Raspberry Pi has always been a PC company. Inspired by the home computers of the 1980s, our mission is to put affordable, high-performance, programmable computers into the hands of people all over the world. And inspired by these classic PCs, here is Raspberry Pi 400: a complete personal computer, built into a compact keyboard.
Raspberry Pi 4, which we launched in June last year, is roughly forty times as powerful as the original Raspberry Pi, and offers an experience that is indistinguishable from a legacy PC for the majority of users. Particularly since the start of the COVID-19 pandemic, we’ve seen a rapid increase in the use of Raspberry Pi 4 for home working and studying.
But user friendliness is about more than performance: it can also be about form factor. In particular, having fewer objects on your desk makes for a simpler set-up experience. Classic home computers – BBC Micros, ZX Spectrums, Commodore Amigas, and the rest – integrated the motherboard directly into the keyboard. No separate system unit and case; no keyboard cable. Just a computer, a power supply, a monitor cable, and (sometimes) a mouse.
Raspberry Pi 400
We’ve never been shy about borrowing a good idea. Which brings us to Raspberry Pi 400: it’s a faster, cooler 4GB Raspberry Pi 4, integrated into a compact keyboard. Priced at just $70 for the computer on its own, or $100 for a ready-to-go kit, if you’re looking for an affordable PC for day-to-day use this is the Raspberry Pi for you.
Buy the kit
The Raspberry Pi 400 Personal Computer Kit is the “Christmas morning” product, with the best possible out-of-box experience: a complete PC which plugs into your TV or monitor. The kit comprises:
A Raspberry Pi 400 computer
Our official USB mouse
Our official USB-C power supply
An SD card with Raspberry Pi OS pre-installed
A micro HDMI to HDMI cable
The official Raspberry Pi Beginner’s Guide
At launch, we are supporting English (UK and US), French, Italian, German, and Spanish keyboard layouts, with (for the first time) translated versions of the Beginner’s Guide. In the near future, we plan to support the same set of languages as our official keyboard.
Buy the computer
Saving money by bringing your own peripherals has always been part of the Raspberry Pi ethos. If you already have the other bits of the kit, you can buy a Raspberry Pi 400 computer on its own for just $70.
Buy the book
To accompany Raspberry Pi 400, we’ve released a fourth edition of our popular Raspberry Pi Beginner’s Guide, packed with updated material to help you get the most out of your new PC.
You can buy a copy of the Beginner’s Guide today from the Raspberry Pi Press store, or download a free PDF.
Where to buy Raspberry Pi 400
UK, US, and French Raspberry Pi 400 kits and computers are available to buy right now. Italian, German, and Spanish units are on their way to Raspberry Pi Approved Resellers, who should have them in stock in the next week.
We expect that Approved Resellers in India, Australia, and New Zealand will have kits and computers in stock by the end of the year. We’re rapidly rolling out compliance certification for other territories too, so that Raspberry Pi 400 will be available around the world in the first few months of 2021.
Of course, if you’re anywhere near Cambridge, you can head over to the Raspberry Pi Store to pick up your Raspberry Pi 400 today.
What does everyone else think?
We let a handful of people take an early look at Raspberry Pi 400 so they could try it out and pull together their thoughts to share with you. Here’s what some of them made of it.
Simon Martin, who has spent the last couple of years bringing Raspberry Pi 400 to life, will be here tomorrow to share some of the interesting technical challenges that he encountered along the way. In the meantime, start thinking about what you’ll do with your Raspberry Pi PC.
How do you create a 3D model of a historic graveyard? With eight Raspberry Pi computers, as Rob Zwetsloot discovers in the latest issue of The MagPi magazine, out now.
“In the city centre of Dundee is a historical burial ground, The Howff,” says Daniel Muirhead. We should probably clarify that he’s a 3D artist. “This old graveyard is densely packed with around 1500 gravestones and other funerary monuments, which happens to make it an excellent technical challenge for photogrammetry photo capture.”
This architecture, stone paths, and vibrant flora is why Daniel ended up creating a 3D-scanning rig out of eight Raspberry Pi computers. And the results are quite stunning.
“The goal of this project was to capture photos for use in generating a 3D model of the ground,” he continues. “That model will be used as a base for attaching individual gravestone models and eventually building up a full composite model of this complex subject. The ground model will also be purposed for rendering an ultra-high-resolution map of the graveyard. The historical graveyard has a very active community group that are engaged in its study and digitisation, the Dundee Howff Conservation Group, so I will be sharing my digital outputs with them.”
To move the rig throughout the graveyard, Daniel used himself as the major moving part. With the eight Raspberry Pi cameras taking a photo every two seconds, he was able to capture over 180,000 photos over 13 hours of capture sessions.
“The rig was held above my head and the cameras were angled in such a way as to occlude me from view, so I was not captured in the photographs which instead were focused on the ground,” he explains. “Of the eight cameras, four were the regular model with 53.5 ° horizontal field of view (FoV), and the other four were a wide-angle model with 120 ° FoV. These were arranged on the rig pointing outwards in eight different directions, alternating regular and wide-angle, all angled at a similar pitch down towards the ground. During capture, the rig was rotated by +45 ° for every second position, so that the wide-angles were facing where the regulars had been facing on the previous capture, and vice versa.” Daniel worked according to a very specific grid pattern, staying in one spot for five seconds at a time, with the hopes that at the end he’d have every patch of ground photographed from 16 different positions and angles.
“With a lot of photo data to scan through for something fairly complex, we wondered how well the system had worked. Daniel tells us the only problems he had were with some bug fixing on his code: “The images were separated into batches of around 10,000 (1250 photos from each of the eight cameras), plugged into the photogrammetry software, and the software had no problem in reconstructing the ground as a 3D model.”
Accessible 3D surveying
He’s now working towards making it accessible and low-cost to others that might want it. “Low-cost in the triple sense of financial, labour, and time,” he clarifies. “I have logged around 8000 hours in a variety of photogrammetry softwares, in the process capturing over 300,000 photos with a regular camera for use in such files, so I have some experience in this area.”
“With the current state of technology, it should be possible with around £1000 in equipment to perform a terrestrial photo-survey of a town centre in under an hour, then with a combined total of maybe three hours’ manual processing and 20 hours’ automated computer processing, generate a high-quality 3D model, the total production time being under 24 hours. It should be entirely plausible for a local community group to use such a method to perform weekly (or at least monthly) 3D snapshots of their town centre.”
We love seeing how quickly our community of makers responds when we drop a new product, and one of the fastest off the starting block when we released the new Raspberry Pi Compute Module 4 on Monday was YouTuber Jeff Geerling.
We made him keep it a secret until launch day after we snuck one to him early so we could see what one of YouTube’s chief advocates for our Compute Module line thought of our newest baby.
So how does our newest board compare to its predecessor, Compute Module 3+? In Jeff’s first video (above) he reviews some of Compute Module 4’s new features, and he has gone into tons more detail in this blog post.
Jeff also took to live stream for a Q&A (above) covering some of the most asked questions about Compute Module 4, and sharing some more features he missed in his initial review video.
His next video (above) is pretty cool. Jeff explains:
“Everyone knows you can overclock the Pi 4. But what happens when you overclock a Compute Module 4? The results surprised me!”
And again, there’s tons more detail on temperature measurement, storage performance, and more on Jeff’s blog.
Top job, Jeff. We have our eyes on your channel for more videos on Compute Module 4, coming soon.
Explore our new free pathway of environmental digital making projects for young people! These new step-by-step projects teach learners Scratch coding and include real-world data — from data about the impact of deforestation on wildlife to sea turtle tracking information.
By following along with the digital making projects online, young people will discover how they can use technology to protect our planet, all while improving their computing skills.
The projects help young people affect change
In the projects, learners are introduced to 5 of the United Nations’ 17 Sustainable Development Goals (SDGs) with an environment focus:
Affordable and Clean Energy
Responsible Consumption and Production
Life Below Water
Life on Land
Technology, science, maths, geography, and design all play a part in the projects. Following along with the digital making projects, young people learn coding and computing skills while drawing on a range of data from across the world. In this way they will discover how computing can be harnessed to collect environmental data, to explore causes of environmental degradation, to see how humans influence the environment, and ultimately to mitigate negative effects.
Where does the real-world data come from?
To help us develop these environmental digital making projects, we reached out to a number of organisations with green credentials:
We asked the team behind the Ecosia search engine, profits from which get invested in sustainability projects, for their guidance on growing trees. You can watch Ecosia software engineer Jessica Greene chat to us on our weekly Digital Making at Home live stream for young people.
Inspiring young people about coding with real-world data
The digital making projects, created with 9- to 11-year-old learners in mind, support young people on a step-by-step pathway to develop their skills gradually. Using the block-based visual programming language Scratch, learners build on programming foundations such as sequencing, loops, variables, and selection. The project pathway is designed so that learners can apply what they learned in earlier projects when following along with later projects!
We’re really excited to help learners explore the relationship between technology and the environment with these new digital making projects. Connecting their learning to real-world scenarios not only allows young people to build their knowledge of computing, but also gives them the opportunity to affect change and make a difference to their world!
Discover the new digital making projects yourself!
With Green goals, learners create an animation to present the United Nations’ environment-focused Sustainable Development Goals.
Through Save the shark, young people explore sharks’ favourite food source (fish, not humans!), as well as the impact of plastic in the sea, which harms sharks in their natural ocean habitat.
With the Tree life simulator project guide, learners create a project that shows the impact of land management and deforestation on trees, wildlife, and the environment.
Computers can be used to study wildlife in areas where it’s not practical to do so in person. In Count the creatures, learners create a wildlife camera using their computer’s camera and Scratch’s new video sensing extension!
Electricity is important. After all, it powers the computer that learners are using! In Electricity generation, learners input real data about the type and amount of natural resources countries across the world use to generate electricity, and they then compare the results using an animated data visualisation.
Understanding the movements of endangered turtles helps to protect these wonderful animals. In this new Turtle tracker project, learners use tracking data from real-life turtles to map their movements off the coast of West Africa.
Code along wherever you are!
All of our projects are free to access online at any time and include step-by-step instructions. They can be undertaken in a club, classroom, or at home. Young people can share the project they create with their peers, friends, family, and the wider Scratch community.
It’s amazing how we’ve come from everything being keyboard-based to so much voice control in our lives. Siri, Alexa, and Cortana are everywhere and happy to answer questions, play you music, or help automate your household.
For the keen maker, these offerings may not be ideal for augmenting their latest project as they are closed systems. The good news is, with a bit of help from Google, you can add voice recognition to your project and have complete control over what happens. You just need a Raspberry Pi 4, a speaker array, and a Google account to get started.
Set up your microphone
For a home assistant device, being able to hear you clearly is an essential. Many microphones are either too low-quality for the task, or are unidirectional: they only hear well in one direction. To the rescue comes Seeed’s ReSpeaker, an array of four microphones with some clever digital processing to provide the kind of listening capability normally found on an Amazon Echo device or Google Assistant. It’s also in a convenient HAT form factor, and comes with a ring of twelve RGB LEDs, so you can add visual effects too. Start with a Raspberry Pi OS Lite installation, and follow these instructions to get your ReSpeaker ready for use.
You’ll see later on that we can add the power of Google’s speech-to-text API by streaming audio over the internet. However, we don’t want to be doing that all the time. Snowboy is an offline ‘hotword’ detector. We can have Snowboy running all the time, and when your choice of word is ‘heard’, we switch to Google’s system for accurate processing. Snowboy can only handle a few words, so we only use it for the ‘trigger’ words. It’s not the friendliest of installations so, to get you up and running, we’ve provided step-by-step instructions.
Create your own hotword
As we’ve just mentioned, we can have a hotword (or trigger word) to activate full speech recognition so we can stay offline. To do this, Snowboy must be trained to understand the word chosen. The code that describes the word (and specifically your pronunciation of it) is called the model. Luckily, this whole process is handled for you at snowboy.kitt.ai, where you can create a model file in a matter of minutes and download it. Just say your choice of words three times, and you’re done. Transfer the model to your Raspberry Pi 4 and place it in your home directory.
Let’s go Google
After the trigger word is heard, we want Google’s fleet of super-servers to help us transcribe what is being said. To use Google’s speech-to-text API, you will need to create a Google application and give it permissions to use the API. When you create the application, you will be given the opportunity to download ‘credentials’ (a small text file) which will allow your setup to use the Google API. Please note that you will need a billable account for this, although you get one hour of free speech-to-text per month. Full instructions on how to get set up can be found here.
Install the SDK and transcriber
To use Google’s API, we need to install the firm’s speech-to-text SDK for Python so we can stream audio and get the results. On the command line, run the following:pip3 install google-cloud-speech (If you get an error, run sudo apt install python3-pip then try again). Remember that credentials file? We need to tell the SDK where it is: export GOOGLE_APPLICATION_CREDENTIALS="/home/pi/[FILE_NAME].json" (Don’t forget to replace [FILE_NAME] with the actual name of the JSON file.) Now download and run this test file. Try saying something and see what happens!
Putting it all together
Now we can talk to our Raspberry Pi, it’s time to link the hotword system to the Google transcription service to create our very own virtual assistant. We’ve provided sample code so that you can see these two systems running together. Run it, then say your chosen hotword. Now ask ‘what time is it?’ to get a response. (Don’t forget to connect a speaker to the audio output if you’re not using HDMI.) Now it’s over to you. Try adding code to respond to certain commands such as ‘turn the light on’, or ‘what time is it?’
Get HackSpace magazine 36 Out Now!
Each month, HackSpace magazine brings you the best projects, tips, tricks and tutorials from the makersphere. You can get it from the Raspberry Pi Press online store, The Raspberry Pi store in Cambridge, or your local newsagents.
Every year, we support the PA Raspberry Pi Competition for UK schools, run by PA Consulting. In this free competition, teams of students from schools all over the UK imagine, design, and create Raspberry Pi–powered inventions.
The PA Raspberry Pi Competition aims to inspire young people aged 8 to 18 to learn STEM skills, teamwork, and creativity, and to move toward a career in STEM.
We invite all UK teachers to register if you have students at your school who would love to take part!
Among all the entries, judges from the tech sector and the Raspberry Pi Foundation choose the finalists with the most outstanding inventions in their age group.
The final teams get to take part in an exciting awards event to present their creations so that the final winners can be selected. This round’s PA Raspberry Pi Awards Ceremony takes place on Wednesday 28 April 2021, and PA Consulting are currently considering whether this will be a physical or virtual event.
All teams that participate in the competition will be rewarded with certificates, and there’s of course the chance to win trophies and prizes too!
You can prepare with our free online courses
If you would like to boost your skills so you can better support your team, then sign up to one of our free online courses designed for educators:
Find out more at the PA Raspberry Pi Competition webinar!
To support teachers in guiding their teams through the competition, PA Consulting will hold a webinar on 12 November 2020 at 4.30–5.30pm. Sign up to hear first-hand what’s involved in taking part in the PA Raspberry Pi Competition, and use the opportunity to ask questions!
In computing education research, considerable focus has been put on the design of teaching materials and learning resources, and investigating how young people learn computing concepts. But there has been less focus on assessment, particularly assessment for learning, which is called formative assessment. As classroom teachers are engaged in assessment activities all the time, it’s pretty strange that researchers in the area of computing and computer science in school have not put a lot of focus on this.
That’s why in our most recent seminar, we were delighted to hear about formative assessment — assessment for learning — from Dr Shuchi Grover, of Looking Glass Ventures and Stanford University in the USA. Shuchi has a long track record of work in the learning sciences (called education research in the UK), and her contribution in the area of computational thinking has been hugely influential and widely drawn on in subsequent research.
Two types of assessment
Assessment is typically divided into two types:
Summative assessment (i.e. assessing what has been learned), which typically takes place through examinations, final coursework, projects, etcetera.
Formative assessment (i.e. assessment for learning), which is not aimed at giving grades and typically takes place through questioning, observation, plenary classroom activities, and dialogue with students.
Through formative assessment, teachers seek to find out where students are at, in order to use that information both to direct their preparation for the next teaching activities and to give students useful feedback to help them progress. Formative assessment can be used to surface misconceptions (or alternate conceptions) and for diagnosis of student difficulties.
As Shuchi outlined in her talk, a variety of activities can be used for formative assessment, for example:
Self- and peer-assessment activities (commonly used in schools).
Different forms of questioning and quizzes to support learning (not graded tests).
Rubrics and self-explanations (for assessing projects).
A framework for formative assessment
Shuchi described her own research in this topic, including a framework she has developed for formative assessment. This comprises three pillars:
Teacher or classroom practice.
The role of the community in furthering assessment practice.
Shuchi’s presentation then focused on part of the first pillar in the framework: types of assessments, and particularly types of multiple-choice questions that can be automatically marked or graded using software tools. Tools obviously don’t replace teachers, but they can be really useful for providing timely and short-turnaround feedback for students.
As part of formative assessment, carefully chosen questions can also be used to reveal students’ misconceptions about the subject matter — these are called diagnostic questions. Shuchi discussed how in a classroom setting, teachers can employ this kind of question to help them decide what to focus on in future lessons, and to understand their students’ alternate or different conceptions of a topic.
Formative assessment of programming skills
The remainder of the seminar focused on the formative assessment of programming skills. There are many ways of assessing developing programming skills (see Shuchi’s slides), including Parsons problems, microworlds, hotspot items, rubrics (for artifacts), and multiple-choice questions. As an MCQ example, in the figure below you can see some snippets of block-based code, which students need to read and work out what the outcome of running the snippets will be.
Questions such as this highlight that it’s important for learners to engage in code comprehension and code reading activities when learning to program. This really underlines the fact that such assessment exercises can be used to support learning just as much as to monitor progress.
Formative assessment: our support for teachers
Interestingly, Shuchi commented that in her experience, teachers in the UK are more used to using code reading activities than US teachers. This may be because code comprehension activities are embedded into the curriculum materials and support for pedagogy, both of which the Raspberry Pi Foundation developed as part of the National Centre for Computing Education in England. We explicitly share approaches to teaching programming that incorporate code reading, for example the PRIMM approach. Moreover, our work in the Raspberry Pi Foundation includes the Isaac Computer Science online learning platform for A level computer science students and teachers, which is centered around different types of questions designed as tools for learning.
All these materials are freely available to teachers wherever they are based.
Further work on formative assessment
Based on her work in US classrooms researching this topic, Shuchi’s call to action for teachers was to pay attention to formative assessment in computer science classrooms and to investigate what useful tools can support them to give feedback to students about their learning.
Shuchi is currently involved in an NSF-funded research project called CS Assess to further develop formative assessment in computer science via a community of educators. For further reading, there are two chapters related to formative assessment in computer science classrooms in the recently published book Computer Science in K-12 edited by Shuchi.
There was much to take away from this seminar, and we are really grateful to Shuchi for her input and look forward to hearing more about her developing project.
Join our next seminar
If you missed the seminar, you can find the presentation slides and a recording of the Shuchi’s talk on our seminars page.
In our next seminar on Tuesday 3 November at 17:00–18:30 BST / 12:00–13:30 EDT / 9:00–10:30 PT / 18:00–19:30 CEST, I will be presenting my work on PRIMM, particularly focusing on language and talk in programming lessons. To join, simply sign up with your name and email address.
I am delighted to share the news that we have appointed a new Chair and Trustees of the Raspberry Pi Foundation. Between them, they bring an enormous range of experience and expertise to what is already a fantastic Board of Trustees, and I am really looking forward to working with them.
New Chair of the Board of Trustees: John Lazar
John Lazar has been appointed as the new Chair of the Board of Trustees. John is a software engineer and business leader who is focused on combining technology and entrepreneurship to generate lasting positive impact.
Formerly the Chairman and CEO of Metaswitch Networks, John is now an angel investor, startup mentor, non-executive chairman and board director, including serving as the Chair of What3Words. He is a Fellow of the Royal Academy of Engineering and played an active role in developing the programme of study for England’s school Computer Science curriculum. John has also spent many years working on tech-related non-profit initiatives in Africa and co-founded Enza Capital, which invests in early-stage African technology companies that solve pressing problems.
John takes over the Chair from David Cleevely, who has reached the end of his two three-year terms as Trustee and Chair of the Foundation. David has made a huge contribution to the Foundation over that time, and we are delighted that he will continue to be involved in our work as one of the founding members of the Supporters Club.
New Trustees: Amali de Alwis, Charles Leadbeater, Dan Labbad
Alongside John, we are welcoming three new Trustees to the Board of Trustees:
Amali de Alwis is the UK Managing Director of Microsoft for Startups, and is the former CEO of Code First: Girls. She is also a Board member at Ada National College for Digital Skills, sits on the Diversity & Inclusion Board at the Institute of Coding, is an Advisory Board member at the Founders Academy, and was a founding member at Tech Talent Charter.
Charles Leadbeater is an independent author, a social entrepreneur, and a leading authority on innovation and creativity. He has advised companies, cities, and governments around the world on innovation strategy and has researched and written extensively on innovation in education. Charles is also a Trustee of the Paul Hamlyn Foundation.
Dan Labbad is Chief Executive and Executive Member of the Board of The Crown Estate. He was previously at Lendlease, where he was Chief Executive Officer of Europe from 2009. Dan is also a Director of The Hornery Institute and Ark Schools.
New Member: Suranga Chandratillake
I am also delighted to announce that we have appointed Suranga Chandratillake as a Member of the Raspberry Pi Foundation. Suranga is a technologist, entrepreneur, and investor.
He founded the intelligent search company blinkx and is now a General Partner at Balderton Capital. Suranga is a Fellow of the Royal Academy of Engineering and a World Economic Forum Young Global Leader, and he serves on the UK Government’s Council for Science and Technology.
What is a Board of Trustees anyway?
As a charity, the Raspberry Pi Foundation is governed by a Board of Trustees who is ultimately responsible for what we do and how we are run. It is the Trustees’ job to make sure that we are focused on our mission, which for us means helping more people learn about computing, computer science, and related subjects. The Trustees also have all the usual responsibilities of company directors, including making sure that we use our resources effectively. As Chief Executive, I am accountable to the Board of Trustees.
We’ve always been fortunate to attract the most amazing people to serve as Trustees and, as volunteers, they are incredibly generous with their time, sharing their expertise and experience on a wide range of issues. They are an important part of the team. Trustees serve for up to two terms of three years so that we always have fresh views and experience to draw on.
How do you appoint Trustees?
Appointments to the Board of Trustees follow open recruitment and selection processes that are overseen by the Foundation’s Nominations Committee, supported by independent external advisers. Our aim is to appoint Trustees who bring different backgrounds, perspectives, and lived experience, as well as a range of skills. As with all appointments, we consider diversity at every aspect of the recruitment and selection processes.
Formally, Trustees are elected by the Foundation’s Members at our Annual General Meeting. This year’s AGM took place last week on Zoom. Members are also volunteers, and they play an important role in holding the Board of Trustees to account, helping to shape our strategy, and acting as advocates for our mission.
Raspberry Pi Compute Module 4 designer Dominic Plunkett was kind enough to let us sit him down for a talk with Eben, before writing up his experience of bringing our latest board to life for today’s blog post. Enjoy.
When I joined Raspberry Pi, James, Eben and Gordon already had some ideas on the features they would like to see on the new Compute Module 4, and it was down to me to take these ideas and turn them into a product. Many people think design is a nice linear process: ideas, schematics, PCB, and then final product. In the real world the design process isn’t like this, and to get the best designs I often try something and iterate around the design loop to get the best possible solution within the constraints.
Form factor change
Previous Compute Modules were all in a 200-pin SODIMM form factor, but two important considerations pushed us to think about moving to a different form factor: the need to expose useful interfaces of the BCM2711 that are not present in earlier SoCs, and the desire to add extra components, which meant we needed to route tracks differently to make space on the PCB for the additional parts.
Breaking out BCM2711’s high-speed interfaces
We knew we wanted to get the extra features of the BCM2711 out to the connector so that users could make use of them in their products. High-speed interfaces like PCIe and HDMI are so fast coming out of the BCM2711 that they need special IO pins that can’t also support GPIO: if we were to change the functionality of a GPIO pin to one of the new high-speed signals, this would break backwards compatibility.
We could consider adding some sort of multiplexer to swap between old and new functionality, but this would cost space on the PCB, as well as reducing the integrity of the fast signals. This consideration alone drives the design to a new pinout. We could have tried to use one of the SODIMM connectors with extra pins; while this would give a board with similar dimensions to the existing Compute Modules, it too would break compatibility.
PCB space for additional components
We also wanted to add extra items to the PCB, so PCB space to put the additional parts was an important consideration. If you look carefully at a Compute Module 3 you can see a lot of tracks carrying signals from one side of the SoC to the pins on the edge connector. These tracks take up valuable PCB space, preventing components being fitted there. We could add extra PCB layers to move these tracks from an outer layer to an inner layer, but these extra layers add to the cost of the product.
This was one of the main drivers in changing to having two connectors on different edges of the board: doing so saves having to route tracks all the way across the PCB. So we arrived at a design that incorporated a rough split of which signals were going to end up on each of the connectors. The exact order of the signals wasn’t yet defined.
Trial PCB layouts
We experimented with trial PCB layouts for the Compute Module 4 and the CM4 IO Board to see how easy it would be to route the signals; even at this stage, the final size of the CM4 hadn’t been fixed. Over time, and after juggling parts around the PCB, I came to a sensible compromise. There were lots of things to consider, including the fact that the taller components had to go on the top side of the PCB.
The pinout was constantly being adjusted to an ordering that was a good compromise for both the CM4 and the IO Board. The IO Board layout was a really important consideration: after we made the first prototype boards, we decided to change the pinout slightly to make PCB layout on the IO Board even easier for the end user.
When the prototype Compute Module 4 IO Boards arrived back from manufacture, the connectors hadn’t arrived in time to be assembled by machine, so I fitted them by hand in the lab. Pro tip: if you have to fit connectors by hand, take your time to ensure they are lined up correctly, and use lots of flux to help the solder flow into the joints. Sometimes people use very small soldering iron tips thinking it will help; in fact, one of the goals of soldering is to get heat into the joint, and if the tip is too small it will be difficult to heat the solder joint sufficiently to make a good connection.
Whilst it was easy to add some headline features like a second HDMI port, other useful features don’t grab as much attention. One example is that we have simplified the powering requirements. Previous Compute Modules required multiple PSUs to power a board, and the power-up sequence had to be exactly correct. Compute Module 4 simply requires a single +5V PSU.
In fact, the simplest possible base board for Compute Module 4 just requires a +5V supply and one of the connectors and nothing else. You would need a CM4 variant with eMMC and wireless connectivity; you can boot the module with the eMMC, wireless connectivity gives you networking, and Bluetooth connectivity gives you access to IO devices. If you do add extra IO devices the CM4 also can provide a +3.3V supply to power those devices, avoiding the need for an external power supply.
We have seen some customers experience issues with adding wireless interfaces to previous Compute Modules, so a really important requirement was to provide the option of wireless support. We wanted to be as flexible as possible, so we have added support for an external antenna. Because radio certification can be a very hard and expensive process, we have a pre-certified external antenna kit that can be supplied with Compute Module 4. This should greatly simplify product certification for end products, although engineering designers should check to make certain of meeting all local requirements.
This is probably the most exciting new interface to come to Compute Module 4. On the existing Raspberry Pi 4, this interface is used internally to add the XHCI controller which provides the USB 3 ports. By providing the PCIe externally, we are giving end users the choice of how they would like to use this interface. Many applications don’t need USB 3 performance, so the end user can make use of it in other ways — for NVMe drives, to take one example.
In order to have wired Ethernet connectivity with previous Compute Modules, you needed to add an external USB-to-Ethernet interface. This adds complexity to the IO board, and one of the aims of the new Compute Module 4 is to make interfacing to it simple. With this in mind, we added a physical Ethernet interface to CM4, and we also took the opportunity to add support for IEEE1588 to this. As a result, adding Gigabit wired networking to CM4 requires only the addition of a magjack; no extra silicon is needed. Because this is a true Gigabit interface, it is also faster than the USB-to-Ethernet interfaces that previous Compute Modules use.
Open-sourcing the Compute Module 4 IO Board design files
Early on in the process, we decided that we were going to open-source the design files for the Compute Module 4 IO Board. We used our big expensive CAD system for Compute Module 4 itself, and while we could have decided to do the design for the IO Board in the big CAD system too and then port it across to KiCAD, it’s easy to introduce issues in the porting process.
So, instead, we used KiCAD for the IO Board from the start, and the design files that come out of KiCAD are the same ones that we use in manufacture. During development I had both CAD systems running at the same time on the computer.
Easier integration and enhanced possibilities
We have made some big changes to our new Compute Module 4 range, and these should make integration much simpler for our customers. Many interfaces now just need a connector and power, and the new form factor should enable people to design more compact and more powerful products. I look forward to seeing what our customers create over the next few years with Compute Module 4.
Get your Compute Module 4
The new Raspberry Pi Compute Module 4 is available from our network of Approved Resellers. Head over to the Compute Module 4 product page and select your preferred variant to find your nearest reseller.
Can’t find a reseller near you? No worries. Many of our Approved Resellers ship internationally, so try a few other locations.
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