I need some suggestions on a couple of sensors;

1) I need to measure water level (and thus contents) in a concrete tank.
The tank is about 2m deep, so a float is probably not practical. My
thoughts are either an ultrasonic setup to detect the water surface,
or a pressure sensor. The ultrasonic setup will be complicated, the pressure
sensor would either have to be at the bottom of the tank, or above it with
a hose to the bottom. The hose idea would rely critically on having no air leaks
in the hose, difficult to guarantee for a long time. Submerging the pressure
sensor would leave it liable to getting blocked by stuff on the bottom of the
 tank.

2) I need a "light beam" sensor to detect vehicles or people moving down
a driveway - much like a door minder used in shops, but to operate outdoors
spanning a distance of about 20m. It should preferably use infra-red so as not
to be visible (this is not critical, but if it uses visible light it should not
be too bright). The electronics side of this is reasonably straightforward - I'd
modulate the beam at some frequency, recover the modulation and differentiate it
to detect sudden interruptions. This should make it immune to external lighting,
fog etc. The hard part is what kind of light source, detector and lenses to use,
especially for infrared.

All suggestions from this esteemed collection of minds will be gratefully
 received.

Clyde

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Clyde Smith-Stubbs               |            HI-TECH Software
Email: clyde@htsoft.com          |          Phone            Fax
WWW:   http://www.htsoft.com/    | USA: (408) 490 2885  (408) 490 2885
PGP:   finger clyde@htsoft.com   | AUS: +61 7 3354 2411 +61 7 3354 2422
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