Choosing Electronics for Onstep with a 12″ Dobsonian

I’m documenting my complete process of learning while I try to convert a 12″ Zhumell Z12 Dobsonian to GoTo using Onstep. The Onstep Wiki and Message Board contain a wealth of information, but much of it is written by people who are MUCH more comfortable with electronics than I am. They are so good at what they do, they forgot the simple questions that a total newbie will have. I am going to document my build in as much detail as possible to hopefully empower other newbies like myself to take the plunge.

After reading the Wiki, I decided the easiest starting point for myself was to go with the WeMos R32 with CNC V3 Shield. I’m going to keep my first build as simple as possible while I learn. I may choose to upgrade features in the future. This initial documentation will focus on getting a WeMos R32 up and running with a CNC V3 Shield, and appropriate stepper motors and drivers.

UPDATE: This ended up being harder than expected with the TMC2130 drivers. Take the advice from the OnStep Wiki and just use a fixed microstep driver like the LV8729. After having issues with the CNCV3 Shield and TMC2130 drivers, I opted to try out the OnStep Shield by Roman Hujer. I found this at, but you don’t have to buy from there. George Cushing assembles full kits, which is the closest thing to a complete kit I have found. I’m going to document my experience with the OnStep Shield in another post to keep this one as clear as possible.

Here’s the TLDR version of my components used, with approximate prices (2022). There are many places to buy these such as Amazon, eBay, Ali Express… Amazon isn’t always the cheapest, but it had available parts when I was ready to order, which is rare in 2022.
CNC Shield V3 – $11
UNO R3 D1 R32 ESP32 – $11
TMC2130 V3.0 Drivers, 4 pack (only need 2) – $33
Random Wiring I ordered to help assemble – $7
Jumpers / Headers – for setting microstep mode and SPI – $9

First things first: I didn’t know what a WeMos R32 was. It’s an Arduino Compatible board, but not made by Arduino. The WeMos R32 uses the ESP32 processor, and takes all of the programming that an Arduino does. This WeMos R32 board is the ‘brains’ of the setup. It holds software and sends commands to the motor drivers.

The motors I chose are a set of 400 step Nema 17, 0.9 Amp stepper motors. As of this writing, I actually don’t know if these will work, but since I’ll be gearing these down around 300x to 500x, I think they’ll have enough torque for this scope.

I chose the TMC2130 SPI drivers. I chose these because they were available on Amazon, while many other driver options were not available in the U.S., at least not for many months. They can handle up to 1.2A RMS, so they should be fine to use with 0.9A motors. Drivers take the signals for step and direction from the WeMos, take additional power from a power supply, and amplify that to send it to the motor coils.

The final electrical piece used is an Arduino Shield Called the CNC V3 Shield. What is an Arduino “Shield” in general? My simplistic answer is: A shield is any board that plugs on top of the standard Arduino. Think of it as template wiring that makes it easier to connect other electronics to the Arduino so you don’t have to run as many wires and solder your own components together. The CNC V3 Shield makes it easy to plug in stepper motor drivers to the Arduino. It’s not technically needed, but it looks to be a real time saver, and for around $10 it’s worth it.

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