ULN2003 based controller module for stepper motor

Using Arduino General Electronics
#1

I bought the following stepper motor with a ULN2003 based controller module and I am trying to get my head around how the darlingtons in the ULN2003 chip are arranged in a H-bridge for each stepper motor coil.

I have looked at the datasheet (http://cdselectronics.com/kits/uln2003.PDF

It shows the elements in the chip as diodes with 1 input and 1 output.

How do you get a H-bridge from a diode?

#2

Yes, you are correct! Did you have a question though?

#3

MarkT:
Yes, you are correct! Did you have a question though?

Sorry I was trying to get a web link to my attachments so I could show them inline.....not possible though.
Just linked the images externally.

#4

Ah, I see you've updated the original post from its austere initial version! I can understand
your confusion - there are no H-bridges, this is a unipolar motor and driver, there are 4 individual coils
sharing a common return. You only need current in one coil at a time (or two, depending on wave-mode
or full-step mode), and the current direction doesn't reverse.

Internally such a 5-wire motor is a 6-wire motor with the two centre-taps commoned.

#5

MarkT:
Ah, I see you’ve updated the original post from its austere initial version! I can understand
your confusion - there are no H-bridges, this is a unipolar motor and driver, there are 4 individual coils
sharing a common return. You only need current in one coil at a time (or two, depending on wave-mode
or full-step mode), and the current direction doesn’t reverse.

Internally such a 5-wire motor is a 6-wire motor with the two centre-taps commoned.

So with this driver module I take it you can’t do reverse steps?
I believe you can also use 5 wire stepper motors as a bipolar stepper if you wish?

#6

Yes you can do reverse steps. You are confusing the fact that current can flow in different directions
at different times in a coil with the notion of stepping. Both this and bipolar motors step between
states, 4 full steps per electrical cycle. In a unipolar motor each step is a separate coil energized,
in a bipolar motor only two coils, but each has two polarities, so 4 states again.

#7

I get it now. It is some what similar to multiplexing LEDs in an array.

#8

There are 4 (sets of) coils. One of the wires (the red one?) is wired to one end of all coils. The other end of each coil is wired to one of the other 4 wires.
Connecting any of those other 4 wires to ground activates the corresponding coil. By activating the coils in alternating patterns, you control the movement of the motor.

#9