I'd like to build a Variometer for an RC Sailplane.
Did any body around do that before ?
I'd like to constantly detect variation in altitude of ~ 5cm/s (~50Pa/s). for a range of -300m +700m from the takeoff point. From time to time, I'll need to have an absolute altitude above (below) the starting point.
The common sensors I have looked at won't do that.
I guess I'll need 18bits resolution, which I want to feed into an AVRmega.
Any Idea around ?
Martial
Traditional rate of climb instruments use a calibrated leak, usually some sort of porous ceramic (?) over a relatively large surface area to minimise problems with dirt ingress etc. I would think far too complicated and expensive for this type of application.
A high res adc is no good without a high res sensor, which is very expensive. The trick is to make it all work with a cheap sensor like those used in engine fuel management systems (Sensym/Motorola).
May be usefull to have a look at some of the electronic variometers for recreational gliding to get some idea of how it's done.
Chris
I guess this is true, Do you know any ? (I need just one)
They unfortunately don't say how they are done. they cost about 300EUR though.
Martial
Don't digitise the absolute sensor signal then differentiate the digital value.
Get the sensor's analogue signal, feed it to one ADC for the altitude.
Get the sensor's analogue signal, differentiate it with a simple RC, then amplify that differential and feed it to a second ADC for the variometer.
Yes, that helps getting rid of the hires ADC. I can probably use the on board ADC of the Atmel MCU that way.
Any idea for a usable Pressure sensor ?
Martial
kryten_droid schrieb:
The Motorola sensors can be found at:
Average $7 each in quantity, IIRC.
and Sensym, now part of honeywell, can be found at:
Chris
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