TOFU for Raspberry Pi Compute Module 4

In the latest issue of Custom PC magazine, Gareth Halfacree reviews Oratek’s TOFU, a carrier printed circuit board for Raspberry Pi Compute Module 4.

The launch of the Raspberry Pi Compute Module 4 family (reviewed in Issue 209) last year sparked an entirely unsurprising explosion of interest in designing carrier boards. This was aided in no small part by the Raspberry Pi Foundation’s decision to release its own in-house carrier board design under a permissive licence from which others could springboard with their own creations.

TOFU for Compute Module 4
Smartly designed with some clever features, the Tofu is a great carrier for a Raspberry Pi CM4 or compatible boards

Oratek doesn’t hide its inspiration. ‘Inspired by the official CM4IO board,’ chief executive Aurélien Essig openly admits, ‘it is intended for industrial applications. With user-friendly additions, it may also be used by enthusiasts looking for a compact yet complete solution to interface the many inputs and outputs of the single-board computer.’

The board is undeniably compact, although it bulks out when paired with the optional 3D-printed Switchblade Enclosure designed by Studio Raphaël Lutz. The reason for the name is that there are hinged lids on the top and bottom, which swing out for easy access, locking into place with small magnets when closed.

An optional adaptor converts the M.2 B-Key slot into an M-Key for NVMe storage
An optional adaptor converts the M.2 B-Key slot into an M-Key for NVMe storage

At least, that’s the theory. In practice, the magnets are a little weak; there’s also no way to fasten the lid shut beyond overtightening the screw in the corner. Otherwise, it’s a well-designed enclosure with top and bottom ventilation. Sadly, that’s not enough to prevent a Compute Module 4 from hitting its thermal throttle point under sustained heavy load, so you’ll need to budget for a third-party heatsink or fan accessory.

The Tofu board itself is well thought out, and finished in an attractive black. Two high-density connectors accept a Raspberry Pi Compute Module 4 board – or one of the increasing number of pin-compatible alternatives on the market, although you’ll need to provide your own mounting bolts.

TOFU for Compute Module 4 case
The 3D-printed case comes in an attractive ‘galaxy’ finish, but it isn’t cheap

The 90 x 90mm board then breaks out as many features of the computer-on-module as possible. The right side houses a Gigabit Ethernet port with Power-over-Ethernet (PoE) support if you add a Raspberry Pi PoE HAT or PoE+ HAT, two USB 2 Type-A ports, along with barrel-jack and 3.5mm terminal-block power inputs. These accept any input from 7.5V to 28V, which is brought out to an internal header for accessories that need more power than is available on the 40-pin general-purpose input/output (GPIO) port.

Meanwhile, the bottom has 22-pin connectors for Camera Serial Interface (CSI) and Display Serial Interface (DSI) peripherals, a full-sized HDMI port and an additional USB 2 port. These ports aren’t available outside the Switchblade Case by default, although a quick snap of the already-measured capped-off holes fixes that.

TOFU for Compute Module 4 case
Both the top and bottom rotate out of the way for easy access to the hardware inside

The left side includes a micro-SD slot for Compute Module 4 variants without on-board eMMC storage, plus a micro-SIM slot – hinting at another feature that becomes visible once the board is flipped. There’s also a USB Type-C port, which can be used for programming or as an On-The-Go (OTG) port. Oddly, there’s no cut-out at all for this in the Switchblade Case; if you want one, you’ll need to take a drill and file to it.

Turning over the board reveals the micro-SIM slot’s purpose. The Compute Module 4’s PCI-E lane is brought out to an M.2 B-Key slot, providing a connection for additional hardware including 3G/4G modems. For storage, you can use an optional adaptor board to convert it to M-Key for Non-Volatile Memory Express (NVMe) devices, with a spacer fitted for 2230, 2242, 2260, or 2280 form factor drives.

TOFU for Compute Module 4 ports
The Tofu has plenty of ports, but no USB 3

That’s not as flexible as it sounds, unfortunately. The spacer is soldered in place and needs to be chosen at the time of ordering. If you want to switch to a different-sized drive, you’ll need another adaptor.

There’s one other design point that makes the Tofu stand out: the inclusion of a user-replaceable fuse, a Littelfuse Nano 2 3.5A unit that was originally designed for automotive projects. 

While it’s primarily there for protection, it also enables you to cut off the on-board power supply when the board is driven through PoE. With the fuse in place, there’s clearly audible coil whine, which can be silenced by carefully popping the fuse out of its holder. Just remember to put it back in if you stop using PoE.

The biggest problem is price. At 99 CHF (around £78 ex VAT) you’ll be into triple figures by the time you’ve picked up a suitable power supply and Compute Module 4 board. The M.2 M-Key adaptor adds a further 19 CHF (around £15 ex VAT), and the Switchblade Case is another 35 CHF (around £28 ex VAT). If you have access to a 3D printer, you can opt to print the latter yourself, but you’ll still pay 8 CHF (around £6 ex VAT) for access to the files.

The Tofu is available to order now from oratek.com. Compatible Raspberry Pi Compute Module 4 boards can be found at the usual stockists.

Custom PC issue 217 out NOW!

You can read more features like this one in Custom PC issue 217, available directly from Raspberry Pi Press — we deliver worldwide.

custom pc front cover

And if you’d like a handy digital version of the magazine, you can also download issue 217 for free in PDF format.

7 comments
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At one point, I’m going to spice up my CAD knowledge and will create a board like this so that it fits into my Asus EEE-PC 901.

Reply to Misel

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I was thinking about one for my eee-pc1001

Reply to Per-Oskar Odermalm

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This, but OLPC laptop and give it to the nephew. I hate that I’ve never really used it in 10+ years.

Reply to smorrow

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There’s been some really great concept boards come out for the CM4. It’s a real shame we’ve got the current global chip shortage as it looks like a fair few are struggling to get their boards built right now.

I’d kill for a mini-itx compatible board with either a bunch of m.2 sockets or a couple of pci-e slots for expansion. A standardised format like that would allow for some awesome projects to be built.

It’d take the pi truely into the Desktop Computer territory, with the ability to have expansion cards.

Reply to Rick

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There are at least three Mini-ITX or Micro-ATX board designs I’ve been following, and sadly all of them have been slowed down significantly by the shortage.

Nobody can do things with the volume to get deals on necessary chips, so each design I’ve followed has had to compromise somewhere and drop some features just to get prototypes built—and most of them are still trying to get to a first working design because of all that rework!

There are a few carriers that are very useful though, and some groups like Waveshare have been pumping out a lot of different designs that can be mounted in a variety of places. Still waiting on an ATX/ITX board though!

Reply to Jeff Geerling

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Hi Jeff
I love your show and follow it religiously!
You are correct in saying that the there are very promising designs out there that incorporate the CM4, I’ve been following the Turing Pi 2 project closely. The chip shortage has been a massive bummer across all industries and it is such a pity that great Idea’s are being docked until the shortage lets up, one can only hope that the projects resume once supply becomes stable again.

Keep up the great work!

Reply to Dwain Van Der Westhuizen

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+1 on the Geerling worship

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