Re: RF Link

From: Mark Jones (abuse_at_127.0.0.1)
Date: 02/05/05 

Date: Sat, 05 Feb 2005 10:14:20 -0500

eric781@gmail.com wrote:
> Well here is the dilemma... I need to know if object A is too far from
> object B, and if so will send a "1" to the chip in A. I was told that
> RFID is the only technology avaible to do this easily, but RFID is way
> too expensive to implement at this point. I was hoping to find another
> low cost RF solution.
>

 Well, there are several things you could try. The easiest would probably be a
simple low-power RF signal generator, which only puts out enough power to be
measureable from your "good" distance. This has the disadvantage that simple
obstructions may give a false "too far" result of your receiver.

 An other idea, much more involved, would be to send an RF pulse from B to A and
back to B, measuring the delay in nanoseconds. You perhaps could do this with a
fast microcontroller chip - enable interrupts, send RF pulse, start timer -->
interrupt happens, stop timer, timer value = delay. Since the speed of RF in air
is known, the time taken to ping-pong an RF pulse back and forth between these
two points can be turned into a physical distance.

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