Raspberry Pi 400: The inside story of how the $70 Pi-powered PC was made

The four-year journey to take the Raspberry Pi 4 from a sketch to a full product.
Written by Liam Tung, Contributing Writer

The new $70 Raspberry Pi 400 computer made what seems like a well-timed debut; a budget personal computer that arrived at the right time to help keep people online during the pandemic.

But the device – a complete PC built into a sleek red and white keyboard – was actually four years in the making.

The compact design is one that explicitly harks back to the classic home computers of yesteryear, like the BBC Micro, ZX Spectrum and Commodore Amiga, which integrated the motherboard directly into the keyboard. Indeed the ZX Spectrum and BBC Micro, were both conceived in Cambridge, England, which is also where Raspberry Pi Trading has its headquarters.

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But while the look of the Raspberry Pi 400 might be a reminder of the past, the components are far more up to date; a Raspberry Pi 4 computer with 4GB of RAM encased in a keyboard with ports to connect a mouse, display, power, add-ons, and Ethernet, plus dual-band Wi-Fi and Bluetooth. It's also about 40 times more powerful that the original Raspberry Pi, and the company says that level of power offers an experience that is indistinguishable from a legacy PC "for the majority of users".

Simon Martin, principal engineer at Raspberry Pi Trading, tells ZDNet the Pi 400 went into production at Sony's Wales manufacturing facility this July – right in the middle of the first lockdown.

"We signed off around July 2020. That was in full lockdown. We started building up inventory to the point where we have enough to announce the product, which was announced November 2nd," explains Martin. But the history of the device goes back a lot further.

Raspberry Pi CEO Eben Upton had been kicking around the idea of a keyboard computer since 2016, according to Martin.

By early 2017, the company had concept drawings for the keyboard computer and hired Martin in mid-2017 to bring the concept to reality.

Indeed, the first Raspberry Pi keyboard computer could have been a 'Pi 300'.

"At the time Pi 3B+ was the big thing, so I made a Pi 3 prototype of the device. I guess you could call that a Pi 300," he says.

But the project got snagged on the Pi 4's scheduled release for June 2019. By the time that the Pi 300 would be ready to announce, the more powerful Raspberry Pi 4 would already be on the market with significant changes to the line-up.

For the first time since the initial Raspberry Pi in 2012, the computer came with three RAM options spanning 1GB, 2GB and 4GB; previously it was only available with 1GB of RAM.

"We looked at the schedule and realized the Pi 4 was going to come out before the Pi 300, so we decided it was going to look like a runner up and not be very exciting. So we had to cancel the Pi 3 version, and just pressed ahead with the keyboard and hub in 2019," he says.

The Raspberry Pi keyboard looks almost identical to the Pi 400 but connects via micro USB to an external Raspberry Pi. "That was pretty successful," he adds.

Martin then continued to work on the Pi 400 with an "almost complete" Raspberry Pi 4 design.

"The first six months we needed to solve the thermals of this thing and we actually had some really scary high predictions of maximum power – as much as 12 watts. And that kind of scared me because that's in the territory where you start to need fans and all sorts of things," says Martin.

He had a first working prototype in October 2019 with a heat sink. According to Martin, each of the prototypes cost £1,500 ($1997) to make. It took another 10 months to sign-off on a production deal with Sony's factory in Pencoed, Wales, which has manufactured the Raspberry Pi single board computer since 2012.

But by the time he was ready to ink a Pi 400 deal with Sony, much of the world including the UK was in lockdown due to the COVID-19 pandemic. "That's how it took four years," says Martin.

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Redesigning the Raspberry Pi 4's printed circuit board to fit the Pi 400 in some ways wasn't that big a deal, says Martin, but it still took him eight weeks to get the layout right.

"I took a lot of the Pi 4 layout blocks – things like the processor and memory. There was a lot of effort into making that good. So instead of restarting it, I just took the entire block of all the wiring between those two parts and dropped them into my design.

"The same went for the power supply circuit as well. I didn't want to redesign it, I wanted to just drop it into this board. If you look very carefully at the Pi 4 and Pi 400 circuit board, you'll see they're exactly the same layout of components in that area."

Some people have commented that the Pi 400 is a left-handed computer because of the position of the USB ports on the left side of the back of the keyboard. Why put all the USB ports, add-on port, and HDMI ports on the back instead of putting some on the side?

The main reason was to keep the cost of production down. After all, making a computer that costs just $70, based on a board that retails for $55, might require some trade-offs.

"One of the more contentious things we've had on the keyboard is the port selection. It's been tough," he says.

Manufacturer Sony gave Martin three tips to keep production costs down: first, have purely a surface-mount design, second, use as few screws as possible. "The third option we were told was to make sure all connectors are on the back of the unit, so no connectors down the side of the unit," Martin recalls. Having all the ports on one side allowed Sony to automate the assembly and testing process to a far higher degree than if they were on two sides.

"If we had connectors on the side we have to plug it in at the back and then have some complex system to align connectors at the side to plug in as well. It all just becomes quite involved as a system. There'd be lots of drop-out, lots of failures, lots of trouble in the factory. Sony said, just put all the connectors on the back," says Martin.

Martin said Rasperry Pi tried to make as much of the Pi 400 in the UK as possible. "It simplifies the logistics of everything – quality control and so on, it's all in the same country."

The red keyboard base was made in the UK, but for that top, Martin had to look to China.

"There's quite a fiddly mechanism underneath each key that would be very difficult to achieve on a first run. So we just had to make that part in China," says Martin.

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The other part from China is the metal heatsink to dissipate heat generated by the Pi 400's 1.8GHz SoC in the enclosure.

"We looked into making the heatsink in the UK and we just couldn't get a good price. We really, really tried and it just came much easier from China and at a much better price. There aren't any quality control issues we have to worry about on that part. It just works."

So is the Raspberry Pi 400 a forerunner to an actual laptop? Sadly, for Raspberry Pi fans, it's highly unlikely the company will venture down that path any time soon.

"If you were to do a laptop, we'd have to look at more advanced air cooling, we'd need to know how to deal with batteries, displays, echo cancellation of microphones, and all sorts of cables and hinges," says Martin.

"We actually don't have the knowledge base to do that at present, so at the moment there aren't any plans to do such a thing."

The main goal for now is meeting demand and ramping up production of the Pi 400, which is currently available with UK and US English keyboards, as well as Spanish, French, German, and Italian.

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