[En-Nut-Discussion] Need Analog Help

[Daniel Buergin]

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

> First question: What's your reference voltage? (So >
> what is connected to 
> AVRs AREF pin?)

The AREF Pin of the ATmega128 is connected to the
5V Pin of the ADC Header (Pin 2). I measured it 
with my Multimeter. 

> It seems your reference voltage is either lower than
3.799V or you'r 
> measuring with internal 2.56 Volt reference.

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.

> BTW: AFAIK the change of the output voltage of your
4115A is quite small 
> (if you try to measure atmospheric pressure) so you
perhaps want to use 
> an OpAmp to adjust the scaling of your measurement.

>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.

I think, i have to learn how to integrate a OpAmp...

Daniel  




		
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