Amp options for remote apps

Using Arduino Project Guidance
#1

I have 4 small DC signals (500 mV max) to capture with analogRead in a logger (field) application.

My sensor provides single supply voltage only.

I have been playing with the LM324 quad without success trying to amplify my signal with 5V from Arduino. Regardless, prototyping space is at a premium and I don't think the 12-16 resistors needed to configure single supply voltage amplification for four channels will fit on my shield. I'm thinking it will be a mess.

I'm looking for op-amp alternatives, or ways to increase Arduino's sensitivity. I'm currently using the 1.1V reference on the AVR chip for my voltage readings. Is it possible to provide a smaller reference voltage with a divider or voltage regulator as an alternative to amplification?

#2

You can put a refernce voltage into the AREF pin of your Arduino using a voltage divider (trimpot?).

Set the reference referring to this page.

With such low values you may need to look at some filtering for noise.

#3

Arduino are you using? Some (not the Uno) have internal amplifiers.

...R

#4

The board is a Diavolino, essentially a Duemilanove with a 328.

I see in the documentation for analogReference(type) that an external AREF can be set between 0 and 5V.

In this thread it is made clear that the Arduino documentation is incorrect in that AREF cannot be below 1V according to the ATmega328P data sheet . http://forum.arduino.cc/index.php/topic,53537.0.html

Back to square 1. Some kind of amp. Anny reccommendations for this application?

#5

Post the circuit for the lm324 that you have been using (without success) so we can give some advice on resurrecting that.

#6

Will this be good enough:

#7

Here is what I'm trying to do:

That Adafruit breakout might be just the thing for me thanks liudr.

#8

generally the voltage divider you have connected between what seems to be input and gnd is connected to plus instead of input. I just realised there was more of the picture then it shows on my screen, but it's still the same outcome. the input is still connected to noninverted opamp input. You could use the same divider for more opamps, especially if you connect a capacitor to ground at the divider's output. However this circuit might still not work, since the divider will set the middle voltage the amp will use for reference. since you measure 0.6V you need a divider voltage under that. One suitable divider is 1k to vcc and 100ohms to gnd for a reference of 0.45V. You can use a voltage divider calculator to find out. So now you have 0.45V for a zero output, and your signal is 0.6 which means the amp sees 0.15V as such a 10 gain amp will result in 1.5V output. The opamp gain formula can be used to calculate the feedback resistances.

Some more opamp design requirements are: one capacitor between + and ground on the opamp IC for stability and connecting unused opamps (-) input to output and ground so that they do not oscillate.

I hope this is not too hard to follow, it's hard to tell how terrible it is written.

#9