different voltaje a/d sensors

[RodSTAR]

Hello grls & guys
i have a pic18f4431 (obvious 5v) and i want to A/D at the same time:
1.- a 0-3,3v device (accelerometer),
2.- a 0-3,0v device (gyro) and
3.- a 0-5,0v device (thermsistor)

of course i have o problem on power supplying them, just voltage regulators & stuff, my problem is to measure the full range of each.

it seems VREF works just for all a/d inputs at a time?
is it possible?
if possible, how should i circuit it?

thx grls & guys

[mackrackit]

It may not be the best solution but when I run into this type of thing I will scale the higher voltages down with a voltage divider so they all match.

The 0 to 5 volt sensor is now a 0 to 3.

[dhouston]

I don't understand the problem. If you are using 5V to power the PIC, you can also use it for AVdd. You will get the full range of all 3 sensors, you will merely lose resolution on the 3.3V & 3.0V sensors. If you want to maximize resolution, use op amps setup for DC gain to promote the 3.0V & 3.3V sensors.

[ScaleRobotics]

I think he wants full resolution of the A/D converter at 3.3v as well as 5.0v.

Darrell had a real nice 10 to 16 bit selectable over sample routine. It seems the sites.picbasic.net site is having some issues, so right now you can not download it from there. It was here: http://sites.picbasic.net/index.php?...d=70&pageid=27 and it was called DT_Analog.pbp

By going to 11 bit over sampling, you would effectively get the resolution back for your 3.3v devices, and no extra hardware. It does slow your sampling time a tiny "bit" for the extra bit.

Here is the speed

[RodSTAR]

As PIC is 5v I was thinking to transform electrically all sensors to ranges to 0-5v with a "magical IC" that outputs an analog voltaje (not digital) proportional to the input.

For example if a 3,3v device (accelerometer, sensor) outputs 1,65v (50% of 3,3v), then this "magical IC" will recive 1,65v and output 2,5v (50% of 5v).- Aswell if in another channel or other IC configured to transform 0-3v to 0-5v (if sensor says 1,5v my PIC will receive 2,5v). Of course I think this IC should be circuited for matching the desired specific voltaje range

Maybe those "magical" IC's are OpAmps, as dhouston (thx!) commented. Can OpAmps make that function?

"Realtime" processing is critical, so multisampling solution suggested by scalerobotics (thx!)is definitely not an option to my application. Interesting for another app anyway.

And to shrink voltaje as mackrackit suggested (thx!) it would limit "natural" analog resolution. I prefer to amplify a voltaje than shrinking it. And I hope an Operational Amplifier (OpAmp) does that.

So: Can OpAmps make that function?

Thank you very much for your attention !

[ScaleRobotics]

Sounds good. Certainly a lot of options.

96.8 millionths of a second can seem like an eternity.

[dhouston]

So: Can OpAmps make that function?

See the Non-Inverting Amplifier in http://www.national.com/an/AN/AN-31.pdf.