Where did the Inspiration Come From?

Most people mistakenly take Raspberry Pi products as open source just because of the excellent publicly available documentation and the sheer amount of user using them, but Raspberry Pi Foundation is not completely open source (neither the Raspberry Pi 3 / 4  nor the Raspberry Pi Pico). That’s one of the reason why there is not a single clone of Raspberry Pi boards unlike the Arduino boards.

What if as a learner we get access to a complete open source microcontroller development board and also with added improvements? This trends is most noticeable on Arduino board, where people with passion build lots of variant’s of the same board with lot and lots of features.

This is where MITAYI comes into picture, a potential Gollum’s Ring (Hobbit).

MITAYI Pico v0.2

MITAYI: The Name

Giving the board an Indian flavour, Vishnu named it Mitayi.  It is a Malayalam word മിഠായി (IPA-EN: miṭhāyi) which translates to “candy”. Vishnu inspired this idea from various naming convention like most noticeable on Android series – Jellybean, KitKat, Lollipop, Marshmallow, etc. So he wanted to make a Malayali + Indian taste for the RP2040 boards with the name Mitayi.

Mitayi

Mitayi boards will be exclusively based on the RP2040 microcontroller from Raspberry Pi. Mitayi Pico will be the first one in this series. Following it will come the Mitayi Nano, Mitayi Micro, Mitayi Stamp, and more. While the Mitayi boards are exclusively based on the RP2040 microcontroller from Raspberry Pi, the Mitayi Pico offers enhanced features than Raspberry Pico.

The differences as highlighted here:

Feature	Mitayi Pico r0.2	Raspberry Pi Pico
USB	Micro USB or Type-C USB	Only Micro USB
Flash Memory	16MB, SOIC-8 package	2MB, USON-8
Reset Button	Yes	No
Bootsel Button	No (pad only)	Yes
GPIO Pins	Breaks out all GPIO	Does not break out all pins
Voltage Regulator	Dual Linear 500mA LDO and 1A AMS1117	800 mA buck-boost switching regulator
Component Silkscreen Reference	Yes	No
Smallest component size	0402	0201
Completely Open-source?	Yes	No

Designing and Development

All the Mitayi boards currently available or under pre-release stage are open source. Thus their designs are easily accessible on Github. Also the board is designed using open source EDA tool KiCad, version 6 for very easy access.

Laying Out the Schematics of the Board:

The Mityai design mostly align with the official Pico in terms of their schematics. However, few design references were picked from Shawn Hymel’s Pico Debugger Shoe. Further, they have made sure to maintain its original form factor even with design modifications so that it maintains compatibility with Pi Pico based boards.

Mityai Schematics

As we the whole board is build around RP2040, there are some various interesting choice during the design stage. The flash memory used is the W25Q128JVSSIQ which will help in programming the RP2040 as it does not a flash memory of it’s own. Now to keep the dev board more in trend this board as both Micro USB and Type-C USB receptacle options which is very interesting and we’ll discuss more on that in PCB Layout section.

For power the main 3.3V regulator is an MIC5219-3.3YM5 from Microchip and then a secondary 3.3V regulator NCP1117-3.3 that you can use instead of the more expensive MIC5219 by make to the connection on the jumper. You can read more about it on article released by Circuitstate.

Picking of Ingredients to Complete the Mitayi

When asked about selection of parts and their procurements, Vishnu Mohanan shared his thought process behind it. For the company, the priority was cost, specs, availability and accessibility while selecting the parts. Thus, apart from RP2040, all other parts were chosen based on their local availability. 

For purchasing passives, discrete, and connectors, he also provided the sites and vendors which are easily approachable (In India) such as- 

• ComKey.in
• SUNROM Electronics
• Ktron
• Evelta Electronics

PCB Design

The PCB of the microcontroller development board is the foundation on which sits everything. It is 51x21mm sized, 1mm thick and 2 layered PCB. The location and orientation of the RP2040 is kept the same as the official Pico. 

Due to its miniature size, almost precision is required in every detail on the board from vias to holes:

• The default track thickness and minimum clearance were 0.2 mm. 
• All vias have the same size of 0.5mm/0.3mm (diameter/drill).
• For the pin headers with castellated holes,  simply modify a 20-pin pin header footprint with a 2.54 mm pitch. 
• Minimum hole size is 0.3mm.

Mitayi PCB without components

We really love the stacking Type-C and Micro USB connectors. The footprints did not create any conflicts when placed on top of each other. Many can use this trick to find which port is compatible for your design just by doing one prototype. Though Vishnu was sceptical about type-C and micro USB stacking, the footprints and the routing, everything went pretty smooth and relatively easy. 

Note : During assembly there might be some shorting of USB line because of the metal body of Type-C. To prevent this shortening of the USB line, Kapton tape should be placed on the micro USB footprint before placing the Type-C port. This might be struggle for production, but a neat trick if you are prototyping.

Stacked USB connector footprints

The PCB manufacturing was carried out by PCBWay and it cost the around US $55.00, Since the project was sponsored it was free of cost at the time of production.

Manual Assembly

Vishnu manually assembled the whole PCB rather than assembling them with the fabricator as it would become very expensive when went through further design changes.

It’s nearly impossible to assemble all components on a PCB of such small size using a soldering iron due to the QFN package and 0402 components. Even steady hands could barely do it. Thus, a hot air or a reflow plate is mandatory.

The major challenge was to solder and fix small components on the PCB, because most of the components were dislocated from their footprints during the hot plate reflow process.

Issues during assembly

After tackling all the challenges, the manual assembly of the PCB was completed and post testing, it functioned satisfactorily as we heard from the Vishnu.

The Mitayi with the Sweet Sensation on Electronic Palate

Initiative like this from Circuitstate Electronics help in constantly upgrading the technology to make our electronics world more inclusive and accessible to all. Mitayi series is one such prominent example and the fact that the Mitayi Pico is just their first product in line of many more to come leaves a sweetening satisfaction worth of a Mitayi (candy) in every learner’s electronic palate. 

As we speak there are lots of design changes going on with Mityai Pico, so watch out for more updates!

A huge thanks to Vishnu Mohanan for providing all the images that we used in this article.