Cobalt 3, a pocket computer DIY

A fancy pocket computer you can build yourself with simple through-hole components

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I wanted a pocket computer I can build myself to learn through-hole soldering and get a simple basic computer.
There were a lot of projects out there, ok, but I needed a kit ready to mount, without having to look for components around the world.
The core component is the Atmega328, the keyboard is serial with tactile momentary switches and the display an is a SPI OLED type with the common SH1106 driver. A toggle switch and a led complete the Cobalt 3 (giving a name was the most cool part of the job). I put all together in the design of a simple pcb and I used an Arduino IDE to compile the O.S. in C++ language. The O.S. can be loaded through a UART serial interface. The O.S. is composed of 3 parts: one to show data on the display (data output), one to manage the keyboard (data input), and last but not least, to elaborate the Basic Language instructions (data elaboration).

I started soldering little electronics kits and not without some difficulties. When I thought to be ready to level up, I found out it was too complicated for me to solder and get working a complete computer kit I can buy on a website like Tindie. There were a lot of projects out there, ok, but I needed a kit ready to mount, without having to look for components around the world.  

At that stage the learning curve was too steep, I needed a loophole. So came the idea for my project, creating something that I can also provide to other hobbyists as a simple kit with instruction.

What was the best way? The idea was to start with most familiar electronic components for my objective.

I tried not to modify the software I used and to mantain it original, but I had to make several changes to make all parts work together. Credits go to all developers of Tiny Basic, of Arduino libraries, of Tiny Lisp Computer, of Keymap library, SPI and SH1106 drivers, etc. Thanks to all.  
I learned a lot making this project, and I think many newbies as me would enjoy soldering a kit like this and learn something new.


Executing the Fibonacci series with my #Cobalt3 pocket computer. Video

MPEG-4 Video - 6.03 MB - 06/02/2020 at 16:30


Schematic Cobalt 3 - Basic Pocket Computer_2020-05-31.pdf

The schematic diagram of the pcb. I use the tool EasyEDA to design the circuit

Adobe Portable Document Format - 139.94 kB - 05/31/2020 at 21:49



how is simple to connect usb to TTL to serial port to load the O.S.

MPEG-4 Video - 13.65 MB - 05/30/2020 at 15:39


  • 1 × Oled Display 128x64 SPI 7 pins
  • 1 × AAA battery holder
  • 1 × led Fiber Optics / Emitters
  • 40 × tactile momentary switches
  • 1 × 220 Ohm resistor

View all 15 components

View all 7 project logs

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teraz wrote 01/02/2022 at 22:25 point

how long this device work? a month?

meybe is possible upgrade procesor for fuzux os?

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robert_crofts wrote 07/01/2021 at 15:56 point

Hello there, brilliant kit! I'm going to make it with the kids.

Are there any examples of what BASIC programmes can be done? I'm looking for some inspiration, so would be great to see what others have done.

I'm sure some creative people will push the boundaries... they always do ;) 

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Anthony DiGirolamo wrote 06/06/2020 at 18:34 point

Great project! Thank you for sharing! I really like the board layout and small part count. Maybe if you make a new revision add a gpio expander to read the keyboard over i2c. That would free up some pins and let you have extra headers for connecting this to sensors or as a controller for other projects.

What are those button covers you are using? They look very comfortable for typing on.

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Leonardo Leoni wrote 06/06/2020 at 22:49 point

thank you. You had a great idea to obtain some free pins !

You can find the caps here:

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Grégory Paul wrote 06/05/2020 at 11:40 point

Really cool project !
Do you have any plans to sell only the PCB on tindie ?
I would be very interested to buy it without components (that I already own).

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Leonardo Leoni wrote 06/06/2020 at 10:39 point

Thank you! I'm waiting for the last pcb version. Then I have to test it, and eventually to fix it again. When It will be ready, I will contact you 

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Leonardo Leoni wrote 06/23/2020 at 09:48 point

Hi, I finally completed the testing process. The PCB can be order using gerber files, they are availabe on project repo 

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tormozedison wrote 06/05/2020 at 06:13 point

Greetings. A cool project, but its Github page does not contain firmware. Please add it. Thanks.

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Leonardo Leoni wrote 06/05/2020 at 08:38 point

Thank you! the code it's almost finished and it will be available next August, it's open source

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Adam Quantrill wrote 06/04/2020 at 18:41 point

I like the look of it but my immediate observation is - why not offset the keys on a diagonal like on a real qwerty keyboard?  Even the ZX80 did this and although I don't expect to be able to touch type on this, it would at least make finger aiming slightly more accurate.

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Leonardo Leoni wrote 06/04/2020 at 19:05 point

you're totally right Adam! It's just my choice, I preferred this design

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rxt1077 wrote 06/04/2020 at 15:34 point

This is awesome! Any plans on making a kit for it? 

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Leonardo Leoni wrote 06/04/2020 at 19:11 point

Cobalt 3 pocket computer DIY is listed on Tindie! You can join the waitlist, It's almost finished

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Leonardo Leoni wrote 06/02/2020 at 23:20 point

Hpag, you can use a 3.7v AAA battery. 

3.7 volts are necessary to make the Cobalt3 working

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Carlos Suárez wrote 06/02/2020 at 04:07 point

Excellent project! Which quartz crystal are you using? I'm excited. When can I download your PCB?

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Leonardo Leoni wrote 06/02/2020 at 16:17 point

the quartz crystal oscillator is a standard 16.000 Mhz. It's available the schematic diagram, while other files will be available in next months. Thank you Carlos

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Gabriel wrote 05/31/2020 at 22:59 point

cool project! Id like to ask you what battery and bat. holder part numbers you are using. Looks like a 14500 liion?

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Leonardo Leoni wrote 05/31/2020 at 23:16 point

thank you! The battery is more little, AAA standard, 10440 Li-Ion 3.7v, rechargeable (eventually you need a recharger). This board consumes very little energy so it's sufficient a 350 or 600 mAh battery

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Hpag wrote 06/02/2020 at 22:50 point

So that means we can also use a regular AAA battery on it, right?

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Gabriel wrote 06/08/2020 at 04:07 point

Where did you buy them?

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Leonardo Leoni wrote 06/08/2020 at 07:18 point

you can buy it on Aliexpress

  Are you sure? yes | no

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