it's not generating any RF interference on the line. I would find it hard to believe anyway that 'random' RF would be accepted by the door opener, given the security encoding. This switch is stand-alone, it's not part of some system that uses the power-line to carry signals. My opener does not have any electronic eyes; it has a fairly simple mechanical mechanism to cause the door to open if it encounters resistance. I checked that out today and it works. Lights flash when that system kicks in. After cleaning all the contacts, I put it back in operation, and closed the door. Just as I was about to drive off, it opened fully. I closed it, it opened fully again within a minute or so; no flashing lights, just a straight open. I guess the next thing to do is look at the pushbutton switch on the wall, and to remove the new timer switch on the same circuit. And wait...

Answer:
The new timer is still your prime suspect - relay contacts are a notorious source of RFI. Usually the RFI is just a burst when the contacts open or close, but it can be more-or-less continuous if the relay contacts are contaminated. While the RFI might not get past the door opener's receiver circuit, it can still get into the logic controlling the motor via the power line. If you find that the problem goes away when you disconnect the timer, then you will have to place an RFI filter in-line with the power cord of the door opener. RFI filters on the power supply is an area that a some consumer electronics designers like to skimp on. Other possible things to look out for: o A new ham radio antenna has appeared on your neighbors house. o A neighbor that has recently taken up arc welding. o You notice that when your door goes nuts the electronics hobbiest that lives across the street is laughing hysterically.





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