I have a stepper motor which drives a linear unit. For references there is limit switch on one side.
If i load my programm on my atmega2560 and then i disconnect the usb cable from the computer and then press a start button -> referencing works perfect.
But if i dont disconnect the usb cable -> the programm doesnt recognice the limit switch -> it would destroy something if i wouldnt stop it.
Does anyone have a idea why that happens?
If necessary i can post my code here.
Thank you!
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Please post a schematic.
Please post an image of your project.
Please describe the problem better then you just did.
Schematics would likely tell.
You might be using the wrong I/O for the limit switch.
this is my code:
// Bibliotheken
#include <Bounce2.h>
//Konstanten
const int LED = 13;
const int Taster = 8;
const int Taster_Start = 2;
const int Endschalter_1 = 9;
// Define stepper motor connections and steps per revolution:
//Motor 1
#define dirPin_1 23
#define stepPin_1 25
#define enablePin_1 27
#define stepsPerRevolution 6400
//Tasterprellen unterdrücken
Bounce myButton1 = Bounce();
//Bounce myButton2 = Bounce();
//Setup
void setup() {
pinMode(LED, OUTPUT);
pinMode(Taster, INPUT_PULLUP);
pinMode(Taster_Start, INPUT_PULLUP);
myButton1.attach(Taster);
myButton1.interval(5); // 5ms zum Entprellen
//myButton2.attach(Endschalter_1);
//myButton2.interval(5); // 5ms zum Entprellen
//Stepper Motor
//Motor 1 (horizontale Achse)
pinMode(stepPin_1, OUTPUT);
pinMode(dirPin_1, OUTPUT);
pinMode(enablePin_1, OUTPUT);
}
//Endlosschleife
void loop() {
// Taster für Referenzierung abfragen
myButton1.update();
if (myButton1.fallingEdge()) {
digitalWrite(LED, HIGH);
digitalWrite(dirPin_1, LOW);
digitalWrite(enablePin_1, LOW); // Mit LOW enablen!
while (!digitalRead(Endschalter_1)) {
digitalWrite(stepPin_1, HIGH);
delayMicroseconds(100);
digitalWrite(stepPin_1, LOW);
delayMicroseconds(100);
}
digitalWrite(dirPin_1, HIGH);
for (int i = 0; i < 5 * stepsPerRevolution; i++) { // 2 Umdrehungen in die andere Richtung
digitalWrite(stepPin_1, HIGH);
delayMicroseconds(100);
digitalWrite(stepPin_1, LOW);
delayMicroseconds(100);
}
digitalWrite(enablePin_1, HIGH); // Mit LOW enablen!
digitalWrite(LED, LOW); //Referenzierung abgeschlossen -> LED ausschalten
}
}
this code works when i disconnect the usb cable
The schematic? The image of the project.
In the second pic you can see the limit switch and the stepper motor.
And in the first pic you can see the atmega2560 with the blue usb cable.
if i disconnect this blue cable everthing works fine. if i dont do that, then the programm doesnt recognize the limit switch.
and for the stepper motor, i have a stepper motor driver...
i know you can see more cables on the microconroller, but i dont use them at the moment (i want to controll 3 stepper motors with it)
i cant imagine why it doesnt work when i connect the microcontroller to the computer via the usb cable
Imagines. The power supply is insufficient? The grounds are not properly connected.
The "schematic" leaves a lot of information out.
And another power supply with the white cable. Maybe you made a ground problem. Try without that power supply. Or use a USB galvanic isolator.
Can you just try a tiny sketch that only reads and reports the state of the limit switch?
a7
I notice that on that last photograph the wires going to the limit switch terminals are just pushed through and are not soldered. This is the best way to make an intermittent / unreliable connection.
Solder them up please.
You seem to be not aware of the difference between a schematic and a photograph. If you truly don't know then ask and we can enlighten you.
Thanks! Yes the problem is a ground problem.
Is a USB galvanic isolator the best way to solve this problem?
because i think its not the best idea to disconnect the green/yellow cable from the 24V power suppy or from the power supply of my laptop.
Thanks! Yes now i know. The contacts of the limit switch are soldered. Its on the other side (not visible very well)
This works. With the switch is everything fine. But thank you!
The USB galvanic isolator do 2 things. It bricks the problem for ground loops AND it protect the USB from your PC/laptop for over current from outside. It isn't a bad choice to use in testing conditions.
GND isn't only the earth. Read this.
A good stepper driver (like Leadshine DM856 !!!! for fake) uses optical input (opto coupler) that in fact prevent for ground loops.
Edit: for the limit switch you can better switch to ground and use the internal pull up and a NC contact is better than NO. If the cable is broken by NO you never becomes the end point. By NC, if the cable is broken the end point is reached.
Thanks!
ok. yes my stepper drivers are very very cheap ones 
You can brake the ground loop by using your own opto couplers like PC817/PC827/PC847.
Just to note that I would disagree with the solution offered by @buckfast_beekeeper .
You do not need galvanic isolation on your USB, in fact these are very expensive and would require another power supply.
Ground loops in this context are not a thing, these are more of a problem with audio circuits.
All you need to do is to connect a wire between the ground on your power supply to the ground on the Arduino.
Not correct. You don't need another power supply. What is the most expensive? The USB port of your PC of the galvanic isolation? Do you have a galvanic isolator? I have few without problems.
Ground loops are not only in audio a problem. They are everywhere but are not always a big problem.
Well let's disagree on this one. But just a point, how much actually experience do you have?
I have been using microprocessors to make projects since 1975.
Thanks!
In this case you mean with ground the yellow/green cable which goes to the 24V power supply?
I go to the 24V power supply with one black (L1: 230V), on blue (N) and the yellow/green ground (I m not sure if thats called ground in english).
