Math Problem

[erice1984]

Wow, you mention that and I look at the gauge that the sender was supposed to work with and they did that!

[erice1984]

So I looked at the resistor that was used, its 510

It brings the change in resistance per degree down to
3 ohm from 100-150
2 ohm from 151-200
1 ohm from 201-250

Isnt that crazy.

[erice1984]

I am going to use an op amp to get me full range of my 0-5v scale instead of this 0-1v stuff... would that limit the signal from "bouncing" around?

[mister_e]

You could filter your signal in hardware, or in software (averaging results). I tend to use hardware in many case as it's just a matter to add a capacitor or any kind of Low-Pass filter. On the other hand, a combination of both is also good depending how fancy you want it.

[erice1984]

interesting, I have heard about the capacitor trick. How would it be done "averaging" in software?

[rsocor01]

Erice1984,
Looking at the EXCEL graph that you have posted it seems like a second degree polinomial will fit nicely. A formula of the form Y(X)=a*(X^2) + b will work. The EXCEL trendline will give a value for a and b in the above formula. Then, round this numbers up and you should have a good approximation for your graph. I am writing this reply from my cell phone so I don't have EXCEL with me at this moment to show you what it might look like.
Give it a try. If you have any problems, let us know.

Robert

[Darrel Taylor]

How would it be done "averaging" in software?

Here's one possible way.
http://www.picbasic.co.uk/forum/show...3267#post13267

Although I never did hear back from ANYONE.
I have used it myself since that post.
No problems found.

It's based on my original Averaging routines ...

Averaging 16 bit values without using 32 bit math?
http://www.pbpgroup.com/modules/wfse...hp?articleid=7

HTH,

[erice1984]

I updated the spreadsheet, feel free to take a look

http://www.drivearu.com/Electronics/...thermistor.xls

I am pretty confidant in this one, no exponents which is nice, and I looked at other automotive temperature gauges and they are showing +/- 7 degrees on theirs.