> No!  No matter where I pointed the thing, the IR detector detected =
it.
> I even put aluminum foil around the IR detector, and still it would=
n't
fail
> It is just a Gr=FCndig TV and remote.
>
> What am I doing or thinking wrong?

You're not doing anything wrong - the problem is that those types of
receivers are designed to be quite, in some cases very, sensitive to
the sort of IR transmission used in remote controls. ie data on a 38k=
Hz
carrier. I often use them and sometimes need directional shields and
it can be troublesome to get it just right sometimes. As you've found
out, they'll easily detect reflected beams. You could try toning down
the transmitter (increase the LED's series resistor)

> I tried to move from IR to sonar, but I cannot understand how the
> electronic portion works for the receiver

Sonar, eg 40kHz, is easier to detect distance with at a basic level, =
as
the speed of a sound beam is substantially slower than that of a ligh=
t
beam (ie the IR). You could use "pings" and measure the time of fligh=
t
for longish distances, or a phase detector to measure reflections fro=
m
nearby objects. That is where you compare the phase of an outgoing
wave to the phase of the incoming wave

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