[En-Nut-Discussion] Need Analog Help

[Ole Reinhardt]

> I've got it working, but i'am not sure if it's
> ok...

Fine... AREF settig should work. But although I wrote the code I never 
tested this setting. Normaly I use INTERNAL_256 or AVCC.

> Maybe i explained it a little bit wrong. The sensor
> is powerd by 5V form the ADC Header (Pin 3, Analog
> Supply). 
> And i measured the 3.799V at the Outputpin of the
> Sensor. 
> So this is what i should measure with my Program.  
> 
> And, after removing ADCSetRef(AREF), it works. 
> I measure around 945milibar and with another digital
> Barometer, i get 948milibar. 
> So this is not bad.

Hell, where are you living? You will have realy bad weather :-)

>>From the Datasheet:
> 
> - Pressure Range : 15 - 115 kPa
> - Full Scale Span: 4.590 V (at 5.1V)
> - Sensitivity    : 45.9 mV/kPa
> 
> I'am not a A/D-Profi right now ;-) But i think you are
> right. 
> 45.9mv/kPa means 4.59mv/milibar. And when i calculate
> right,
> i have 5V / 1023 means 4.8mV/tick.

Ok, if you'r ok to measure around one milibar per tick this will be ok 
for you. Otherwise you should think about an amplification of five (for 
normal weather conditions). In this case you also need to adjust the 
offset voltage. Of course you should also use a high inpedance input... 
This will need all in all three or for OpAmps.

This is a schemtic with only two OpAmps, but with a measuring range from 
0-10V.

http://www.davidbray.org/onewire/baro20.html

This one is more complete:

http://www.qsl.net/ok2xdx/Barometr/BarometrEN.html

Also interesting:

http://www.sparkfun.com/tutorial/WeBBS/WeBBS-Final%20Report.pdf

Another one:

http://www.qsl.net/ok2xdx/Altimeter/altimeter.html

Hope this will help...

Best regards,

Ole

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