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Why are 24GHz presence sensors slow to respond?

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e100:
Does anyone know why the newer generation of human presence sensors operating in the 24-60GHz range take several seconds to respond to large changes in the environment?

Their slowness of response means that they are only useful when paired with a standard PIR sensor to trigger when someone enters a room.
However, once you are in the room they do a great job at detecting the tiniest of movements that the PIR sensor doesn't see.

MathWizard:
Wow thats fast stuff, so can you would put that in a hallway or doorway as an alarm ? Well I'm suppused to make optical versions or something, but I never heard of such sensors before, and they are cheap, $20CAN.

I guess they talk right to a modem/or Bluetooth. When the power goes out I'll have to string up tin cans tho.

thm_w:
Several seconds? It looks like its instantaneous.
But then you probably average over time to avoid false alerts.

9:30 in here:


PwrElectronics:
Late 90s I was involved with a project to make a low cost ground speed radar.  We used transceiver modules from MACOM at IIRC 24.125GHz that were originally designed for automatic opening doors on stores/markets.

At the time, pre-GPS; there was a market for things like that for agricultural applications.  I think there is still a very small market for that sort of product but have not kept up.

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