Embedded Project Video

This is an HP N40L MicroServer. After nearly 15 years its original processor, USB 2.0 connectivity and ageing hardware are becoming increasingly limiting.

So rather than replace the server, I decided to replace the motherboard.

I started with the Raspberry Pi Compute Module 5 IO Board reference design and turned it into a completely custom motherboard designed

specifically around the HP N40L chassis.

PCBWay sponsored the manufacturing for this project by providing the PCB, assembly and X-ray inspection. Many thanks to PCBWay for helping make the physical board possible.

A Mini-ITX conversion was something I considered, but the N40L does not use entirely standard mounting locations or a conventional removable rear I/O shield. Fitting a normal motherboard would therefore require modifications to the case, potentially including cutting the rear panel and making a custom I/O shield.

I wanted the machine to remain as close to completely stock as possible.

The resulting board fits the original motherboard location and adds:

• Raspberry Pi Compute Module 5

• Gigabit Ethernet

• USB 3.0

• HDMI

• NVMe storage

• Continued use of the original power supply

• Continued use of the original chassis and drive bays

The original four drive bays haven't been populated in my current build yet, but they haven't been abandoned. The N40L uses an SFF-8087 Mini-SAS connection for the drive cage, and this can be connected using a suitable M.2/PCIe to SATA expansion controller. I have already proved the storage interface works, so adding the original bays later does not require modifying the chassis.

Most of the project was therefore not simply adapting an existing board. I had to work through the schematic, component selection, mechanical measurements, connector placement, power supplies and high-speed PCB routing while making everything fit a chassis designed around completely different hardware.

This was also the first complete motherboard I have designed.

Somehow, it worked on the first attempt.

I documented the complete process in my YouTube video, from measuring the original machine and designing the PCB through to manufacturing, assembly and finally powering it up:

https://youtu.be/AzW4rRsD8Uk

This ShareProject page is intended as a showcase of the engineering project rather than a ready-to-build product. This board is a one-off prototype designed and tested for my own N40L, so I am not publishing the Gerbers, BOM or manufacturing files.

If I were to develop a second revision, there are already several things I would change.

I would aim to reduce the cost and board area, improve the integration with the original front I/O, and generally refine the design with reproducibility in mind. The current board proved the concept and achieved what I wanted from the project, but I would not want to present this revision as a finished design for others to manufacture.