Why is there a perceptible delay, ca. 1/4 second or so, between pressing a button on my remote car door opener and the door’s actual locking or unlocking? I thought electrons were faster than that.
Here’s my guess.
The door-unlocker-sensor probably needs, say, a quarter-second of continuous signal before it will unlock your door. That way it will ignore random, stray or accidental signals that might otherwise pop your locks when you’re not around.
Just like your modem has a max rate at which it can send data down a phone line, so also is there a max rate at which your remote can send data to your car. It would be quite slow compared to modem speed because the possibility of interference is much higher. I would also guess that for security the amount of info the remote is asked to provide is quite large.
If it is a fancy ‘intelligent’ system there may be a considerable two-way traffic as the car asks the remote detailed questions to prove its identity.
It takes about 50ms (0.05 seconds, or 1/20 of a second) to transmit one code word on a typical remote car-entry system, and about 0.1 seconds for the decoder chip in the car to think about the code (it has to decrypt it, etc.). There’s a fair amount of math going on to decode the rolling-code encrypted signals from the remote. Also, it might take more than one code sequence if it got garbled.
For more detail than you probably want, including flowcharts and timing diagrams, here’s a datasheet on a typical decoder chip: HCS512 KeeLoq Code Hopping Decoder
Arjuna34