A new parallel project - PicoBETH-J

[206cc]

PicoBETH has just reached its three-year mark, and over that time I have accumulated a lot of real-world experience, test results, and feedback from users in different places. Along the way, I also started thinking about what the same basic idea might look like if it were developed in a different direction.

That is where PicoBETH-J comes from.

PicoBETH-J is not intended to replace the original PicoBETH. The original project will continue to keep its flexible and DIY-friendly approach, while PicoBETH-J will explore a more standardized and integrated hardware design.

Instead of changing the direction of PicoBETH itself, PicoBETH-J gives me another space to rethink the structure, PCBs, wiring, mounting, maintenance, and software as one complete system.

PicoBETH-J is still in the planning and design stage. Since I also have a full-time job, I am not trying to rush the development, so this may remain a long-term side project.

The development process will also be a little different this time. With PicoBETH, I often released changes as soon as something new was ready so everyone could test them together. For PicoBETH-J, I plan to wait until the main design, testing, and documentation are reasonably complete before releasing the project as a whole.

I have also created a separate Instagram account, @picobeth_, to keep a record of the PicoBETH-J development process. Besides design, building, and testing updates, I will also share some badminton, racket stringing, and DIY-related content there.

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The core idea behind PicoBETH-J

PicoBETH-J will keep the same three core ideas as PicoBETH:

Economical・Intuitive・Accurate

The difference is mainly in how the hardware will be approached.

While the original PicoBETH keeps more flexibility for different DIY setups, PicoBETH-J will explore a more standardized hardware configuration.

Some of the parts currently planned include:

• SGX1610 linear stage
• DM542C stepper motor driver
• Pololu D24V22F5 5V power module
• NJ5 50kg load cell instead of the 20kg version mainly used before

These are only some of the parts that have already been decided or are currently being considered. More components may also become standardized as the design develops.

By limiting some hardware choices, PicoBETH-J should be able to reduce the uncertainty caused by different component combinations and make different builds more consistent in performance and stability.

Maintenance will continue to follow the same approach as the original PicoBETH, keeping parts easy to remove and replace. Most components can still be replaced in just one or two disassembly steps.

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Main areas currently being explored

1. Main structure and exterior

The overall structure will combine ideas from the HW2 version and the 3D-printed design.

I plan to keep only the minimum amount of aluminum needed for the main load-bearing structure, currently:

• L-shaped aluminum angle
• Aluminum square tube

Most of the other exterior and functional parts will be redesigned for 3D printing, with a better balance between function, maintenance, and appearance.

A new 3D-printed Drive Box will also be added to house the DM542C, power distribution board, and related wiring.

The goal is to reduce exposed electronics and loose wiring, giving the overall build a cleaner and more integrated appearance.

The dust cover will also be redesigned, including better protection for the linear rail.

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2. Fabrication

I’ll also design a set of 3D-printed machining jigs, mainly for the small number of aluminum structural parts used in PicoBETH-J.

The jigs will be used for things such as:

• Cutting or machining aluminum parts to the correct size
• Screw-hole positioning
• Drilling alignment
• Improving consistency between repeated builds

The goal is to reduce the time and difficulty of working with the aluminum parts while improving accuracy.

Even though PicoBETH-J will still use a small amount of aluminum for the main load-bearing structure, I hope the jigs can make this part of the build much easier. DIY builders should be able to make consistent parts without needing much large-scale machining equipment.

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3. PCB

The existing Main PCB and Button PCB concepts will be redesigned specifically for PicoBETH-J, and a new Power Distribution Board will be added for power distribution and protection inside the Drive Box.

Main PCB

The GPIO assignments will be rearranged mainly to improve PCB routing and layout.

The button inputs will also change from using the Pico’s internal pull-down resistors to external pull-up resistors.

The Main PCB and Button PCB will be connected with a single 12-pin ribbon cable, reducing the number of cables and connectors between the two boards.

Button PCB

The buttons will use standard Cherry MX switches, commonly found in mechanical keyboards.

LED backlighting will also be added, together with standard keycaps, making the buttons easy to replace while improving feel and durability.

Power Distribution Board

The Power Distribution Board will handle power distribution and protection inside the Drive Box.

The main power and device connections will use proper connectors instead of twisted-wire connections, making the wiring cleaner and more reliable.

It will also include:

• Reverse-polarity protection
• Fuse protection
• Centralized power distribution

All three PCBs will also have dedicated 3D-printed mounting parts, so the boards, wiring, and enclosure all have fixed mounting positions instead of needing improvised mounting methods.

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4. main.py

Because PicoBETH-J will use different GPIO assignments and external pull-up resistors for the buttons, its main program will not be directly compatible with the original PicoBETH hardware.

The user interface will probably stay fairly close to the current PicoBETH design, so the general way of using the machine should remain familiar.

The internal code will also be reorganized, and I plan to test PWM-based motor pulse control to see whether it can further improve motor control.

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5. Other ideas

There are also a few other ideas I am currently considering.

One is adding a USB Type-C fast-charging output to the Drive Box.

Besides charging a phone or other device, it can also provide 9V / 12V / 19V output for other accessories.

For example, the grommet flaring tool I use runs on 12V, so it could be powered directly from the Drive Box. That means one less power adapter on the table and simpler wiring around the stringing machine.

I also plan to test a higher-torque stepper motor and see whether the SGX1610 linear stage can reliably reach around 80 lb of usable pulling force.

This is still only a test direction for now. Whether it will actually be suitable for regular use will depend on later pulling-force, stability, and durability tests.

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Everything above is still part of the current plan, so many details may continue to change after actual building and testing.

PicoBETH and PicoBETH-J will follow two slightly different paths.

PicoBETH will continue to keep its flexible and open DIY approach, while PicoBETH-J will explore a more standardized and integrated way of building around the same core idea.

Neither one is meant to replace the other. PicoBETH-J is simply another direction I wanted to explore after working on PicoBETH for three years.

If you have any ideas or suggestions for PicoBETH-J, feel free to share them here.

If you would like to follow the project, you can also find it on Instagram at @picobeth_. Future PicoBETH-J development updates and build logs will mainly be posted there, along with some badminton, racket stringing, and DIY content.

[herbyderby]

Exciting! I'm happy with the part choices so far (my machine uses all of them already). Do you think it will be feasible to do the metalworking with only hand tools? I don't have a drill press, for example.

Some minor suggestions beyond what you have listed:

• It would be nice to reduce the overall footprint, mainly the length. It sticks out a fair bit beyond the end of my machine.
• Some of the parts are harder to source than others, which would be nice to take into account. For example, I could not find a "high level active buzzer module" locally. The buzzer component itself is easy to find--perhaps it could be integrated into the PCB directly?
• I like the idea of simplifying the cabling. On that note, creating JST cables manually is pretty annoying. I did buy a crimper and use it a little, but eventually just bought pre-crimped cables.
• Regarding the SGX1610, for tennis it is increasingly rare for people to use high tensions. The trend is going lower and lower. It is hard for me to imagine needing to support beyond 65lb or so, FWIW.

[206cc]

Thanks a lot for the suggestions!

1. I have thought about shortening the linear stage. I’m currently using the 200 mm version. There is a 150 mm version available, but it seems quite difficult to source. The 100 mm version may be a little too short for badminton, but I think I can try changing the positions of the front and rear limit switches and see if the full 100 mm travel can be utilized more efficiently. I’ll add this to the list of things to test in the future.

2. The buzzer suggestion is very good. Besides integrating the buzzer directly onto the Main PCB, I think it may even be possible to add adjustable buzzer volume.

3. I’m actually not very familiar with tennis. If most users stay below 65 lb, then there may not be much need to strengthen the design further. The SGX linear stage will also have a shorter service life when used continuously at such high tension.

Thanks again for your suggestions. They are very helpful.

[CarlosOnline]

Is it possible to completely remove the LCD panel and button interface and replace it with my phone or iPad using the Wi-Fi for communication?

I briefly looked at implementing this but found that the raspberry Pico only supports two threads which wasn't enough to run a UI as well.

Any chance the Pico could be replaced by a hopefully not too expensive processor that can run more than two threads?

[206cc]

I think this is a very interesting idea, and technically it should be possible. A simple web-based UI over Wi-Fi could probably be implemented even with the Pico W.

For PicoBETH, though, my core idea has always been to keep the machine simple, independent, and easy to operate without relying on another device, so this direction is a little different from what I originally had in mind.

But I think it would be a very interesting direction to explore, and if you’re interested, it could even become a separate GitHub project based on PicoBETH.

[CarlosOnline]

Yes I am interested. My initial attempt was with the Pico w. However I found the web server was unresponsive due to the software always pulling and responding to the hardware.

Switching to an interrupt implementation should provide more cycles to run a web server.

The c++ version that a user mentioned may also help as it seems to be more efficient / faster.

Please let me know how you would like to proceed. Thank you.

[jqzhouuh-cloud]

"I suggest switching to a closed-loop stepper motor module for more precise motor control. This would eliminate the need for the Pico to monitor and process the limit switches. Furthermore, the current combination of the DM542C and Pico significantly limits motor speed; if the pulse interval is reduced too much, it leads to missed steps.

Additionally, could the string clamp mechanism be structurally optimized to automatically trigger upon clamping? This would avoid the need for the advanced microswitch setup used in the current Pico project."

[206cc]

Yes, both ideas are definitely possible, and similar approaches have actually been suggested before.

I’m always happy to see people who are interested in the project experiment with and develop these kinds of improvements. My original goal with PicoBETH is to provide a simple, reliable, and low-cost base system that is easy for people in different countries to build.

Because of that, when I choose parts, I have to consider not only performance, but also price, availability, ease of assembly, and how easy the parts are to replace.

If you successfully test these modifications, I’d really encourage you to share the hardware, wiring, code, and your experience in the Discussion. I think many users would be interested in these kinds of advanced upgrades.