Variometer for RC Sailplane

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  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


Re: Variometer for RC Sailplane

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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.

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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



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Re: Variometer for RC Sailplane


Chris Quayle schrieb:
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I guess this is true, Do you know any ? (I need just one)

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They unfortunately don't say how they are done. they cost about 300EUR
though.

Martial


Re: Variometer for RC Sailplane
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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.




Re: Variometer for RC Sailplane
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:
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Re: Variometer for RC Sailplane
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The Motorola sensors can be found at:

http://e-www.motorola.com/webapp/sps/site/taxonomy.jsp?nodeId02%WcbfCjB1yZQ3tKGF8716

Average $7 each in quantity, IIRC.

and Sensym, now part of honeywell, can be found at:

http://content.honeywell.com/sensing/prodinfo/pressure_all

Chris

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