This little device has one of the most unique and hard-to-find computers on the planet inside.
It's called the RevPi Connect S, and a company called Revolution Pi sent it to me to test.
Revolution Pi's been making industrial Pi computers since 2016, and they have this entire
lineup of 'Connect' modules, with expansion packs like the DIO box they also sent, that
adds 14 digital inputs and outputs.
Their whole lineup was based on the Raspberry Pi Compute Module, this thing.
But for the past year or so, it's been impossible to get these older Compute Modules.
When Raspberry Pi upgraded to the Compute Module 4, they also used a new form factor
with connectors on the back instead of the edge.
But that meant older devices like the RevPi Connect couldn't use 'em.
So instead of letting these older designs just die off, Raspberry Pi teamed up with
companies like Revolution Pi and made this—the funky little Raspberry Pi Compute Module 4S.
I call this 'the resurrected Pi', because the board says 2020 on it.
That means they were probably working on it around the same time as the Compute Module
4, but decided not to put it into production.
Raspberry Pi wanted to add features like built-in Gigabit Ethernet and PCI Express, so they
were forced to change the form factor for the newest Compute Module.
The new design won out, and they shelved the Compute Module 4S.
That is, until the PC component parts shortage hit in 2020 and it was basically impossible
for Raspberry Pi to make any more old CPUs.
So they resurrected the design and there's at least one batch of these old-style CM4S
modules, but they're only available through resellers like Revolution Pi.
There's even a listing for it on the Pi Website, but there's no way to buy it.
I mean, right now it's kinda impossible to buy any Raspberry Pi, but there's not even
a Buy link on the page to get your hopes up.
And that's probably intentional.
I put this thing through its paces in three different carrier boards, and because of the
old form factor, you miss out on a lot of power from the more modern BCM2711 chip.
First of all, you only get 100 Megabit networking.
The RevPi Connect gives you two ports, which is nice, but it's still stuck at 100 Megabits
per port, using these little SMSC LAN chips.
The RAM and CPU are both faster like all Pi 4 models, but the CPU seems to maybe be hampered
a bit, and I'm not sure why.
It showed up as a 4-core CPU with a 1.5 Ghz clock, just like on the Compute Module 4.
But when I ran benchmarks, single core scores were usually very close, but multicore tests
were a lot slower.
There could be some other factors there, like a realtime patch that was running on the module
I benchmarked, but I also tried with a fresh Pi OS install, and it was still slower on
multicore.
Oh, and you might be wondering why this thing is delidded.
There's not the normal 'heat spreader' or 'IHS' that you see on most Pi CPUs.
Well... let's just say I 'accidentally' delidded it.
The RevPi is a fanless enclosure, so Revolution Pi decided to use thermal epoxy—not just
thermal compound—to make sure a large heat sink would stay on top of the Pi to keep it
cool, and wouldn't fall off, even in a high-vibration industrial environment.
Well... that's great for the RevPi Connect, but the heatsink stuck out too far for other
boards I wanted to test, like this Compute Module 3 PoE board.
I was originally trying to get it to run by just setting this IoT plug on it to make sure
all the pins made contact, and that worked, but it was less than ideal.
So I tried the trick of freezing the heat sink with some compressed air turned upside-down,
and then quickly tapped the heatsink with a hammer.
But apparently the thermal epoxy Revolution Pi put on is stronger than the thermal glue
on the heat spreader, and, well, now I have maybe the world's first delidded Compute Module
4S.
I stuck this other heatsink directly on the CPU die and kept testing.
It only got a few degrees hotter, but it didn't seem to affect the scores.
I also tried the CM4S on the Turing Pi cluster board, and it booted and worked.
I could get HDMI and USB, but it didn't seem to connect to my network through the onboard
Ethernet switch, but I'm not 100 percent sure why.
So it does look like the CM4S is pretty much a drop-in replacement for older Compute Modules,
with some caveats.
Getting back to the RevPi Connect S, though, it's a solid DIN-rail-mount industrial computer.
It's UL listed and has a bunch of certifications, it has a modular expansion system, like with
this DIO they sent me, and they have a lotta software support so you can get it up and
running quickly.
The whole enclosure snaps together, but it's molded very well with high quality plastics,
and so far its survived about 8 teardowns through all my testing.
I think it's also nice they added a few extra helpful bits, like this exposed micro HDMI
port for easy debugging.
A lot of industrial Pi hardware neglects helpful features like that.
Overall this is a great little package, and as one of the oldest Industrial Pi manufacturers,
Revolution Pi sets a pretty high bar for quality and support.
They're working on a proper Compute Module 4 version of the RevPi Connect series, and
it'll be exciting to see what they do with gigabit Ethernet and PCI expansion.
The biggest downside is the price.
It's around 400 bucks with a Pi with 1 gig of ram and 8 gigs of eMMC storage.
Expansion modules are anywhere from 100 to 300 bucks.
But that's par for the course with industrial Pis.
I talked more about that in my video about why Industrial Pis are so expensive, so go
check that video if you want more.
Until next time, I'm Jeff Geerling!