Mapping Floats

@ryano085

Is this what you are trying to do?
https://forum.arduino.cc/index.php?topic=3922.0

float mapfloat(float x, float in_min, float in_max, float out_min, float out_max)
{
 return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

@robotbuilder

Hi Robotbuilder, thanks for your speedy reply, Because i am new to electronics and programming in general i have never seen return been used in a map function and it blows my mind lol.. however i have been working on it and this appears to have worked. i basiicaly multiplied the temp by 100.

Foe those whole are sensitive to bad coding look away!!

void loop() {
//////// DHT ////////////////////////////////
float T = dht.readTemperature(); // Read temperature in Celsius.
float sum = 0.97;
int multi = 100;
float Tsum = T*sum;
int TMsum = Tsum*multi;
Serial.print("Temp = ");
Serial.println(TMsum);
///////////////////////// DHT ///////////////

//////// PWM FREQ //////////////////////////
float fan = map (TMsum, 2100, 2500, 40, 255);
if(Tsum > 25){pwmWrite(pwm,255);} // must use if/else if/ and else or will not work properly.
else if(Tsum < 21){pwmWrite(pwm,40);}
else {pwmWrite(pwm,fan);}
delay(500);
Serial.print("PWM out = ");
Serial.println(fan);
/////////////////////// PWM FREQ ///////////

any advice would help, even just to  clean it up.

@ryano085 The map function only does integer arithmetic https://www.arduino.cc/reference/en/language/functions/math/map/    hence the reason for @robotBuilder suggesting a floating point function to use instead.

@ryano085

Hi Robotbuilder, thanks for your speedy reply, Because i am new to electronics and programming in general i have never seen return been used in a map function and it blows my mind lol.. however i have been working on it and this appears to have worked. i basiicaly multiplied the temp by 100.

Foe those whole are sensitive to bad coding look away!!

It is bad coding if you don't know how it works.  Multiplying by 100 is essentially moving the decimal point although I would have to look at your code again when I get time to see exactly what you have done.

map() is a function with its own return if you look at it in the include file.  Programmers however write their own functions,  as well as using functions written by other programmers. Essentially you are adding your own commands to your program when you write your own functions. The map() function comes with the Arduino c++ but you could just as easily written it yourself.

If you want 500 outputs between 21 and 25 they will be floats with increments of .008

21.000  21.008  21.016 and so on up to 25.000

To use the floatMap() function or any other function you just type it outside the loop.

float mapfloat(float x, float in_min, float in_max, float out_min, float out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

void loop() {
  //////// DHT ////////////////////////////////
  float T = dht.readTemperature(); // Read temperature in Celsius.
  float sum = 0.97;
  float Tsum = T*sum;
  Serial.println(Tsum);
  ///////////////////////// DHT ///////////////

  //////// PWM FREQ //////////////////////////
  
  float fan = mapfloat (Tsum, 21.00, 25.00, 40.00, 255.00);  // <---- changed here
  
  if(Tsum > 25){pwmWrite(pwm,255);} // must use if/else if/ and else or will not work properly.
  else if(Tsum < 21){pwmWrite(pwm,40);}
  else {pwmWrite(pwm,fan);}
  delay(500);
  Serial.println(fan);
  /////////////////////// PWM FREQ ///////////

@robotbuilder

ahh i see, thats interesting i can do it without the map function, ie doing your own math but the map just makes it much easier! so now i got a PWM decimal place on the serial monitor and cleaned up a couple % memory. thanks for your help!!