Use ULN2003 type stepper driver boards with only 2 breadboard cables

There are two cheap (0.30$) ULN2003 type stepper driver boards.
The cables from stepper motor nicely fit into the driver board connectors.
For both types of driver boards there are pins IN1-4, 5V and GND.

For the left board I did bend the 4 middle pins by 90°.
I did push those 4 pins into pins 2-5 of Arduino Uno directly.

I did push pins IN1-4 of right board directly into Arduino Uno pins 9-12.

I know that is not really safe to power stepper motors from Arduino 5V rail.
But I do this routinely without having seen issues.
At the monent I will loose an Uno or one of its pins I will stop that, and report here.
I drive the two stepper motors of “stepper PT camera system” that way for several days now:

I connected 5V and GND of left driver board with female/female connectors to ICSP pins 2 and 6.
I connected 5V and GND of right driver board with female/male connectors to 5V and GND on Uno.

I uploaded video that this works indeed:

FAIL(Forward Action In Life). You now understand why "I know that is not really safe to power stepper motors from Arduino 5V rail". If you are lucky your arduino is still OK! Use an external power supply. You watched the videos now you know some other lucky people. Manufacturers place specifications on what they make, it is up to the engineer to determine if the part will work in there application, reliability for most hobby engineers goes the way of the trash bin as does reading specification sheets. That gives them lots of practice debugging and trouble shooting. Try again and again you might get it working and you might be buying a lot of boards.

Good Luck & Have Fun!

Gil

gilshultz:
Manufacturers place specifications on what they make, it is up to the engineer to determine if the part will work in there application, [/color]

Please help me, which specifications exactly do you refer to?

Arduino Uno delivers 5V on 5V female connectors and on ICSP pin2.
What is the maximal current an Arduino Uno can deliver safely?

I use the ULN2003 drivers to drive two 28BYJ-48 stepper motors:

The maximal load is this scenario:

The bottom stepper has to turn 55.5g (upper stepper+70mm lens).
The upper stepper has to turn 19.1g 70mm lens.
Stepper maximal speed is 1step/ms.

Moving up lens from horizontal to vertical (90°) in 1024 half-steps without acceleration at 1step/ms should be maximal load.
Is there a way to compute the current the upper stepper will draw maximally?

Turning lower stepper 90° in 1s with lens in horizontal position should be maximal load.
Is there a way to compute the current the lower stepper will draw maximally?

Stepper motors draw the same current whether loaded or unloaded, moving or standing still. 5V 28BYJ-48 winding resistance is about 50Ω, so current with 5V will be 100mA, if using half stepping, 2 coils may be on at the same time, so double current (200mA).

JCA34F:
Stepper motors draw the same current whether loaded or unloaded, moving or standing still. 5V 28BYJ-48 winding resistance is about 50Ω, so current with 5V will be 100mA, if using half stepping, 2 coils may be on at the same time, so double current (200mA).

Thanks for the explanation, "Stepper motors draw the same current whether loaded or unloaded" eliminates to look into special scenarios.

So the question now is, whether Arduino 5V pin can deliver 200mA, the datasheet only states "DC Current for 3.3V Pin 50 mA", no statement on "DC Current for 5V pin":
https://store.arduino.cc/arduino-uno-rev3

HermannSW:
So the question now is, whether Arduino 5V pin can deliver 200mA, the datasheet only states "DC Current for 3.3V Pin 50 mA", no statement on "DC Current for 5V pin":

That 3.3volt/50mA statement is taken from an old version of the board where that supply came from the USB chip, and it is wrong for the rev3. Rev3 boards have a dedicated 3.3volt/150mA regulator.

Current capability of the 5volt pin depends on where it's coming from.

If on USB supply, the limitation is an inline 500mA polyfuse, to protect the PC/laptop USB port.
The Uno takes 50mA for itself, so about 450mA max is available.

If on external supply (DC socket or V-in), then max current depends on input voltage.
About the same as the USB socket with 7volt on the DC socket, but that drops to ~150mA with 12volt on the DC socket, because of the thermal limitations of the 5volt regulator (it gets hotter with a larger drop).
Leo..

Thank you for that detailed analysis!

Summary, in gerneral one has to do the calculation on what is safe to connect to Arduino 5V rail.
Powering my “stepper PT camera system” from USB powered Arduino 5V rail is safe!
(2×200mA < 450mA, just updated that thread with this information)

Wawa:
Current capability of the 5volt pin depends on where it’s coming from.

If on USB supply, the limitation is an inline 500mA polyfuse, to protect the PC/laptop USB port.
The Uno takes 50mA for itself, so about 450mA max is available.

JCA34F:
Stepper motors draw the same current whether loaded or unloaded, moving or standing still. 5V 28BYJ-48 winding resistance is about 50Ω, so current with 5V will be 100mA, if using half stepping, 2 coils may be on at the same time, so double current (200mA).