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Topic: How to increase resolution of analog input (Problem Solved - Thanks) (Read 2872 times) previous topic - next topic

CrossRoads

R3/R4 - yes, this just sets a DC signal for you to multiply.
R1  sensor
R2 - gain control.

Could also put your part in place of R4, use R3 of 100K and set R1/R2 for gain of ~20 (10K, 200K)
Vin then = 5V*(3k/103K) = .145mV, Vout = 2.912
Vin = 5V*(5K/105) = .238mV, Vout = 4.76

Math is  straightforward, find a combination that works with the parts you have.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

fkeel


while I will be needing thos opamps ... I still ended up doing some fun things with my sensors :-D ...
check it out: http://arduino.cc/forum/index.php/topic,53357.0.html
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

CrossRoads

In that case, take the voltage out from the original ciruit, offset it down in DC level and then add some more gain for wider response.
What you need is a non-inverting summing amplifier
http://masteringelectronicsdesign.com/how-to-derive-the-summing-amplifier-transfer-function/
but you need a -2.5v source to add in.

maybe something like this
http://www.maxim-ic.com/datasheet/index.mvp/id/1728/t/al
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

fkeel


Hey CrossRoads

I only saw your last reply right now... I dont understand what your saying - What case are you referring to?

Ok, I sort of understand the content of the first link, however I dont quite understand what benefit that has over this first circuit you suggested.  The second link points to an elaborate "voltage inverter"?

Why would I want to do it this way?

****

Anyway, I got myself some of the opamps & capacitors you originally suggested. I hope to get around testing this soon, though I am sort of swamped with university stuff at the moment. The capacitors are just add in parellel between Voltage in & Ground, correct? Their function is basically a low pass filter and the 0.1mf capacitor filters higher frequency signals, while the 1mf prevents noise with slightly lower frequency?

(sorry if I'm asking really simple/silly questions I just have no knowledge of electronics whatsoever, and I just want to double check that I actually understand what I am doing.)

Thanks for your help so far, and any additional help you can offer.

Cheers

P.
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

CrossRoads

I don't know anymore, been too long, need to review what it was you were doing.
I think I was suggesting a way to change the DC level so your ac signal could be amplified more so the ADC could take samples over a wider range.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

fkeel

got it. makes sense.

if I want to use a 0.1mf and 1mf capacitor to reduce noise, where would I put them, assuming I am using the set up you suggested?
( http://arduino.cc/forum/index.php?action=dlattach;topic=53242.0;attach=883;image )

To my best understanding, I connect them between +5v and ground and I connect them in parallel - so even before R3. However intuitivly I would connect them after R2.

Could you give me a pointer as to where to add them to your schematic?

Thanks

p.
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

CrossRoads

Put them across the noise source going into the op amp, so across the +in or the -in terminal to ground, whichever side your sensor goes in.
Stop the noise before it gets amplified.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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