Z80 Retro Cobra computer
This cool looking 8-bit computer is based on core design that reaches back 1984. Upgraded in 21st century with capability to display colorful text and graphics on monitor screen and running games became a popular choice for retro computing electronics enthusiast.
Equipped with AY3-8910 sound chip, joystick port, PS/2 socket and cartridge port, it ensures continues fun thanks for new software and games actively developed by Cobra community. Easy to build from readily available TTL-series logic chips, it can be part of your collection with small effort.
History behind Cobra
The Cobra-1 computer was designed in the early 1980s by two Polish engineers, Andrzej Sirko and Grzegorz Gancarz. At that time, during the Cold War in Eastern Europe, access to electronic components—especially integrated circuits—was severely limited. Despite the difficult circumstances, the two engineers overcame significant obstacles to develop the design and build a working prototype. Their success earned Cobra a notable place in the history of Polish computing.
The first version of Cobra, designated "1", was published in the popular magazine Audio-Video as part of a series of articles. These articles described the system architecture, hardware design, construction process, and included software examples—such as a BASIC language interpreter. Schematics and PCB layouts were provided for readers bold enough to take on the challenge of building the computer themselves.
It is important to note that the cost of parts needed to build the Cobra at that time was significant equivalent to one to two years of the average salary. This was due to the stark disparity between Eastern European wages and the cost of electronic components manufactured in the West.
The price ratio often ranged from 1:6 to as high as 1:10, depending on the type of product. For example, a Commodore 64 that sold for $299 in the U.S. could cost the equivalent of $2,999 at launch in Eastern Europe. Who could afford that in the mid-1980s? Certainly not the average home user.
Cobra Specifications
* Z80 CPU running 6.5MHz or 3.25MHz
* 512kB Flash ROM
64kB general purpose
* 4kB+2kB (dual port) Video RAM
* 512kB Video Flash ROM for user definable fonts
* AY3-8910 Two Cannel audio
* 56-key built in keyboard
* RGBS Video output
* Composite Video output
* PS/2 port for external keyboard
(mouse in works)
* Joystick port
* Tape recorder In/Out RCA x 2
* Cartridge port
* Internal BUS extension port
* SD Card slot
* Headphone output (3.5mm jack)
* Power jack (5V @ 2A)
System architecture
Cobra, as a microcomputer, was a significantly simplified version of a larger system designed and built by engineer Andrzej Sirko between 1979 and 1981. A photograph of this original system appeared in one of the early issues of Audio-Video magazine (issue no. 2/84). The system ran on the CP/M operating system and used an 8-inch floppy drive. It featured separate boards for the CPU, RAM, video, and several other modules.
Cobra Color is a modernized version of the original design, based on the Cobra-1 core from 1984, with added support for color video and sound. The user-definable Flash ROM was expanded to 512 kB and operates in software-controlled page mode, allowing storage of multiple operating systems (such as Cobra Monitor, Cobra DOS, and CP/M), programming languages (Cobra BASIC, Assembler), and commonly used applications.
The externally accessible cartridge port serves as a convenient alternative to the built-in Flash ROM, allowing users to insert their own flashed cartridges to override the internal ROM and run custom operating systems or applications.
The Cobra community gathered around popular in Poland "Elektroda" portal periodically releases Flash ROM updates that introduce new features and fix bugs. These updates often include additional demos and games that developers are actively working on. So far, there have been 14 official Cobra ROM releases, with the next one currently in development.
Click "e" logo to visit Elektroda portal.
Community development & support
The Cobra project is a living ecosystem of hardware, software, and a dedicated developer community working to keep the computer alive. Since the community is primarily maintained in a foreign language, we will be providing updates in English on this website, covering all developments related to software packages—including Flash ROM content releases. The full repository of packages developed so far will be made available here shortly.
Click picture to visit Cobra 1 thread on Elektroda forum
Design roots
The original Cobra-1 design was based on hand-drawn schematics. At one point, a community member recreated these using Microsoft Paint. While the resulting image was much clearer, editing the JPEG format remained difficult. In the early 2000s, another community member transferred the PCB design into KiCAD. The schematics for an intermediate version of Cobra soon followed. Color graphics were introduced in the second decade of the 21st century, when the Cobra project was revived after being dormant throughout the 1990s and 2000s. Due to the absence of a complete project repository after 40 years of the Cobra’s existence, I decided—at the end of 2024—to assemble one myself. This turned out to be a time-consuming, yet challenging and exciting journey.
2025 Resurrection
My work began in early 2025 with transferring the schematics of the Cobra Color version (referred to as the "2023" edition) from a PNG image into Altium Designer format.
The PCB design followed shortly after. For this, I used Gerber files from a package that had previously been prototyped and built at least once by a few members of the Cobra community. This significantly reduced the risk of working with an untested design.
By early spring 2025, I had the schematics and PCB fully synchronized in Altium, with zero DRC (Design Rule Check) errors. This became the baseline for future development and ongoing maintenance of the Cobra project.
Around that time, I chose to replace a feature from the original design—an LED bar graph circuit, whose purpose was unclear to me—with a user-addressable alphanumeric display based on micro-LED technology from Broadcom. This new solution connected the spirit of early electronics design—recalling the golden era of Nixie tube indicators—with a modern implementation using an uncommon but intriguing format: a 5x8 matrix of 40 micro-LED cells.
What I retained on the keyboard was the secondary 3-position 7-segment LED display, originally used to indicate the index of the active video generator ROM character set. As noted in the specifications, Cobra uses a 512 kB video ROM, which allows the user to store multiple character sets—and add even more as needed. This secondary display helps identify the currently selected set during software debugging, especially when switching between the more than one hundred sets stored in the video ROM. Although this feature is not essential for everyday user operations, it is a valuable tool for developers when verifying which character generator set is active during code debugging.
Prototype build
At this point, it became clear that I needed to build a prototype of the Cobra Color computer based on the transferred design, to validate its content and ensure my work had not been in vain.
Ordering the PCBs was straightforward, and within a few days, I received two large, printed circuit boards: a red motherboard and a white keyboard. The motherboard PCB was upgraded with two internal planes—one for VCC and one for GND—which significantly reduced parasitic impedance along the power supply paths between multiple ICs. It also increased the board’s decoupling capacity, which was especially important given the large number of mixed TTL and CMOS components used in this relatively complex design.
I decided to keep the keyboard PCB as a 2-layer design, since the large key matrix didn’t require dedicated power or return rails.
To finalize the key layout, I needed to choose an available keycap set to avoid building a keyboard that would be difficult to fit with factory-made, aesthetically pleasing keycaps. After some research, I selected an off-the-shelf keycap set that offered a popular layout in a variety of colors. Although there were many options, I chose one that ensured consistent key size and alignment across the entire keyboard.
For the actual key switches, I selected reliable Cherry switches with center post that keeps part in place centered, releasing mechanical stress from the solder pins during use, enduring long keyboard reliability and longevity. Small tradeoff I had to make was in the Space bar key where I used two switches instead of hard to source mechanical bracket that holds Space key levelled during typing. The 2-switch approach results in twice as high force needed to press the key vs. single keys but I found that difference insignificant during use.
My version of Cobra Color keyboard has a handful of special keys that are user definable like Alt, Ctrl or Super. On order to use them not only software application must process their codes but also user must physically hook these up to unused key address/data spots on the key matrix. The table below shows special keys assignment I decided to apply in my Cobra prototype.
With all parts in place, I connected both boards and flashed the main system ROM and the video ROM—then powered it up. The system started immediately after turning on.
A minor adjustment to the horizontal sync trigger cleared up the display, and the video quality on the RGB output turned out to be more than pleasing.
With a working set of electronics, it was time to complete the build with an enclosure. Since the PCBs were custom-sized and uniquely shaped, I decided to design a custom case specifically for 3D printing.
First design cut was meant to be 3D printed using small printer therefore model contained two halves, left and right for each clamshell part. This changed soon after I realized large format designs can be 3D printed by couple of popular vendors without compromising on quality and price.
The first version of the case was printable, but the top half of the "breadbox" proved prone to random warping, especially around the edges of the keyboard opening.
The solution was to add reinforcement ribs around the perimeter of the keys to strengthen the structure.
With the help of a few clever design tricks, my SolidWorks-expert friend managed to pull everything together. The second 3D-printed enclosure turned out to be usable—although not perfect. This time, it was free from warping, but the top half had shrunk slightly, by just a hairline. Even so, assembling both halves was still possible. The final result was solid and mechanically sound—more than good enough for showcasing the Cobra Color to an older, retro-computing audience.
The finishing touch was the logo sticker, which I designed myself and had printed at a local print shop as a thick, domed "pillow" sticker.
The overall result turned out to be more than satisfactory.
Affixing it to the freshly printed enclosure gave me a real sense of accomplishment. In the professional world of project management, I would call that a “gate event”—a clear milestone that marked the completion of a significant phase of this "40 yrs in making" project.
The Cobra-Color is undergoing extensive testing and once it is complete, it may become available as set of PCB FABs or DIY kit.
Stay tuned!
Thanks for visiting.
