The smallest open source switch – how it works, what it can offer, opinions and some alternatives
Students at a school in New Hampshire have designed a 5-port network switch they've dubbed “the world's smallest.” They transferred their developments to open source. Let's briefly look at the component base of the switch, discuss the opinions of the community, and also take a look at some similar projects.
What is this device
The device is called mrxSwitch and is suitable for use in consumer electronics and robotics. Actually, the need to design such a device became a prerequisite for the development of this switch. Its authors are students Phillips Academy Exeter. This is a private school that uses Harkness technique and has large library. The MUREX Robotics team took part in underwater robotics competitions and made their own robot capable of performing tasks in the pool. They needed a compact switch to connect a custom CM4-based board, PLC-module and several IP cameras for a computer vision system. However, existing solutions were either too cumbersome or too expensive. Then the students decided to design their own device, and then posted diagram and documentation in open access.
The basis of the device put IP175G integrated circuit because it is reliable, affordable and easy to use. Although young engineers noted that it can be replaced with RTL8305NB-CG or IP175GHI (if the ability to operate in a wider temperature range is required). In any case, the choice of IP175G was not without difficulties: in particular, datasheet It was difficult to read due to typos.
As for the base components, initially MUREX Robotics chose QT24A23 and BT16A07 transformers. But the latter was not available in the store, so it had to be replaced with HY601680. They also used a linear voltage regulator LM1117 with an output voltage of 3.3 V and a maximum input voltage of 15 V. As connectors used Molex PicoBlade. At the same time, the developers turned to termination using the Robert Smith Termination method, which helps reduce the influence of common-mode noise. According to the authors of mrxSwitch, their chosen method is also approved by engineers from the Japanese manufacturer of semiconductor components Renesas.
The first version of the switch was released in 2023, and even then MUREX Robotics noted several points that could be improved. So, one of them was related to the size of the board (they considered it too big). But since then, engineers have improved the design of the switch and made several changes to it. In particular, reduced mrxSwitch size by 30% – to 44.9 x 42.2 mm – which, according to the authors, makes the switch the smallest in the world (at least as of June 2024). They also replaced both microcircuits QT24A23 on QT48A03 — that is, they chose a cheaper and more compact solution. In the future, the engineering team plans to continue improving their product.
What the community is saying
The tool attracted the attention of Hacker News residents, and a discussion ensued in the thematic thread. Overall, the community has been positive about the new hardware. Some noted that such a compact switch will find application in robotics, which is not surprising given the circumstances that led to its development. One of the site users also suggested that mrxSwitch will be useful in amateur avionics. He said that such a device would be useful for his team when rocket development for competition FAR-Mars, in which students had to develop a rocket using liquid oxygen or liquid methane, capable of rising to an altitude of up to 15 km. The Hacker News resident was part of a team from Purdue University, and they were using an $80 ethernet switch. He says an open source project like mrxSwitch would allow his team to save money.
But, of course, it was not without a bit of criticism. User HN suggested that the device could get very hot due to its design. He noticed that linear voltage regulators operate in such a way that they dissipate residual power as heat. And one of the developers mrxSwitch confirmed, that the switch actually heats up to 60°C, so I recommended using a radiator. They are thinking add it yourself, or implement a high-frequency DC-DC converter. Editors of the specialized online publication Tom's Hardware, also notedthat a speed of 100 Mbit/s may seem quite low by modern standards, but it is fully justified by the cost of the equipment.
What analogues exist
Of course, mrxSwitch is not the only compact switch (although the authors claim that it is the smallest in the world). An alternative could be the device SwitchBlox, the dimensions of which are 44.5 x 44.5 mm. The switch has five 10/100 Ethernet ports and is suitable for use in unmanned aerial vehicles and other autonomous systems. SwitchBlox price amounts to about $70, but the sources can be found on GitHub (but only Kicad files for now).
Among the alternative products you can also highlight industrial switch PE-505 from BrainBoxes. Its dimensions do not exceed 55 x 55 mm and it can operate at temperatures from -40 °C to +85 °C. The device operates at 10/100 Ethernet speeds and complies with the IEEE 802.3az standard. If you want to take a closer look at the specifications of this switch, here it is datasheet.
Interestingly, the constant reduction in network and other devices creates new challenges for engineers. One of them is related to the need to proportionally reduce the connectors while maintaining connection reliability. The laws of physics are difficult to cheat, so the only way to reduce the size of the connector is to place the contacts closer together. But connectors whose pin spacing is less than 0.35 mm may require special approach in production.
Therefore, some seek to circumvent this limitation. Thus, Molex last year introduced a family of high-density inter-board connectors. The connectors were divided into pairs and placed “ladder”. This method of pin arrangement made it possible to reduce the connector length by 30% compared to other board-to-board connectors.
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