Hi all.

I'm trying to design an altimeter/variometer (rate of climb/descent) using a
16C84 + 12 bit A/D and a Motorola absolute pressure sensor (MPX100A). I'm
facing some challenges with the vario part and I would appreciate any ideas
and suggestions...

Most commercial varios use two sensors, one updating slower than the other
one, and comparing the outputs, one can get a reasonable acoustic indication
of the rate of climb + altitude indication (LCD) with a resolution of about
30cm. I think that one can use some simple digital differentiation algorithm
to do the work with one sensor, i.e. get measurements every 100ms and compare
the current value with the old one. Has anyone really done something similar?

Another problem is the temperature compensation of the sensor. Motorola
recommends 'simple resistor network', but doesn't mention what network, what
resistors, what values, etc. Maybe one can use the spare A/D channels to read
a temperature sensor (LM35), and do the job in software?

And a third problem is, how does one cheaply calibrate a vario? All elevators
in Cape Town look the same, and have presumably the same rate of climb :-)

Regards,

Richard Ivanov
Cape Town

Richard Ivanov, Cape Town <-- new politically correct sig