8-bit computer
A 8-bit computer i am making for a school project.
Created by
Minecraftchest2
Tier 2
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Timeline
Minecraftchest2
added to the journal ago
fixed the BOM and did a sanity check on the schematic
I went through my BOM again to make sure it was optimized. switched over a few items to LCSC so they where cheaper. also did a sanity check on the schematic to make sure that i didn't make any mistakes on it. asked for another set of eyes to check it over to make sure i didn't miss anything before i route the PCB again.
Kai Pereira 🚀
requested changes for 8-bit computer ago
Hello, could you please optimize your BOM a tad, you have some really expensive caps, and I feel like some of your digikey parts can be bought from LCSC for cheaper! Also look if there's a coupon for 6 layer boards for JLCPCB, as there commonly are, just try to get your project under $150! I'd also like you to get PCB reviews from the KiCad discord server, reddit, and communities that do this kind of thing, or else you're practically gambling on your board working, just add these into your journal! Please also clean up your schematic, and double check everything, there's things like SW4 that looks really sketchy in your schematic!
Minecraftchest2
submitted 8-bit computer for review ago
Minecraftchest2
added to the journal ago
Fix some issues
Updated the readme to have a Screen shot of the PCB in the case (CAD models). Also i updated the BOM to included estimated shipping cost and Tariffs as well as other fees.
Tanook 🚀
requested changes for 8-bit computer ago
Hello! Please include an SS with all the components attached, including the CAD and THT components!
Minecraftchest2
submitted 8-bit computer for review ago
Minecraftchest2
added to the journal ago
Update BOM
Updated BOM to use parts sourced from LCSC. if a part was cheaper on Digikey or Jameco i left it to be ordered from there. I also removed the stencil from my order. i would switch to lead free HASL but JLCPCB doesn't let me choose anything but ENIG for a 6 layer PCB witch with the $20 coupon i am going to use (exspires 04/01/2026) it is $3 cheaper then a 4 layer PCB.
technical_.
requested changes for 8-bit computer ago
As said before, "You don't need a stencil if you are only using THT components. In addition you also don't need ENIG for your THT holes, as you are hand soldering (just make sure that you are using lead free solder). This PCB should have the most standard options. Please source your parts from LCSC, there are much more cheaper options there. If there is a specific reason why you are using Digikey/other vendors, please let me know!". Please note that repeated submissions without clarification to the reviewer or edits to your project can result in a permanent rejection of your project.
Minecraftchest2
submitted 8-bit computer for review ago
technical_.
requested changes for 8-bit computer ago
A couple of problems. You don't need a stencil if you are only using THT components. In addition you also don't need ENIG for your pads, as you are hand soldering (just make sure that you are using lead free solder). This PCB should have the most standard options. Please source your parts from LCSC, there are much more cheaper options there. If there is a specific reason why you are using Digikey/other vendors, please let me know!
8-bit computer was submitted for review ago
Minecraftchest2
added to the journal ago
Rerouted the pcb
While i was working on the BOM for my project i realized that one of the parts i had on my PCB wasn't going to work so i needed to switch to a different chip that is a THT instead witch was also bigger. though sense i didn't really make to many changes to the layout re routing the PCB didn't take to long because i already know how it would work mostly. as long with using a ground and power plane instead of needing to connect via traces witch probably where to small to contain the power and heat anyways.
Minecraftchest2
added to the journal ago
made the case and added the silkscreen art
made a simple case for my project witch is more for keeping the solder joints and the parts on the back off the ground so it is only a base with standoffs and doesn't include a top case. the silk screen art is just QR codes linking to the blueprint page and the github repo.
Minecraftchest2
added to the journal ago
finished routing the PCB
Sense i chose to go with the 6 layer PCB the routing of the signals was easy. the hardest part was trying to find the nets that still needed connected near the end and figuring out the via setup for the areas that need a high amount of level changes in a concentrated areas though i did try to avoid that completely.
now the question is what silkscreen art to add to the blank spaces.
Minecraftchest2
added to the journal ago
Routed the power plane
Routed the power plane of the PCB and like the ground plane it just had a few SMD pins to route.
this was pretty simple because i had figured out how to do it properly already.
Minecraftchest2
added to the journal ago
Routed the gnd plane
sense i did the cost/benefit analysis and found that a 6 layer PCB is worth the extra cost over a 2 layer PCB and sense with the $20 coupon it is actually cheaper then the 4 layer PCB ($3 less but still) i chose to go with a 6 layer pcb to make routing easier. Now i have all of the ground pins routed with only 7 traces that needed to change to the top layer for the 555 timers and 2 other of the same ICs and the USB-C port because they are SMD (i couldn't find any THT footprints for them). next i am going to do the power plane.
Minecraftchest2
added to the journal ago
Fixed all but one of the ERC errors.
I fixed most of the ERC errors witch i probably should have done before i spent a while on the pcb layout but hindsight is 2020. Though it does seem that most of the errors i had where from unconnected pins so they weren't hard to fix.
attached is a screen shot of the last ERC error i have remaining.
Minecraftchest2
added to the journal ago
cleaned up to pcb and started fixing some of the ERC errors
Didn't really get to much done but i now have the PCB mostly layed out and just need to get the traces routed after fixing the ERC errors i have. I have figured out how to get only certain nets to show at a time.
Minecraftchest2
added to the journal ago
remaking the pcb layout
started reworking the pcb layout so i can run the traces manualy without spending a few weeks on it. still quite early but sense i have it set up in as modules it shoun't take me to long once i get each of the modules layed out so they connect together at least semi organised if not optimized.
Minecraftchest2
added to the journal ago
Organised and routed the PCB
I layed out the PCB and got freerouting started on routing the traces so i don't have to manually run nearly 1000 traces. though i have forgot to add the silkscreen to label what buttons and switches are for so i will need to run it again after i do that. though having the buttons and switch uses on a document that goes with the project could also work.
Minecraftchest2
added to the journal ago
Cleaned up schematic and added power input
I did the (rough) calculations for power and figured out that a USB-C port with amperage set to 500 mA will be enough for the power. i also cleaned up the schematic and got the annotations and started getting footprints ready for the PCB design.
Minecraftchest2
added to the journal ago
finnised makeing the schematics
I originally connected everything using busses and wires until i got to the end of my first wiring run at witch point i was using global labels to connect stuff. After i finished everything i realized that i may have messed stuff up because the way i set up the busses might not have worked at witch point i switched to using global labels for connecting over long distances.
Minecraftchest2
added to the journal ago
Set up the cpu control module
I got the schematic for the control module set up. it wasn't very hard though i did need to wire one section of it twice because i did it wrong the first time. though i did take a little bit for me to get all of the sheet pins set up because there are 16 pins that are all different so i couldn't just copy and paste the parts that where the same.
Minecraftchest2
added to the journal ago
Set up the output module
I got the sheet for the output module set up witch besides needing to find a replacement for the 28c16 EEPROM chip. that was its own adventure but digikey was helpful for finding one. i didn't find a full drop in replacement though i have now figured out the naming scheme for EEPROM families.
Over all it was fun to set up. though i do hope that i am using the same symbols becasue the symbols i am using are diffrent pin names then the same pins that the guide i am using has.
Minecraftchest2
added to the journal ago
Made the program counter
I made the program counter witch is the easiest part of the entire project.
For this one the hardest part was just making it look nice witch didn't take to long and wasn't to hard.
Minecraftchest2
added to the journal ago
Made the RAM module
I made the ram module for the PC. but sense i used a custom symbol for one of the chips i need it isn't as clean as i would have hoped but it works.
It was a little harder then the other modules because the custom symbols didn't match the pin names of the symbols on the reference schematic so i needed to make sure that i was matching the pin names and not the pin numbers.
Minecraftchest2
added to the journal ago
Make a symbol for the 74189 ram chip
Sense i couldn't find a symbol or a alternative that works with out extensive upgrades to the rest of the computer i decided to make a symbol biased on data sheet linked to by Ben Eater.
I managed it by essentially copying the connection diagram from the data sheet and turning it into a symbol then using the block diagram to figure out the what pins where outputs.
I figgured out how to use the symbol editor and how to tell what pins are inputs and what pins are outputs.
Minecraftchest2
added to the journal ago
Made the MAR module
I made the schematic for the MAR module witch was pretty easy as non of the parts needed swapped out. I didn't really learn any thing new in the process other then if you hold control you can move things off the grid.
Minecraftchest2
added to the journal ago
Made the scematic for the ALU and flags register
set up the flags register and the ALU schematic. it wasn't to hard to do but i did figure out how to make the schematic look better so it probably looks better then my previous schematics. I also figured out that there is a version control function built into KiCad though i may stick to the command line for the future.
Minecraftchest2
added to the journal ago
layed out the schematic for the a-register and b-register
I got the a-register schematic layed out and all the connections set up. sense i just needed to grab the components and nothing was really hard to find it didn't take to hard to make. sense the b register is basically the same (the only difference is the output names) I just copied the existing schematic file and hierarchical sheet and edited it to make it work.
Minecraftchest2
added to the journal ago
Set up the clock module
Made the clock module schematic following the schematic that Ben Eater made. It took me a little bit for me to figure out what RV1 was turns out it was a Potentiometer. I have also stared work on the a-register. I still need to figure out how to make it different from the one Ben Eater made so I'm not just copying his schematic and calling it my own. 
Minecraftchest2
started 8-bit computer ago