Help with A/D math!

[dbodenheimer]

Hi all,

I am building a small system to read a laser distance finder. This sensor outputs a 0-10 volt signal based on the distance from the object.
I am reducing the voltage to 0-5v with a voltage divider so that i get 0-5 v to AD0 on my PIC16F876.

Here are some examples of the data I'm getting back

Distance AD count
42.9 820
36.3 675
33.3 600
19.7 270
11.2 60

What i need to do is come up with a formula to convert the A/D readings into distance. So far I am failing miserably! The sensor can be adjusted to select where 0 is in distance and where 10v is. I currently have it set so that 6" is 0v and 50" is 10V I figure that I will have to provide a calibration routine that samples a near point (known distance) and a far point (known distance).

I REALLY need help with the math here to make this silly thing work.

Thanks in Advance,

Dave

[Acetronics2]

Hi, Dave

You can try :

distance = 8573 + 41*AdResult + ( AdResult / 2 )

with Distance ( use a WORD ) = 1000 * actual distance in " ...

Alain

PS; SURE it is a laser distance finder ??? I'd Better bet a laser pointer on a U.Sonic distance finder ... overall if measuring as short as 6" ... and no more than 40 or 50" ...

Alain

[dbodenheimer]

Alain,

Wow, works like a charm... now can you tell me how you got to those numbers? <grin>
I'm sure when I install this in the field I will have different numbers, so I will need to know how to recalculate.

You are a lifesaver!

Dave

[Acetronics2]

Alain,

Wow, works like a charm... now can you tell me how you got to those numbers? <GRIN>
I'm sure when I install this in the field I will have different numbers, so I will need to know how to recalculate.

You are a lifesaver!

Dave

Very simple, Dave ... no miracle !

just need to check what is PBP compatible , as an operation, and avoiding any overflow when calculating ...

Have a look here ...
http://curveexpert.webhop.net/

really a very handy tool

Alain

[dbodenheimer]

Got the tool. Yes it looks very handy!
Can you tell me the setup you used to calculate the data i sent?

I want to make sure i understand how to set things up

Thanks!

[lavenatti]

Enter data into “CurveExpert” chart:

X is distance, Y is A/D data

Select ‘Apply Fit”, select ‘Linear” from drop down menu.

A graph will pop up, press the ‘info’ button and you’ll get your equation and the coefficients to use.


I will never admit how long that took me to figure out.