having strange behavior with motor shield and steppers. when i'm trying to make onestep, motor just makes some high-frequent noise, but when i add Serial.println for debugging, it moves as intended.

what is going on here?

here is an example:

#include AFMotor.h //dunno how to put angle brackets here

AF_Stepper lrM(48, 1);

void rightStep() {  
void leftStep() {  

void setup() {

void loop() {

2 Answers 2


My guess is Serial.println adds additional delay so stepper motor can react. Without it changes are way too fast (= high frequency noise) to do whole step.

Try to add delay(1); or more into the main loop.

  • i thought that if onestep function is blocking, it would be ok, but it appeared that i need delay(10) so that motor can run. thank you! Jul 14, 2016 at 19:05
  • Method step contains delays, but there are no delays in onestep (at least not obvious ones).
    – KIIV
    Jul 14, 2016 at 19:09

When you have a Serial print statement running really quickly the output buffer will fill up and the print command will have to wait for there to be room; That causes the command to take a substantial amount of time to complete.

When the statement is missing, you loop probably runs a few hundred times faster than without it (depending on how long onestep takes), probably fast enough that the physical motor can not keep up.

Try adding a delay of a few milliseconds or some kind of rate limiting to the program and then see how much of a difference serial.println makes.

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