how to invert input from sensor?

antoteipe

hello, beautiful people.

I'm working with an ultrasonic proximity sensor from which I get values that range from 0 to 200, and are directly proportional to the distance the object measured by the sensor is from it, in centimeters. if an object touches the sensor, the value measured is 0.

I would like to invert this connection: instead of a directly proportional input, an inversely proportional one, from which I get bigger values the closer the object is to the sensor. how could I achieve this?

kfrajer

Question: 200 is in actual distance units? If 200 is the max value then you could do

final int MINVAL=0;
final int MAXVAL=200;

final int NEW_MINVAL=0;
final int NEW_MAXVAL=200;

float invPropValue=map(inSensor,MINVAL,MAXVAL,NEW_MINVAL,NEW_MAXVAL); 

So if the object is close to the sensor, let's say at zero, invPropValue will be 200.

Kf

antoteipe

I think you meant

final int MINVAL=0;
final int MAXVAL=200;

final int NEW_MINVAL=200; // these two
final int NEW_MAXVAL=0; // being switched

Anyway, that worked for me!! Thank you :bz

kfrajer

My mistake. You are right!

Kf

jeremydouglass

Or, to hardcode it:

float invPropValue=200-inSensor;

map() is flexible in the general case, but a bit overkill for a zero-max inversion -- at least, overkill if performance is an issue. Just subtract and you are done.