I don't know if this is the most relevant place to post this, so please forgive me if this is not the ideal location.
I stumbled across your schematic on YouTube, and it led me here to your site.
Here's the link so you know what I'm referring to.http://elabz.com/driving-a-bipolar-stepper-motor-with-arduino-and-uln2803ag/#more-362
I am a complete beginner in the electronics realm of things, and this being said have really struggled trying to get "Bi-Polar" Stepper motors running properly.
It seems to me, that this site is very active, and responsive, and I like that!!!
I spent some frustrating hours trying to run my motor off of my own design I made from some NPN Transistors (Sounds like one of your other comments from Kiran).
In this previous design everything seemed to work OK on low power (Arduino UNO 5V output), but of course this was without any usable torque on a much larger motor a friend let me borrow.
This motor was rated at 12V 1A, and figuring I could use an ATX 12V PC Power Supply, my results ended with burning up some of my NPN Transistors.
After implementing your design, I see some flaws in my own, but to take the corrective action to get my stuff working, I'm not confident in the corrective action that I think I need to take.
My only thought is that I would need a 12W (This seems massive) 12 Ohm resistor per leg of the coil... Is this correct???
Here's a basic diagram of my design without any resistors or diodes.
Since the image is awaiting approval, here's a link to it.http://wikiwiggs.web44.net/mystepperdesign.html
I've implemented the Bi-Polar driver based on the ULN2803A that you came up with, and I have to say that this was an easy to implement, after I saw your video, I went to mouser and purchased 10 of these chips, I just got them last night and was able to get a small motor running - Thank you.
As far as personal "style" goes, I like to figure out what I'm dealing with, in order that I am hopefully able to have a little bit of "gut-feel" when I'm doing something wrong.
So before I implemented your design using this chip, I spent some time poking around YouTube trying to find out more about the ULN2803A.
I found one that helped clarify to me what was really going on:
My conclusion was that these ULN Transistor arrays on it's simplest level can be thought of as a single NOT Gate per channel.
It helped me get confident, and I partially implemented your schematic design (only because of lack of time).
I left out the user buttons & LED's to control and indicate direction, instead I just changed my code on the Arduino side to see that I had control.
I used an old floppy stepper that I had in my arsenal as to hopefully match what you used on the video.
I since broke off a soldered connection (poor handling on my part), and used a stepper that I had ripped out of a scanner bed.
This motor worked in the same circuit design although it is rated at 8 ohms, the ¼ Watt 22 Ohm resistors provided enough pass through to let it at least step appropriately.
Thanks for the help, and thanks for awesome work & willingness to share it.