Re: Re: Driveway sensors

["Clive Chapman" <clivechapman@xxxxxxxxxxxxx>]

Ian Wrote.

>
> > May be beam sensors are the way to go...
>
> I read an article on making your own beam 'break' detector recently
where
> it worked on a reflection basis just like the hand dryers in toilets.
I
> don't remember the range it worked over but it was adjustable. Just
another
> option? It would mean just one unit not two as a conventional beam
break
> and may be easier to isolate from the effects of sunlight.
>
> Ian



Most of these types of sensors use infrared light which is why sunlight can
be a problem.  However if you modulate (Turn the IR light on and off) the
IR
light at a known frequency on the transmit side it is easier to
descriminate
this from any other signals at the receiver.

That why infrared handsets are modulated at specific frequencies.  To
reject
interferrence via sunlight and IR from plasma/CRT screens.  i.e. 38Khz

My guess is that using a reflected system is easier as driving IR between
two gate posts is pretty tricky.  You would need  quite a bit of power,
also
you have to then deal with beam alignment.

Clive