> variometer

If all you want to know is, when you go up, you don't need a variometer,
you need an accelerometer and an integrator, with an auto-zero function
for low inputs.

A piezo accelerometer by Tokin or others, about four op-amps and a PIC
with A/D will do this for you imho. A nice project ;)

0.02 Agorot

Peter

PS: One word of caution: These accelerometers are sensitive and need to be
packed in foam or suspended in an anti-trip setup. After every severs
bang, the zero starts drifting and it's calibration time...