# gSender on Pi 3B+ **URL:** \ **Category:** ❓ Question\ **Created:** [August 9, 2026, 1:39pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875 "2026-08-09T13:39:29Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 9, 2026, 1:39pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/1 "2026-08-09T13:39:29Z")
Hi, new (potential) user here wanting to upgrade from Mach3. After 14 years using that venerable and unsupported CNC application on Windows machines I am finally thinking about an upgrade to my mill. At the moment I have a Windows NUC with USB to a UC100 to a BoB, thinking of replacing the BoB with a suitable board running grblHAL. One nice option would be to replace the NUC with a Pi 3B+ of which I have two spares. As far as I can see the latest version for the RPi is 1.6.1 which I have downloaded on a Pi500 desktop and it seems at least to load and open fine. Two questions if I may (and I didn’t find clear answers on the megathread). 1. Will the latest RPi image run on the 3B (assuming its OS is upgraded to 64-bit)? 2. A side issue - any recommendations for a processor board to run grblHAL? Many thanks in advance, John. ---
**Author:** ![KGN](https://forum.sienci.com/letter_avatar_proxy/v4/letter/k/c77e96/32.png) [@KGN](https://forum.sienci.com/u/KGN)\ **Post date:** [August 10, 2026, 3:33pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/2 "2026-08-10T15:33:41Z")
It should be fine given 64 bit, performance might depend on specs. I’ll not answer the controller board question, since I work for the company and obviously am going to recommend our own products. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 10, 2026, 4:02pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/3 "2026-08-10T16:02:16Z")
Thanks Kevin! I understand your reservations on the recommendation! ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 10, 2026, 5:03pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/4 "2026-08-10T17:03:07Z")
@JohnHaine Since I don’t work for “the company” as @KGN does, I do not have any reservations about suggesting that you look at the SLB from Sienci. I switched from the original LM controller as soon as the SLB became available and it has been solid from day one. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 10, 2026, 9:40pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/5 "2026-08-10T21:40:24Z")
Thanks for that. It does look a good solution, but as I understand it (though the description isn’t absolutely clear) it includes integral stepper drivers. I already have a chassis with 4 quite reasonable drivers and a PSU, all I really need is a motion controller to replace the UC100/BoB so I rather favour using an OTS processor card running grblHAL - I can sort out the interfacing etc myself. ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 10, 2026, 11:00pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/6 "2026-08-10T23:00:48Z")
@JohnHaine Understood. Just to keep promoting 😀, maybe the SLB-EXT would be a better fit. It does not have the drive motors on the board. ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [August 10, 2026, 11:33pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/7 "2026-08-10T23:33:47Z")
The way I read this thread, the OP has open loop stepper motors. Is the output of the SLB-EXT suitable for open loop steppers as long as external drivers are used? ---
**Author:** ![gwilki](https://forum.sienci.com/user_avatar/forum.sienci.com/gwilki/32/366_2.png) [@gwilki](https://forum.sienci.com/u/gwilki)\ **Post date:** [August 10, 2026, 11:41pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/8 "2026-08-10T23:41:42Z")
@Jens Good question. I don’t see anything in @JohnHaine posts that describe the steppers as open loop or closed loop. I don’t know if the SLB-EXT can be used to control open loop steppers, either. You could write books about what I don’t know. 😀 ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [August 10, 2026, 11:54pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/9 "2026-08-10T23:54:05Z")
OK, I made some assumptions based on ‘Mach3’ and ‘BoB’ which I associate with open loop motors. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 11, 2026, 7:57am UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/10 "2026-08-11T07:57:21Z")
Correct, I have open loop steppers. They also run from a 36v supply. I’m confused about the SLB-EXT, the description is ambiguous. The -EXT suffix might indicate it uses external drives but then it needs a 48V 10A supply! Not having a clear specification is putting me off a bit! ---
**Author:** ![DavidB](https://forum.sienci.com/letter_avatar_proxy/v4/letter/d/76d3ee/32.png) [@DavidB](https://forum.sienci.com/u/DavidB)\ **Post date:** [August 11, 2026, 1:09pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/11 "2026-08-11T13:09:17Z")
The[FAQs](https://sienci.com/product/slb-ext-closed-loop-controller/)section for the SLB-EXT states it only works with closed-loop Nema 23s. It requires the 48V 10A supply because if you get an AltMill all the data and power for the motors are connected directly to the SLB-EXT with single set of cables. This makes it cleaner/easier. You do not need to use the 48V power supply provided on the SLB-EXT and can use some external power source for motors and only need the data lines for the motors. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 11, 2026, 6:06pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/12 "2026-08-11T18:06:51Z")
OK, thanks for that clarification. But I understand that it doesn’t have the actual stepper drivers on board, just outputs step and direction pulses, so what makes it only work with closed loop motors? ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [August 11, 2026, 10:41pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/13 "2026-08-11T22:41:01Z")
Keeping in mind that the following is just a WAG: The device that makes it go, the driver, is hanging off the back end of the motor. I assume that the output of the SLB-EXT is power (presumably DC straight from the power supply) and the four individual phase signals (probably straight TTL output). A position decoder is part of the driver. The part that I don’t quite understand is how the SLB-EXT gets notified of a motor fault. Edit: Looking at the ‘data’ connector from the SLB-EXT to the individual motors, there are eight conductors so there is obviously more than just step and direction involved. I did not look at the detailed schematics. Yet another edit: More details are here: [Closed Loop Stepper Motors - AltMill CNC](https://resources.sienci.com/view/am-closed-loop-stepper-motors/) and the signals are step, direction, enable and alarm (+ and - in all cases) ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 13, 2026, 8:52am UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/14 "2026-08-13T08:52:12Z")
Jens, that’s great, thanks. So if using standard open-loop drivers one can hardwire the SLB-EXT alarm input to the appropriate logic level for “not alarmed”. All clear now. ---
**Author:** ![Jens](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/d2c977/32.png) [@Jens](https://forum.sienci.com/u/Jens)\ **Post date:** [August 13, 2026, 1:18pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/15 "2026-08-13T13:18:22Z")
That is not what I said. While you can of course try this, you are totally on your own. I would suggest that you confirm everything with Sienci before deciding on which controller you order. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 13, 2026, 1:51pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/16 "2026-08-13T13:51:51Z")
I’m reading between the lines as they seem to promote the EXT for updating existing machines. But considering the EXT costs more that the standard yet seems not to have built-in drivers it doesn’t look a great solution for me. What I need is a low cost way to try out gSender on my existing machine. Anyway thanks for the useful inputs. ---
**Author:** ![marcoose](https://forum.sienci.com/letter_avatar_proxy/v4/letter/m/7ea924/32.png) [@marcoose](https://forum.sienci.com/u/marcoose)\ **Post date:** [August 14, 2026, 12:22pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/17 "2026-08-14T12:22:03Z")
If you just need something to go from USB serial to step/dir signals, I would look at the grblhal supported boards: > **[GitHub - grblHAL/Controllers: List of controllers supported by grblHAL](https://github.com/grblHAL/Controllers)** > > List of controllers supported by grblHAL there’s a bunch of 3D printer boards that should do the trick. Many have ‘sockets’ for typical little stepper drivers, but also have separate step/dir headers. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 14, 2026, 1:57pm UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/18 "2026-08-14T13:57:17Z")
Thanks - that’s what I’m tending to. One of them is the USB interface available for Mach3 with a “white eagle” logo, these are very cheap and have opto isolated I/O. Should be a pretty well drop–in replacement for my BoB. ---
**Author:** ![JohnHaine](https://forum.sienci.com/letter_avatar_proxy/v4/letter/j/779978/32.png) [@JohnHaine](https://forum.sienci.com/u/JohnHaine)\ **Post date:** [August 16, 2026, 9:05am UTC](https://forum.sienci.com/t/gsender-on-pi-3b/26875/19 "2026-08-16T09:05:04Z")
Just to conclude, I ended up ordering a picoBOB from Expatria - looks like it should plug in directly to my existing BoB in place of the UC100. Also I like the RPi pico, and most of the current "white eagle boards seem to be missing the programming port. Thanks for the useful input.