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Topic starter
2020-06-08 3:56 pm
Hi all,
i am new to the forum and electronics and wish to start off by asking a question about mapping a float value. i am under going a small project one which will involve an Arduino nano, DHT11, TM1637 & a 4-pin PC fan (ARTIC F14 25Khz) i have PWM.h changing the Arduino frequency.
I am familiar with the map function, albeit at a basic level. The aim of this project is to test the temperature, display it, map the temperature value to a PWM pin, then drive the fan (i assume there is a motor driver within the F14?? as i am not using one), which is powered by 12V. This project operates fine on the surface.
However, when i print the PWM values to the monitor i see that the PWM value does not change until the temperature fills to a whole number. i will include a snippet of the code as it is long.
my expectations included a smooth map from 21.00c - 25.00c in a effect giving me 500 speed variations.
Am a making sense or is this all waffle?
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 = map (Tsum, 21.00, 25.00, 40.00, 255.00);
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 ///////////
The "sum" is my crude way of calibrating the sensor with my home thermostat.
2020-06-08 4:33 pm
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; }
Topic starter
2020-06-08 5:45 pm
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.
2020-06-08 6:00 pm
@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.
Pat Wicker (Portland, OR, USA)
2020-06-08 9:22 pm
Topic starter
2020-06-09 9:19 am
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!!