# Calculation always returns 0 serial print

Dear Arduinoers,

I have a potentiometer 10kOhm which I want to use to control a stepper motors (Nema 17 1.8 deg bipolar) RPM. I am using a TB6600 stepper driver. Serial print reads 0 - 1023 from the potentiometer as expected.

When I try to calculate the RPM however the calculation returns 0.

``````int Pot = A1; // Input pin for the potentiometer.
int RPM; // Declares variable for RPM

void loop(){
RPM =(Pot/1023)*100
``````

This probably has to do with integer. I don’t want to make it floating though since I use it later on in a formulea to calculate the corresponding delay for the steppermotor to get the required RPM.

``````  //Enables the motor direction to move in a certain direction.
digitalWrite(dirPin,LOW);
//Makes 200 Pulses for making one full cycle (1.8 degree stepper).
for(int x = 0; x < 200; x++){
digitalWrite(stepPin,HIGH);
delayMicroseconds(10^6/((RPM/60)*200*2));
digitalWrite(stepPin,LOW);
delayMicroseconds(10^6/((RPM/60)*200*2));
``````

Any advice on how to fix this problem?!

Driez:

``````RPM = int(Pot/1023)*100
``````

How much is Pot/1023 converted to an integer? What changes if you first multiply before dividing first cast to a long, then multiply, and then divide?

Also change `int Pot = A1` to `const int Pot = A1` and you'll discover another bug.

And "10^6" doesn't mean what you think it means. Bitwise operators

Pieter

PieterP:
What changes if you first multiply before dividing?

You stand a good chance of discovering more weird stuff?

PieterP:
How much is Pot/1023 converted to an integer? What changes if you first multiply before dividing first cast to a long, then multiply, and then divide?

Also change `int Pot = A1` to `const int Pot = A1` and you'll discover another bug.

And "10^6" doesn't mean what you think it means. Bitwise operators

Pieter

Dear Pieter, I have worked around the int problem by changing the RPM calculation into the following formula which also caps my RPM at around 100 RPM.

``````RPM =(Pot/10);
``````

The Pot/1023 value will always be less then 1 so the integer makes it 0 that's why I knew it was an integer problem.

Why would I change the Pot to a const int?

Thank you, I changed 10^6 to 1000000

Try `RPM =(Pot * 100) / 1023;`

Try

``````RPM = (Pot * 100L) / 1023;
``````

As AWOL alluded to, log2(102,300+1) > 15.

PieterP:
Try

``````RPM = (Pot * 100L) / 1023;
``````

As AWOL alluded to, log2(102,300+1) > 15.

Oh! Forgot about that important little detail.

Cheers guys thanks a lot! I am almost there. Keep in mind it’s my first time programming anything so I really do appreciate all the help! I’ve been looking for this for more than 2 hours on google and forums.

Right now I have a setable RPM value with my potentiometer. I can continue to use this RPM to calculate the required corresponding delayMicroseconds. However I suspect there might be an easier way to do this?

Furthermore do I need to use an acceleration code or are the RPM’s low enough that this isn’t necessary (max 100RPM)?

This is my current code to drive the 17HS24-2104S nema 17 motor using the TB6600 stepper driver at 2A and 200 pulses per revolution.

I take the potentiometers input RPM and divide by 60 to convert it to RPS. Then I multiply this number by 10^6 (1000000) to convert seconds to microseconds. I divide by 200 to get the delay in microseconds per pulse and divide this by 2 to get the delay in microseconds per phase.

``````void loop(){
//Serial.print(Pot);
RPM =(Pot*100L)/1023;
Serial.print(RPM);
lcd.setCursor(0,0); //Defining position to write from first row, first column.
lcd.print ("RPM"); // Showing the letters RPM
lcd.setCursor(0,1); //Defining position to write from second row, first column.
lcd.print (RPM); // Showing current RPM value

//Enables the motor direction to move in a certain direction.
digitalWrite(dirPin,LOW);
//Makes 200 Pulses for making one full cycle (1.8 degree stepper).
for(int x = 0; x < 200; x++){
digitalWrite(stepPin,HIGH);
delayMicroseconds=((((RPM*1000000)/60)/200)/2);
//delayMicroseconds(500);
digitalWrite(stepPin,LOW);
delayMicroseconds=((((RPM*1000000)/60)/200)/2);
//delayMicroseconds(500);
``````

Driez:
Cheers guys thanks a lot! I am almost there. Keep in mind it’s my first time programming anything so I really do appreciate all the help! I’ve been looking for this for more than 2 hours on google and forums.

Right now I have a setable RPM value with my potentiometer. I can continue to use this RPM to calculate the required corresponding delayMicroseconds. However I suspect there might be an easier way to do this?

Furthermore do I need to use an acceleration code or are the RPM’s low enough that this isn’t necessary (max 100RPM)?

This is my current code to drive the 17HS24-2104S nema 17 motor using the TB6600 stepper driver at 2A and 200 pulses per revolution.

I take the potentiometers input RPM and divide by 60 to convert it to RPS. Then I multiply this number by 10^6 (1000000) to convert seconds to microseconds. I divide by 200 to get the delay in microseconds per pulse and divide this by 2 to get the delay in microseconds per phase.

``````void loop(){
``````

//Serial.print(Pot);
RPM =(Pot100L)/1023;
Serial.print(RPM);
lcd.setCursor(0,0); //Defining position to write from first row, first column.
lcd.print (“RPM”); // Showing the letters RPM
lcd.setCursor(0,1); //Defining position to write from second row, first column.
lcd.print (RPM); // Showing current RPM value

//Enables the motor direction to move in a certain direction.
digitalWrite(dirPin,LOW);
//Makes 200 Pulses for making one full cycle (1.8 degree stepper).
for(int x = 0; x < 200; x++){
digitalWrite(stepPin,HIGH);
delayMicroseconds=((((RPM
1000000)/60)/200)/2);
//delayMicroseconds(500);
digitalWrite(stepPin,LOW);
delayMicroseconds=((((RPM*1000000)/60)/200)/2);
//delayMicroseconds(500);

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