OnStep Telescope Controller STM32 PCB Kits

A while back, I completed a port of the open source OnStep Telescope Controller firmware to the STM32 Blue Pill ARM Cortex M3 32-bit MCU. Later, Dave Schwartz and myself designed a Printed Circuit Board (PCB) that makes building a controller a far easier task than before.

Here is a video of the completed PCB.

And here is another video of my Vixen SXD, driven by the STM32 PCB.

You can directly order the parts yourself, detailed in the above links, from eBay or AliExpress. You can also order the PCB directly from JLCPCB, also from the link above.

Alternatively, Dave and myself offer the following kits, nearly at cost for those who want to convert their telescope to OnStep. We are not making any money from this, rather providing a service for fellow astronomers to promote the use of OnStep, and merely covering our costs.

There are the following types of kit available.

Kit A: PCB only

Cost: US $5
Availability: In stock.

Version 1.7

Ordering one or a few of this PCB is cheaper than ordering the minimum quantity (5) directly from JLCPCB, and also paying international shipping by courier (DHL).

You need to order the parts and modules separately from eBay or AliExpress. You have to wait for 6 to 8 weeks, and then put the kit together. Suitable for someone who has a workshop and has the parts already, or has access to a Make Space that would have the required bits and pieces.

Kit B: PCB plus 'Infrastructure' Parts

Cost: US $20
Availability: In stock.

By 'Infrastructure', we mean all the pin headers, female headers, power socket, resistors, capacitors, Molex KK connectors, etc. This is ready to solder to the PCB.

  • PCB
  • Pre-cut female headers (2 x 20-pin for STM32, 8 x 8-pin for drivers and WeMOS, 1 x 6-pin and 1 x 4-pin for RTC)
  • 2 x RJ-45 (8p8c for mount motors)
  • RJ-12 (6p6c for ST4)
  • RJ-9 (4p4c for focus motor)
  • 5-pin resistor network (ST4PULLUP)
  • 2-pin Molex, LED, LED holder, 470 ohm resistor (TRK-LED)
  • Right-angle SPDT switch, 3-pin Molex + extra 4-pin Molex shell (Flash-Run)
  • 2 x 3-pin jumper (J1, J2)
  • 5 x 2-pin jumper (J3, J4A, J4B, J4C, J4D)
  • 4 x 1-pin header for the LM2596
  • 3 x 100uf 50V electrolytic capacitors (C1, C2, C3)
  • Fuse holder (F1)
  • 5-pin Molex (MULTI)
  • 6-pin Molex (ST4PRT)
  • 6 x 4-pin Molex (pair for each stepper driver-to-connector cable)
  • Strip of 50 Molex contacts (6 more than required, for wastage or
  • Either an active buzzer, or a passive buzzer with 470 ohm resistor, depending on availability

This kit does not include the modules though, and you have to order them on your own and wait 6 to 8 weeks.

Kit C: PCB plus Parts and Modules

Cost: US $35
Availability: Out in stock, expected to be available in a few weeks.

This is a near complete kit. It contains everything in Kit B, plus all the required modules:

  • STM32 Blue Pill MCU
  • LM2596 power regulator
  • CP2102 micro USB module
  • WeMos D1 Mini WiFi

Note that these modules will be provided in their original anti-static packaging, as they are recived from China. That means that the pins are not soldered on, and we have not tested them.

Addon D: 3 X DRV8825 Stepper Drivers

Cost: US $9
Availability: 5 available.

These stepper drivers are low cost, and allow you to rapidly have a working controller. Their performance is definitely adequate for visual use, and some astrophotography (e.g. short focal length). Later you can decide to upgrade to the more expensive LV8729, if you wish.

Two are used for Axis1 and Axis2 motors, and the third one is for the focuser, if you want to use it.

Important Notes

By 'near complete', we mean that this kit still requires a case, and does not come with stepper drivers. There are two reasons for this: a) there are two options (maybe three in the future), and b), there is a wide price difference between the lowest-end option (DRV8825) and the highest-end (LV8729) so we can't stock the higher-end ones (because a pair of those is nearly worth as much as everything else combined).

At a minimum, you need to get 2 X LV8729 (recommended) or 2 X DRV8825 modules for axis1 (RA/Alt) and axis2 (Dec/Az). You may want to add an extra DRV8825 if you want to to motorize your focuser too.

Note that the somewhat more expensive LV8729 have better motor control and a support a lower MaxRate, and hence faster slewing speed than the really cheap DRV8825 (everything else being equal).

The kits require moderate soldering skills. There are no SMD components, so you don't need advanced soldering skills or equipment. Wire is not included (you are assumed to have access to a moderate amount locally). You will also need to have, or have access to, a Molex KK pin crimper. Your local Maker Space will have these, or that friend of yours who has all the tools ...

Motors or motor cables are not included, nor available: there are just too many variations for different mounts.

Project Box

A 3D printed box/case for the PCB is partially designed. This is based on the Universal Box from Thingiverse with a remix that allows holes in the panels. If you are willing to help and know OpenSCAD, please download the .scad file and start working on it, and let us know.

Assembly Instructions

Assembly instructions can be downloaded in PDF format from this link.

Shipping, Customs, Taxes and Duties

Shipping is extra, and will be quoted at near cost of packaging and shipping, from Canada.

We cannot use letters, since Canada Post restricts them to documents only.

We use the Canada Post 'Small Package, International Air' option, which typically takes 6 to 12 business days to arrive.

Judging from past orders, the cost is approximately US $9 to US $13 (at least for Kits A and B).

Any customs, duties or taxes charged by your government are also extra.

Please let us know which country you are located in (or the postal code if you are in Canada), and we will let you know how much shipping will be.


Payments are via Paypal outside Canada.

For Canadians, we take the loonie on par, and accept Interac e-Transfers.


We currently have only a limited amount of material to make up these kits, with a bit more on the way.

Since we don't know what the demand will be, we haven't invested in a lot of stock but will try to maintain a buffer and keep ordering more to satisfy projected demand.

This means that a kit may not be immediately available but will be satisfied, in priority order, as fast as we can get the parts from China (which is certainly as fast as you could get them unless you already live in China or Hong Kong).


You can order by filling this form.

PCB Change Log

We document here the changes that went from one version of the PCB to the other.

Version 1.07

- No circuitry changes.
- Flipped 6-pin ST4PRT Molex so pin1 is 5V (optional) and pin 2 is GND to match all ST4 implementations.
- Kits shipped with this version are HASL Lead Free.

Version 1.06

- No circuitry changes.
- Moved some components a little for extra clearance where needed.
- Improved the silkscreen layer for better visibility.
- Added car type fuse holder, in addition to glass fuse (one or the other is needed).

Version 1.05

- First orderable version.
- All test functionality verified to work.
- Kits shipped with this version used regular HASL (i.e. contains lead)

Version 1.00 to 1.04

Work in progress. Should not have been ordered nor used.