28BYJ-48 & ULN2003 confusion

Using Arduino Motors, Mechanics, Power and CNC
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Hi Guys!

I just want to ask about this, it really bugs me.

how an arduino able to give signal in a pin without a ground?

I have tried to remove the ground wire from external battery to arduino and the motor still works.

the arduino is powered by my pc's usb.

Please see above image.

then this code
digitalWrite(STEPPER_PIN_1, HIGH);
digitalWrite(STEPPER_PIN_2, LOW);
digitalWrite(STEPPER_PIN_3, LOW);
digitalWrite(STEPPER_PIN_4, LOW);

The STEPPER_PIN_1 is set to high and all remaining pin are low.

how the ULN2003 able to detect that the pin is HIGH or LOW.

What im trying to say is just like a battery you need a positive and negative to have a current flow.

Please let me know if it is ambigous.

Thanks!

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Same way I think, that an led across high pin 1 and low pins 2, 3 or 4 would work. If you put a volt meter -ve into pin 2, 3 or 4 and the other probe in pin 1, it will read 5V.

So (and I am admittedly making a bit of a leap of faith here :wink: ) I'm thinking the ULN sees one pin as 5V high-ER than the others.

3

Why have you marked the line as Not Connected.

When I am using a 28BYJ I have a GND connection to my Arduino.

...R

4

Robin2:
Why have you marked the line as Not Connected.

Seems s/he found (perhaps accidentally) that it works without it, and is wondering why.

5

It works because of phantom powering via the signal lines - at least one is high and one low at
all times, so current flows through the transistors in the chip in odd unplanned ways, allowing
it to sort of work.

Don't ever do this, its a very good way to destroy a chip. No signal voltages should appear on
any pin of a chip before it is powered up. If this is unavoidable at least add a series resistor
of several kilohms to prevent large currents flowing and frying things permanently, or triggering
CMOS latchup.

6

But MarkT, his chip is powered with red and black from the battery, and the Arduino is powered on the usb. It's the (missing) ground between the 2 that OP is asking about.

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I think what @MarkT is saying is the GND current is flowing through unauthorized paths that were not designed for it.

...R

8

neiklot:
But MarkT, his chip is powered with red and black from the battery, and the Arduino is powered on the usb. It's the (missing) ground between the 2 that OP is asking about.

Yes, I know. The return currents from the 4 phase signals have to come back through the other
phase signals if there's no ground return.

9

Hello Guys!

Well I guess I should stick to connecting all grounds.

Thanks you for the responses

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august30:
Well I guess I should stick to connecting all grounds.

In this case yes, but be careful of such a sweeping statement. If you have one of those opto-isolatable relay boards, the ones with the JD-Vcc jumper, and you use external power for the relay coils, you want to keep the grounds un-connected.

11

neiklot:
In this case yes, but be careful of such a sweeping statement. If you have one of those opto-isolatable relay boards, the ones with the JD-Vcc jumper, and you use external power for the relay coils, you want to keep the grounds un-connected.

ya sorry about that..for this circuit only i need to connect grounds.

ofcourse isolated circuits must have different grounds.

Someone might make a mistake on that because of my comment.haha

Thanks!

12

Were the Arduino and ULN2003 module laying on a conductive surface?