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How to make a mathematical model from coordinates?

Hello,

I am really not very good with math. I am a construction worker! I did college math up to calculus.... but over the years, I totally lost it all. And besides I was always bad at math problems. But today, it caught up with me... LOL! I hope someone can help me.

In my spare time I am fiddling around with proximity sensors. I have a proximity sensor that accepts 135 steps of voltage (from 0 to 5V). For example, at 0 volts, I am at step 135. At 2.5 volts I am at step 67.6. At 0 steps I am 5V. I rather work with steps instead of voltage. Therefore, when I am at step 135, the sensor is able to detect an object 0 inches away. When I am down at step 0, the sensor is able to detect an object at 135" away which is the maximum distance. So as you can see the higher the steps, the shorter the distance an object can be detected by the sensor.The lower the steps the further the object can be detected by the sensor. The problem is that the relation is not linear, its exponential????

Therefore I need to make a relation between the number of steps and inches. Please view attachment for an example of the curve set by the steps vs the distance!

Here are some definite coordinates that I measured:

(0, 120)

(10,75)

(35,40)

(70,15)

My question is, how can I develop a mathematical model (formula) so that just by looking at a step value I would be able to calculate the respective distance without using the figure of the curve?

Thank you all for your help.

Re: How to make a mathematical model from coordinates?

I know nothing about such sensors, but I suspect they work by emitting an EM field, and as such the curve would more closely follow that of an inverse square, as given by the inverse square law of radiation.

Re: How to make a mathematical model from coordinates?

you lost me!

If I have 55 steps.. whats my inches??? don't look at the graph!!!