Archives August 2019

Project Roadmap

In this log, we want to share our experience of bringing our FunKey Project from its early-prototype stage to a “Ready For Manufacturing” / “Community-Ready” state necessary to launch a successful crowdfunding campaign that in turn should provide us with the lever required to launch a product in mass production.

Where Do We Come From

People following the Funkey Project certainly remember that the original motivation came from @Sprite_tm‘s 2016 Hackaday superconference project of a pocket retro gaming console, that lead @c.Invent to develop the #Keymu – open source keychain-sized gaming console as a Proof-of-Concept that entered the 2017 Hackaday Prize. The corresponding Youtube video is now peaking at 4.8M views and #6 in Youtube’s Popular Videos – Game Consoles & Mobile Phones category!

Unfortunately, the tiny (and expensive) Intel Edison CPU module at the heart of the console was abruptly discontinued, which forced him to find a replacement module. Given the tiny dimensions, this prove to be very difficult, but @Squonk42 joined him to develop a new board around the LicheePi Zero module. Eventually, a new #Funkey Zero console which was used to validate the new CPU choice took part in the 2018 Hackaday Prize:

At this point, it became clear that the main feature of the #Keymu – open source keychain-sized gaming console was its foldable design, providing a maximum size for both the screen and keypads in the smallest form factor. It also became clear that such a hinged design required the help of a professional mechanical designer, and this challenge motivated @David.Larbi who joined the team at the beginning of this year. Read More

Layout: Screen FPC Extender

LCD Screen

The chosen LCD screen for the FunKey console is awesome:


The FunKey console uses a foldable design in order to reduce the device size when not in use, and maximize both the screen and keypad size when playing. The screen flat cable must then go into the hinge, and in order to avoid too much stress that would eventually lead to broken cables, it must be “rolled” into it like a flypaper in order to divide the stress over the longest possible length.

Unfortunately, the stock LCD screen ribbon cable is not long enough. This is of course something that the manufacturer can customize, but this costs a fixed tooling fee of $800… We plan to go this way for mass production, but this sounds like a lot of money for the prototyping phase only.

FPC Extender

So, we decided to use cheaper alternatives for our prototypes:

  • for the Revision A, we used individually soldered thin enameled copper wires and an ultra small PCB placed into the hinge: definitely not something to use for more than 2 boards!
  • for the Revision B, we decided to invest some money into a customized FPC (Flat Printed Cable) as we can get 5x FPC prototypes for ~$100 at PCBWay

The problem is: I never designed FPCs before 😉

I got some basic hints from one of my colleague:

  • the copper density must be as constant as possible
  • the traces must use smooth curves instead of sharp angles to avoid tearing during flexion

However, a few questions remained unanswered:

  1. what material and thickness to use for the stiffeners?
  2. what material and thickness for the flex itself?
  3. which stack-up?

I decided to crawl the Web for more information, and here is what I found, I hope this may help some other PCB designers: Read More

Layout: Screen FPC Extender Update

The previous log detailed the screen FPC extender, used to adapt the stock LCD screen to the FunKey main PCB.

Before launching the FPC fabrication which is quite expensive (~ $100 / 5 pieces), we decided to have a dry run using a paper mock-up. Here is the result:

We covered the old Rev. A PCB with a paper print of the new Rev. B one, and created a paper version of the flex, gluing the connectors on them at the right positions. As you can see, the result is not too bad.

This was until we tried to open the lid flat:

Well, the FPC is a little bit too long, causing a “wave” that totally defeats the original purpose of the “flypaper design”: the small bend radius would certainly cause a failure sooner or later.

Moreover, the FPC is a little bit too wide, too, so it interferes with the internal ribs somehow.

So, back to the drawing board, we decreased the length by 2 mm, and the width to 4 mm, here is the result:

Much better! And the behavior when opening / closing the lid is also improved:

Here are the corresponding layouts:

Meet the team

I tried different angles to approach this log, and writing about us from a third person’s point of view simply wouldn’t work. It was too detached for my taste and it felt hypocritical writing things about myself as another’s POV. Instead I chose the 1st person narrative to talk about our team, “I” meaning “Vincent” in this case. It feels more genuine, and I get to really “tell” our story this way.

FunKey’s project is currently composed of three people which, by order or arrival in the team, are: Vincent (myself) Michel and David. Since we are a small team, the best way to present all of us is simply through FunKey’s story, so here it goes:


As some of you may know Funkey started out as a project submitted during the 2017 Hackaday Prize called Keymu. Before explaining why I undertook such a project, let me quickly go over some of my background.

Originally, I studied telecommunications during my master’s in France. Telecommunications is a vast topic that encompasses many areas such as informatics, electronics, networking, signal processing… I specialized in the latter, and during my last year abroad, I quickly drifted towards computer vision, a topic that never ceases to amaze me. After the master’s, I actually continued in this branch during my PhD.

So, yeah, I was a research scholar, in Computer Vision and Machine Learning at the time, pretty far from electronics…

Something always felt missing though, all this high-level knowledge felt shallow without the low-level one. Computer vision is often used on embedded products, allowing them to “see” the world and understand it for us, faster than us. I simply felt the need to know how to build the machines for which we developed these algorithms, in order to understand the whole chain. After my PhD then, I started working as an embedded engineer for a company in France. This is where I met Michel and David for the first time.

When, a few months later, Hackaday published an article about SpriteTM’s tiny console, it was love at first sight. I wanted very badly to build one, not just to own it but because it called to my inner retro-gamer instincts and it was a great way to learn about electronics and embedded software. At the time SpriteTM did not release yet any of the code or designs, hence Keymu was born.

I quickly realized, I undertook something way bigger than expected for a first “side project”. It was completely different than SpriteTM’s design: it was based on a computer module, I needed to develop a custom linux distribution (very different code than for microprocessors, especially the drivers), the mechanical hinge was harder than expected…This is when Michel entered into play.


It is safe to say that Keymu might have never hatched without him. Apart from helping me with the electronical design, every roadblock I met seemed only small bumps before his incredible experience. He followed the design and all the new ideas from the start, started himself installing the environment for developing the Linux distribution with Yocto, proposed solutions to many encountered problems… All in all, he was already part of the team from the start, he apeared only “officially” in the team during our next project: FunKey Zero but it is simply formalities.

For the purpose of this log, I have asked my partners to present themselves through small bios. Since I started this first narrative point of view, it feels only logical to keep it throughout the log, that is why I prefer to restranscribe their bios as they’ve been provided.

Here is Michel’s:

I started my engineering experience at age 2 (back in 1968) by inserting metallic knitting needles into a live wall socket.

I stumbled upon my first computer (Goupil 2) in January 1980. Shortly after that (and for quite a long time), I got my second computer: an Apple II, still in love with it! I developed my first expansion board for it to hook a Teletype Model 33 from 1963 as a daisy wheel printer over 20mA current loop. I have been developing both hardware and software at the same time since then.

My first Unix steps were in 1984, using a CU connection to the university PDP11. I switched to Amiga 1000 in 1986, and worked mainly on 68k-based custom-made computers until 1996, with lots of business travels worldwide (spent 1 1/2 year in Atlanta, GA, USA during the Olympic Games in 1996).

I discovered Linux 0.9.x in 1994 (Thx to Pierre Ficheux). In 2002 I wrote the iPaq Linux Howto: and since then have used mostly Linux-based systems for my personal work.

I Reverse-engineered the TL-WR703 pocket router hardware in 2012: and

In April 2014 I started the project ( “An Open Hardware WiFi Platform for Things”). We launched a successful Kickstarter campaign in April 2015, with all products delivered to users (almost) on time. They are still available from GL-Inet shop, eBay and Amazon

A lot of experience indeed. At this point I left back FunKey’s story at FunKey Zero. For those who do not know this project, we hit a real roadblock with Keymu, one that could not be overcome this time: the main computer module (Intel Edison) had been discontinuited. In order to improve Keymu, we then developped a board with everything new: processor, storage, display, sound, power management,…

This board was part of our FunKey Zero project submitted in 2018 and was meant to focus on software and electrical development only. We knew Keymu’s hinged design was the only way to go to optimize screen size, buttons thickness, and battery’s autonomy but Michel and I simply did not have enough mechanical design experience to build something fit for production, especially with an active hinge.

This is when David entered the team.


To be completely fair, David already knew about Keymu since he helped giving advice when I worked on the mechanical design. After FunKey Zero, we again asked for help reviewing our design and I remember David being instantly on boad (he told me at the time that the project looked really “funky” without even knowing the name was “Funkey”). He was in search of interesting projects to work with, and we were in search for a professional mechanical engineer: it was a perfect match.

As before, here is his bio in his own words:

I have found my calling at age 14 when my parents offered me an electronic discovery kit (before that I wanted to be a road train driver).

To this end I have studied electronic for 9 years. During my last three years of studies, I have discovered electro manufacturing services (EMS) for the first time and had the chance to program my first SMT machine: the CP6 from FUJI: CHIP SHOOTER.
I then worked for 14 years for a company selling cameras designed for industrial applications and scanners for ancient manuscripts.

It is during this time that I have made the switch from electronic design to mechanical design as I self-taught myself how to use SOLIDWORKS. After many hours, I learned to master it and started developing professional mechanical designs.

In 2017, I started my own company ( a mechanical design office specializing in the integration of electronics, the design of plastic injection parts and additive technologies. Projects I designed with my clients are mainly IoT products as well as manual tools (plastic cutters, ZAMAC or magnesium).

I remain passionate and curious about technology in general. The FunKey Project is an adventure full of opportunities to discover and learn. An occasion to conceive, build and sell a very fun product among a pluridisciplinar team, all revolving around a great topic: the retro-gaming.

Back to the story: since then we are equally working on FunKey’s project, as well regarding our respective abilities (software, electrical design, mechanical design) as regarding all other aspects of the project (website, social networks, newsletter, this hackaday page, publicity, emails, commands, production…)

We all have day-to-day jobs but we are working hard during our free time to try and make FunKey a reality.

FunKey Revision B is out!

Here it is: the FunKey Revision B is eventually out!

You can find the corresponding design file ZIP and schematics in PDF in the “File” section.

FunKey Revision A Board

We consider FunKey Revision A board as an “alpha test” board. We built 2 units using manual pick & place and a small T962 reflow oven.

Except for a few bad solder joints, the only real problem we encountered is a wrong value for the R11 DDR RAM equalization resistor (was 240k instead of 240R). Another minor problem was a wrong footprint for transistor Q1 (was SOT323 instead of SOT23)

We can consider it as a success, as the boards worked (almost) out of the box and we were able to mount them into a 3D-printed case and make some nice videos out of them.

However, assembling this board manually doesn’t scale up very nicely: as these are dual-sided PCBs, the boards needs to go twice in the oven, using solder paste with different reflow temperatures, and just placing the 175 components on each board takes hours and a lot of patience…

We thus decided to move to…

FunKey Revision B Board

The goals for this revision were:

  • correct the Revision A bugs
  • make some mechanical adjustments required to ease the FunKey assembly into the case
  • replace some components to reduce the BOM cost
  • add test pads for a better testability
  • outsource the PCB Assembly (PCBA)
  • avoid over-engineering a working board!

Bug Corrections

As discussed above, the only physical changes were to replace the value for the R11 DDR RAM equalization resistor (was 240k instead of 240R) in the BOM and to change the footprint for transistor Q1 (was SOT323 instead of SOT23).

A few quirks in the schematics were corrected:

  • the “START” and “SELECT” signal labels were swapped (now also renamed to “START” and “FUN”)
  • the comment for R8 was referencing the wrong chip (U2, now U3)
  • some signal labels around U5 were not the same size as all other labels

Mechanical Adjustments

Although we were able to mount the Revision A PCB into the 3D-case, we found some minor assembly problems:

  • the 1.5 mm headroom over the PCB button side was too low over some components (the power inductor L6 and the transistor Q1): L6 has been moved to the other PCB side with all components for the DRAM Power, and the Q1 transistor was moved away from the buttons
  • the screen connector has been moved to be in front of the hinge flex opening and turned 180° to expose all the active pins to on the PCB edge side
  • consequently, the UART and battery connectors have been shuffled around, and the battery connector moved away from the screw well to provide more room to bend the battery wires
  • the 2x Omron B3U-3000P(M) rear buttons have been replaced because they were too fragile and did not provide a good feedback when pressed. We now use 2x Panasonic EVP-AVAA1A, which are the right-angle equivalent of the EVP-BB2A9B000 we have for the top buttons. These buttons are backed by the PCB edge so they have no chance to break if pushed too hard, and their haptic feedback is really good
  • the speaker mounting was tedious: we tried to avoid having to solder wires, but the PCB thickness of 0.8 mm was too important to provide a way to bridge the gap between the trace and the speaker pad with a solder blob, we had to use some TH resistor wire to do the connection:

    We changed the design to use castellated pads (“half-moon” plated holes on the PCB edge) positioned farther just over the speaker pads, so the distance between the PCB copper pad and the speaker pad is now zero and allows soldering the speaker with just a small solder bridge

Component Sourcing

The FunKey Revision A board used mostly components available from major online distributors, ( we ordered them from Mouser, as they are today significantly cheaper than Radiospares, Farnell or even Digi-Key). OTOH, some exotic components (the Allwinner V3s CPU, the AXP209 PMIC and the microUSB connector) had to be sourced from AliExpress, as they were not available anywhere else at a cheaper price.

But mostly, the FunKey Revision A board should be considered as a “western” board, whose components are not optimized to be produced in China, which will be our final production country for obvious cost reasons.

We took the opportunity to roll out the FunKey Revision B to switch to mostly Chinese suppliers whenever possible. We found most of the components at and its Chinese sister website

The price difference there is significant, as passive components are 10x cheaper, connectors are 5x to 6x cheaper, and you can find some equivalent DC/DC or PMIC chips at a fraction of their western price. Another way of saving money is to avoid crossing borders: in this case, you’d better buy the components to mount on the PCB in China from China, if possible.

However, there are some components we still had to provision from global online distributors:

  • the L3/L4/L5 power inductors
  • the 0603 current measurement resistor R21
  • all the EVP-BB2A9B000 and EVP-AVAA1A (R/A) tactile switches as the required quantity was not in stock from LCSC
  • the S14 MEDER MK24 Reed switch (more on this later in this article!)
  • the SP1 CUI CDM-10008 speaker
  • the PCAL6416AHF,128 I2C GPIO expander U1
  • the PAM8301AAF audio amplifier U3

All other passive components were replaced by some available at LCSC, but not necessarily the cheapest ones: we chose the “cheapest available in quantity” ones instead, to make sure we don’t have to switch to another reference later.

We found equivalent parts for the MicroUSB and MicroSD card connectors and for the DRAM DC/DC U4, as well as for the crystals Y1/Y2. the AXP209 PMIC U5 was directly available there, too.

Only the Allwinner V3s CPU U3 had still to be sourced from Alibaba.

With these component changes, we are now confident that we can reach our target electronic BOM cost for MP (Mass Production).

PCBA Tests

Another very important point to consider in order to get a product that is RFM (Ready For Manufacturing) is to make sure to have a good test plan for the PCB/PCBA: you cannot count on everything working as expected without a glitch on thousands of pieces!

Of course you may ask the PCB manufacturer to perform 100% electrical test on the naked PCB using “flying probes”, but another important issue is to make sure the final PCBA (PCB Assembly) is good too.

The technique most suitable given our expected production quantities and board characteristics (small size and dual-sided) is to use test jigs with some retractable interfaces featuring either mating connectors and/or spring-loaded “Po-Go” pins that will make contacts with corresponding test pads on the PCB.

On the FunKey Revision A PCB, we already had some test pads, but they prove too small to be useful. For Revision B, we increased their size to 1 mm diameter, and we made sure to have all important signals available on the least populated PCB side (the button side).

We started to define a progressive test plan to check that all the parts on the assembled PCB perform as desired, using as little as possible steps and test vectors to make the test procedure as fast as possible: time is money on a production line!

Having a good test plan defined early in the design phase is a key point to reduce defects during MP.

Outsourced PCBA

As said earlier, the FunKey Revision A boards were assembled by us using a small reflow oven.

One major goal of the FunKey Revision B is to make sure that the board assembly can be outsourced, meaning that we are able to provide all the required information for this task, yet another key step towards a successful MP.

We took the opportunity of the limited-time (now over since July 31st) offer from SeeedStudio for free assembly for 5 pieces.

Conforming to SeedStudio requirements for gerbers files, pick and place files, assembly drawing and BOM file took us some considerable amount of time, but eventually, this will certainly help us to formalize the PCBA procedure for MP too.

We are still waiting to receive the boards that were approved for manufacturing, we cross our fingers and toes, hoping everything will go as expected!

New Features!

We tried very hard to avoid adding more features to the existing FunKey Revision A design that is working, but hey, we are engineers, after all!

But in order to avoid adding bugs by over-engineering the board, we limited them to 2 low-risk changes:

  • we added a separate LCD_RESET line for the LCD (just a single wire with a pull-up resistor R29, so we can reset the LCD without having to reset the whole board in case something goes bad with the display
  • we added a magnetic Reed switch S14 to the AXP209 PMIC’s N_OE (Negative Output Enable) input, in order to suspend the FunKey console after a delay when the lid is closed, and resume it back to where it stopped when the lid is opened again:


Given its limited design changes and large improvements in terms of electrical BOM cost optimization, testability and assembly outsourcing capabilities, the FunKey Revision B board must be considered as a “beta test” board, which is an important milestone towards our goal to produce the FunKey retro gaming console in large quantities in China.