COMIX-35 Assembly Resources

Project page to document the resources and assembly of a COMIX-35

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This project page is intended to document where to purchase the components necessary for the assembly of a COMIX-35, a RCA CDP1802 based computer system designed by TubeTimeUS.

The COMIX-35 is an open-source clone of the 1980s COMX-35 8-bit home computer. It uses the RCA 1802 microprocessor which is strange and slow but holds the distinction of being the first CMOS microprocessor. The "35" is because the original computer has 32K of main memory + 3K of video RAM.

There are a number of differences between the COMIX-35 and the original:

  • Single +5V power supply
  • Uses SRAM; no stolen cycles for DRAM refresh
  • Configurable PAL or NTSC by changing three jumpers and swapping a crystal
  • Additional CPU crystal for a new turbo mode
  • Mechanical key switches for your typing comfort
  • Cassette input data light indicates incoming information

View all 9 components

  • Space Bar Stabilizer Assembly

    Dave's Dev Lab03/26/2021 at 00:09 0 comments

    The space bar stabilizer can be a bit tricky to assemble properly. With that in mind, I took a few pictures to document the process. The stabilizer comes with five pieces: a wire bar, two mounting tabs, and two riser tabs.

    The two mounting tabs and the two riser tabs need to be assembled. They are not keyed but there is a right way and wrong way to assemble them. The assembly on the left in this picture is correct. The riser tab should be free to move all the way out of the mounting tab. The assembly on the right is incorrect, and does not allow for full travel of the riser tab.

    Once the mounting tab and riser tab are assembled together, you will need to insert the assembly into the PCB. The "peg" portion goes to the smaller hole and the "clip" to the larger hole. you will notice an opening on the side of the assembly which will face to the edge of the board. Placing the "clip" into the larger hole, and push the "peg" into the smaller hole. You should feel a soft "click" when it snaps into place.

    Once both assemblies are snapped into place you can insert the wire bar into the opening and snap the wire bar into the retaining clip.

    After doing both sides, you are ready to place the spacebar keycap on top. Just make sure that the pegs for both assemblies and the keyboard switch are properly inserted into the slots on the underside of the keycap!

  • Keyboard Switch Selection

    Dave's Dev Lab03/25/2021 at 22:14 0 comments

    If you go shopping for keyboard switches, you will find a ton of them listed on Amazon and Ebay. The most common advertised are the 5-pin and 3-pin versions. Both will work on the COMIX-35, however unlike the 5-pin version, the 3-pin version does not have guide posts. The guide posts are essential for proper alignment of the switch on the PCB. If you  use the 3-pin version, you will need to spend a lot of effort to manually place the switch on the PCB and solder it. The 5-pin version "snaps" into the PCB and self aligns, so I recommend you go with the 5-pin version, which I have listed in the parts section...

  • Flux Removal Before Keyboard Switches

    Dave's Dev Lab03/25/2021 at 21:51 0 comments

    The keyboard switches arrived earlier this week, but before I install them, I needed to do some flux removal on the components already on the PCB. They keyboard switches aren't sealed, so soaking the board in flux remover would allow some to get into the internal structure of the switches. The flux remover I am using is a specialty product from MG Chemicals that costs about $20USD for 945mL at Amazon. After soldering in the switches, I can use a flux remover pen to target the switch solder points without getting any into the internals of the switches... 

  • Keyboard Switches and Caps Arrived!

    Dave's Dev Lab03/22/2021 at 18:39 0 comments

    The keyboard switches and key caps arrived today! i'll do a post about each separately!

  • Resistance is Futile!

    Dave's Dev Lab03/19/2021 at 04:39 0 comments

    Well... I got everything populated and validated except for the resistors. There were a few minor hiccups with the mouser bill-of-materials that I have already updated. Overall it looks pretty good! can't wait for the switches, keycaps and IC kit to arrive!

  • A Word about Tools

    Dave's Dev Lab03/18/2021 at 22:28 0 comments

    Along with information about parts used for the assembly of the COMIX-35, I'll add in some recommendations for tools and other secondary items that will help your assembly process. The first one I want to recommend is that you have a really good set of wire cutters. Most of the components will come with long wire leads that will need to be trimmed after soldering them in place. These Plato wire cutters are super sharp and make quick clean work of trimming the leads. They are available on Amazon with prime shipping of a two pack for $11USD.

  • Assembly Started!

    Dave's Dev Lab03/18/2021 at 22:06 0 comments

    The plan is to start at the top of the Bill-of-Materials (BOM) and work the way down. First on the list are the capacitors. I'll probably skip a few items, like the connectors,  which would make it difficult to balance the board on the desktop while soldering. So one line item down, about 50 more to go! Fun Fun Fun!!!

  • Mouser Parts Arrived!

    Dave's Dev Lab03/18/2021 at 20:56 0 comments

    The Mouser Bill-of-Materials (BOM) arrived today! I already had a significant portion of these parts already, but I wanted to validate the BOM as it is uploaded to Mouser. I'll start work on assembly this weekend and check each part against the BOM as I solder in the part. This way we can be sure that the BOM as uploaded to Mouser is 100% correct. As a side note, a good portion of these parts, including the CDP1802 are available from surplus retailer BGMicro. I like to use vendors like BGMicro when I can as they are a great resource for retro electronics!

  • Space Bar Stabilizer Parts

    Dave's Dev Lab03/18/2021 at 00:46 0 comments

    I ordered in eight different products that were listed on Amazon that might be possible replacements for the "Space Bar Stabilizer" that is out of stock at Mouser. It isn't the cheapest one at $14USD, but it is available with Prime shipping and appears to be have plenty in stock. Other sets that I ordered have much slower delivery times but better pricing at around $8USD. I'll post an update when they arrive. The installation of these stabilizer parts is kind of unintuitive, so I'll post some installing instructions and pictures later...

  • Parts Ordered!

    Dave's Dev Lab03/12/2021 at 02:46 0 comments

    Well i've ordered the IC kit from ebay, the key caps and switches from amazon, and the rest of the components from Mouser! i'll be able to verify each the parts once they arrive to make sure all of the info is correct. there are several pieces still in question, but i should be able to evaluate them once they arrive!

View all 12 project logs

Enjoy this project?



Nazwa wrote 06/22/2022 at 22:00 point

this device can run fuzix?

  Are you sure? yes | no

Dave's Dev Lab wrote 06/22/2022 at 22:03 point

sorry, i don't believe this is a supported system for fuzix, you can check the fuzix website for supported CPU and systems...

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Anestis wrote 06/22/2022 at 07:22 point

Here you may find the STL files for the 3D case I have designed and a number of images of my "makes" :-)

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Dave's Dev Lab wrote 06/22/2022 at 16:31 point

awesome addition! i'll add it to the resources!

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Frank wrote 05/22/2021 at 10:13 point

hi, I built the board from GitHub on powering up I get a screen full of ‘9’s cycling through four colours, any help appreciated.  Thanks

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Dave's Dev Lab wrote 05/23/2021 at 22:45 point

sorry i'm not able to provide any feedback on this...

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Justin Davis wrote 03/18/2021 at 00:16 point

more retrocomputer projects need a built-in keyboard.  I approve!

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[this comment has been deleted]

Dave's Dev Lab wrote 03/14/2021 at 17:39 point

this is a replica of the COMX-35 computer -

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Dan Maloney wrote 03/12/2021 at 19:43 point

Pretty cool, I had a COSMAC-VIP back in the day that I'd love to build a replica of. Ran a CDP-1802 and it was my first exposure to machine coding.

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Andrew Wasson wrote 03/26/2021 at 14:54 point


You might need to get a VIP2K:

There are several retro kits worth getting from Lee. He’s got some neat stuff.

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zpekic wrote 03/11/2021 at 03:54 point

Great project resurrecting an interesting computer! Btw, not sure if aware, there is a little community of retro-computing fans from ex-Yugoslavia tinkering with Pecom-32/64 which were very similar to COMIX-35, to the point that probably most Basic programs could run on both:

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Dave's Dev Lab wrote 03/11/2021 at 03:58 point

thanks for the comment, as noted above, the COMIX-35 isn't my design or project, i'm just documenting where to get all the components for the assembly and any "gotchas" on doing the assembly. the author's github page is linked above...

  Are you sure? yes | no

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