> Hi all,
 >   Back in High school we built water rockets from 2 liter bottles
 > and shot them into the air with an air compressor.
 >
 >   I am going to build some more, this time adding a PIC to it to
 > record its highest altitude.  Does anyone have any ideas on how
 > the altitude can be determined?
 >
 >   Also if anyone has done any projects involving rockets and
 > microchips please email me.  I would be very interested to hear
 > what you have done..
 >

One way of detecting point of apogee could be visual detection of the
horizon, or better the sun. Recessed light to voltage sensors e.g.
TSL250 by Texas Instruments could be along the cone. When the rocket
is on its side apogee is detected.
A PIC such as 12c672 (a favourite of mine) could detect the highest
value on a detector and take this as the level to look for moving
through the other sensors.
I intend to give this a go so I will report my results.
I know optical horizon sensors have been used with model aircraft for
years.
Actual height?  acceleration and a detected apogee would be a start.

Lance Allen