I just use two separate power supplies plugged into the same power strip. I think spreading the wiring apart helped also a bit to get rid of unwanted signals. Next time I might look for shielded wires. My setup still needs some more work because the pen is hanging below center and not all components are attached firmly. I also used wood for the parts because I do not have a 3d printer at hand. I was not looking for the perfect build, but I just wanted to see this cool machine in action. 🙂
Here are two photos of the still unfinished build:
https://my.hidrive.com/share/3k8sqsboii#$/

Nice, thank you for the update :). Do you mind sharing what the solution was? I always love receiving pics of people builds too :).

I installed everything and it is working perfectly. The two separate power supplies seem to work. Thank you for your kind support!

This is getting to be beyond my realm of expertise, but depending on your power supplies it might be ok, or not :). If both your power supplies are truly grounded and on the same power supply, I think they indeed share the same ground. But it’s also possible they each provide a floating ground that is different from each other and that will definitely mess things up.

The best way to be sure is to have just one power supply and share its one ground to all components downstream.

Thank you for taking time to explain this in more detail, I appreciate it. I did not know about the shared ground, good to know. If I use two separate power supplies, but they are both plugged into the same power strip, would everything share the same ground? Or does it have to be one shared power supply?

I’m not sure how closely you followed the circuit diagram, but it’s essential that these things all be grounded to the same ground. You shouldn’t use another power supply for the Pi as it implies it’s on a different ground. That would definitely explain it. I pointed to this stepper driver as I found it to have a good default position for the potentiometer, tuning it can be tricky. And yes twisting the wires is a way to avoid interferences that would result in erratic stepping. But really the ground is first and foremost here, the components all need to share it. I hope this helps.

I think I found the issues:
* I twisted the cables as suggested. That seemed to improve it a little bit.
* I turned up the potentiometer to increase the current. I have a Nema 17 with 1.5A.
* I had the Raspberry hooked up to a charger. I changed that to the official power supply from Raspberry.
The stuttering is as good as gone. It rarely misses a step now. I still have to see if there is enough power.

Hey Steven,

I don’t know how the PlottyBot image interacts with the ability Raspios has to load network information on the boot partition, but I’m guessing poorly :). I’d definitely re-write that SD card without your wifi preloaded.

Then I’d boot up the Pi, give it a good 10 minutes as it installs a bunch of stuff initially. And it’ll span its own wifi network called “PlottyBot”. You can connect to that. The one thing that kind of sucks when you’re connected to it this way, it that it has no internet connectivity and neither does your iPad. They’re just in their own little network that’s not on the internet. But you can still use the machine and have it draw just fine. Optionally, you don’t have to but it makes life a little easier, you can indeed have it scan for wifi network and connect to that. When you do that PlottyBot will remember that network next time it boots up and connect to it. But if you took it somewhere else not in range, it would revert back to spanning its own network so you can always use it.

This “connect if you can or span your own wifi” mechanism is very involved and intricate. And it likely doesn’t play well with the boot partition preload.

So I think starting fresh on that SD card is your next best step. I hope this helps :). Take care.

That does really sound like bad wiring or a bad driver. I’d look at the ground in particular but it’s hard to say for certain.

Hi Ben,
I believe I did not make myself clear in my previous post on December 10th, but I can not connect to the Raspberry Pi Zero W through ssh no matter what i try. I have checked off the option to add SSH and also added my Wifi ssid and psswd information within the Raspberry Pi Imager. I also skipped those options in the imager and added manually the the blank ssh file and the wpa_supplicant.conf in the boot folder after the image is finished being created just to see if that would make a difference. Also when I do get access to the Plottybot webpage do i have to choose a wifi network from the Wifi Setup window in the top right corner? and I do get the same error code maybe 50% of the time and besides that I just think its some kind of connection issue, I see the connection on my iPhone or iPad going from No Internet Connection to connected every minute or so. I realize these errors can be difficult to resolve so if you do not have the time I completely understand.
Thanks Ben I appreciate it

Hello Ben,
I hope you are doing well, I will try all of that tonight.
Thank you Ben

It does look like I have a bug, I forgot to declare ht_penstrokes_mutex in that function the error references (ht_penstrokes_processing).

Since you’re SSH’d in, it might be quickest to just edit the Python, find that function (ht_penstrokes_processing) and add the variable ht_penstrokes_mutex to the list of globals defined at the very top of that function.

This omission is bizarre, seems like my tests should have failed too.

As for the networking, Plottybot does something weird in spanning its own AP unless you connect it to your local network. This mechanism works well here at home but it’s just one guy testing on a few network setups so it’s entirely possible there’s an interaction with your home network that doesn’t work well. Maybe you can leave it not connected to your home setup and test by connecting to the “PlottyBot” network it spans. That would remove some variables.

I hope this helps, I’ll endeavor to fix this variable in the code. Sorry you ran into that bug.

Hi Ben, how are you doing? I just wanted to let you know where I am in the process. I do not get the error message I sent last night and I did get the gondola to try to draw out a letter, it was actually the fifth letter that i wrote in the Handwriting / Typewriting section. I believe there may be some sort of communication issue between my inputs from the iPad to the Pi and vise versa. I have used these Pi’s before and SSH to them but Putty which I use for SSH can not find the Pi, I also use Angry IP Scanner and Find My Pi but neither one can find it. I also log into my router and do not see PlottyBot. I’m not sure but is it possible that i need to make the Pi use a static IP address as I have done with other Raspberry Pi’s. I will continue to figure out what I am doing wrong. Thank you again Ben for all your help.

It looks like I may have a bug 🙂

I’ll look into it, but in the meantime, you should be able to use the handwriting stuff without the “live” checkbox. It should render in the draw box up top, and you can hit the “play” button to have the machine draw it. And you probably need to reboot the Pi to relaunch the Python process.

I’ll let you know what I find, thanks for the report and sorry about the bug.

Hello again Ben, I have everything setup and imputed the distance for the calibration, I first tried the Draw section but couldn’t get anything to draw ( I was using an iPad ) I the tried the handwriting section with the live tab checked ( I believe that’s what it’s called ) but there was no response from the motors or pen. I then went to the Mechanics section and tried Pen Up , and Pen Down which both responded. I also got this Error code below. Is there anything offhand Yo can think of that may be the problem besides of course the Error code which I will try to look into with my limited knowledge of coding.
• Error
Exception in thread Thread-4: Traceback (most recent call last): File “/us/lib/python3.9/threading py”, line 954, in _bootstrap_inner self.run() File
“/us/lib/python3.9/threading py”, line 892, in run self. _target(*self._args, **self. _kwargs) File
“/us/local/bin/plottybot.py”, line 2431, in ht_penstrokes_processing while ht_penstrokes_mutex==True: UnboundLocalError: local variable ‘ht_penstrokes_mutex referenced before assignment

I’m glad it was simple. Checking wiring it’s like proofreading, if your eyes didn’t catch a mistake the fist time, they’ll miss it the next 10 times as well.

Hi Ben, it turns out it was a simple wiring mistake the right motor is now working fine I don’t know how I missed it. I will calibrate it tonight thank you Ben.

Thank you for replying so fast Ben and thank you for this project. Yes the left side motor works fine, I will swap out the left motor tomorrow and let you know what happens. Thanks Ben

Hi Steven,

I find it really hard to believe that the SD card is the culprit. There are lots of failure modes with stepper motors that will result in them humming without moving. It’s good to know you’ve eliminated the driver by trying other ones. Does your left side motor work? How easy would it be to swap with that one to see if the problem follows the motor, or the pins on the Pi?

Hi CJ i’ve ran into the same problem as you have with only hearing a faint Stepper Motor noise coming from the (Right side) when trying the Test Top Stepper Motor. I have tried 3 of the 5pcs KOOBOOK A3967 EasyDrivers, and have tried another Stepper Motor and made sure wiring was all correct. I first flashed a Sandusky EDGE 8GB and then flashed a Samsung EVO 64GB. My question is which SD card did you use. Thank you.

Hi Ben,

Thanks for your answer and thanks for the Stl files!

I will try it myself.

I just used the 28byj motors because i want to build a cheap an simple machine for some kids workshops.

I watched different plotters and liked yours most, because of the inbuilt webserver and the possibility to use it without a Computer (unlike many other variations of wall plotters)

Let me know if you or somebody else is interested in my progress, then i will post about it.

Greetings Flo

If you’re interested, here the STL for the 28byj-48 holder I built when I was using them:

https://ben.akrin.com/downloads/28byj48_holder.stl
https://ben.akrin.com/downloads/28byj48_holder.jpg