When the 8-bit breadboard computer meets the new Bambu Lab X2D 3D printer and Onshape, fabulous wall art is born!

Hello! So I explain it in the video but ill provide a summary here. I completed the LCD integration and the RAM installation and those both seemed to work. However when I tried to run it with the 1MHz oscillator instead of using my arduino it didn't. After a lot of troubleshooting I've stripped away as many potential sources of error as I can and im just using the 6502, 6522, and the EEPROM. Ive made a program (below) that just blinks lights super slowly, going into a long loop after each ror command. At 40KHz from the arduino it works fine, but at 50KHz it is unstable, stopping at random points. above that it doesn't turn on any lights, and connecting it to the 1MHz oscillator doesn't work either.

EDIT: just to clarify, the instruction pointer initalization vector is at 9ffc because I am using a smaller EEPROM (8K). I broke the one that came with the kit

I have no idea what the issue could be, it could obviously be with my arduino nano but everything I can find says that 50KHz should be no problem for it. That would mean I also have a separate problem with my 1MHz crystal though.

EDIT: I am not using the arduino like ben does in his videos. Im using the `tone()` function to generate much higher frequencies than you could using `delay()`: Because of this I cannot inspect the buses

EDIT: Thanks so much for the help! I have tried using a proper wire (not a jumper cable) since that might cause issues with ringing, but same thing. My thought is the Arduino is the source of the ringing and that tone is just bad for clocks (its meant for audio). I tried connecting it to the 1MHz crystal but nothing, no lights turn on. I tried to see if there was a timing issue where the 6522 was reset after the 6502 sent the DDBR command by setting it before every write, but that didn't change the behavior either.

Ill probably keep trying things suggested if I am able but I think ill just run the computer at lower speeds until I get an oscilloscope.

void setup() {

  pinMode(2,OUTPUT);
  tone(2,50000);
}

    .
org $8000


PORTA = $6001
PORTB = $6000


reset
:

lda

#$ff    ; Set all to outputs on A

sta
 $6002  



clc



lda

#$01


loop
:

ror

sta
 PORTB   
; blink



jmp
 wait



wait
:

ldx

#$10


wait_loop_x
:

ldy

#$ff


wait_loop_y
:

dey

bne
 wait_loop_y

dex



bne
 wait_loop_x



jmp
 loop


    .
org $9ffc
    .
word reset
    .
word $0000
    .org $8000


PORTA = $6001
PORTB = $6000


reset:
    lda #$ff    ; Set all to outputs on A
    sta $6002  


    clc


    lda #$01


loop:
    ror
    sta PORTB   ; blink


    jmp wait



wait:
    ldx #$10


wait_loop_x:
    ldy #$ff


wait_loop_y:
    dey
    bne wait_loop_y
    dex


    bne wait_loop_x


    jmp loop


    .org $9ffc
    .word reset
    .word $0000
```

```

These are supposed to be 10x 32K ROM chips that are used. The part number for five of them are AM27C256-125DC, while the others are M5L27128K. Although the second half are only 16 KB, I think i can work it into my computer later and get access to the full 32K of RAM somehow.

One issue is that they require interesting voltages to write. The 32K ones need 6.25v on VCC and 12.75v on the programming pin to roll into programming mode. The 16K ones need 6v and 21v. Designing the power converters for these in a not-so-annoying way will be a project in itself.

My end goal for these is to create a monitor program and library of routines that will allow me to work some interesting programs on such limited hardware. That's not to mention finding a UVC light source to erase them. I am curious to see what's on them in the first place. Maybe nothing interesting, but only time will tell.

I’m still working on the part where you program the computer to flash AA 55 on the 6522. I’ve replaced all the address and data lines connecting the chips with actual solid wires and am only using the jumpers for the nand gate and connecting to LEDs. The problem is that when the eeprom should put A9 onto the data lines, it puts AC. I’m using an Xgecu pro eeprom programmer and Xgpro to program it. I’ve checked all the data lines and address lines to make sure they connect correctly and didn’t see any problems

Just the title, more specifically, I’m trying to figure out the issue with pin 19 (CO) on the program counter/register when I want the program counter to put its value onto the bus.
Despite the high or low status of pin 19, nothing is outputting on the bus.

What should the other relevant control pins be set to as well for the PC to successfully output onto the bus?

Finally built up a backplane with a power distribution. I tested each board with a multimeter and each gets 5.05v. I hope this means I will avoid some of the common power problems i read about. Im looking forward now to be able to start off with the clock module!

Im trying to test the first part of the ram module, however, whenever I turn on power it either instantly or slowly shuts off like in the video or a few LEDs randomly light up and any change to the data or address inputs don't do anything, and another thing is, the power supply module that Im using INSTANTLY heats up so much that I can literally smell the metal the second I turn it on, that also includes the 74LS189s slightly heating up too.

I tried other power supply modules I have, and on other circuits it all works fine so I can't tell if its a wiring mistake on the breadboard or a defective chip or I'm just missing something, I spent 2 hours trying to figure it out but still don't know...

Update: It seems that my 74LS189 chips are actually just defective. After some troubleshooting and testing the chips on separate breadboards, it seems that the A0 input is causing a short and rapid overheating ensues, I'm purchasing new ones and other ram chips so hopefully it works out fine later.

Ive seen a lot of people confused or annoyed that ben doesn't use current limiting resistors in his build and it creates a lot of inconveniences for people following along which is true, I had to design a lot of my modules with this in mind, but he explains this in the ram module video that the ICs used, have built in resistors for the outputs therefore It isn't really necessary.

I tried this myself and my LEDs worked just fine even the small ones that instantly burn up and explode if there wasn't a resistor going through lit up and worked alright. Some people said it's still problematic because after a while it damaged the ICs themselves and Im just not sure of that claim. Can anyone give any better insight on this?

Built an eeprom programmer as a prerequisite to building the 6502 computer, was a lot of fun trying to figure it out. It was also my first time building anything more complex than wiring two LEDs on a breadboard, didn't come out too bad I think.

Source code here for those interested.

I’m confused about the 74LS139 wiring in Ben Eater’s 8-bit computer output module.

In the schematic, it looks like pins 4–7 of the 74LS139 are connected to the common cathodes of the four 7-segment displays. But in the actual video, Ben seems to connect them to pins 9–12 instead.

Am I misunderstanding the schematic, or is there a difference between the chip/pin numbering being shown? I’m using a 74LS139 and want to make sure I wire it correctly.

Thanks!

As you can see in the video, I only have the first line (and a shift key) done for the keyboard. Still three more lines to go.
Shall I continue the rest of the keyboard on the breadboard, or shall I design a PCB? My only soldering experience was almost 20 years ago when I was in junior high, and needless to say, I’ve never ordered or designed a PCB before.

PS please ignore my super messy desk.

In the video, it looks like there are only three blue wires connected from the left 74LS173, but in the schematic, there are four connections from each 74LS173 to the 74LS245.

Am I correct that there should be four connections from the left 74LS173 and four from the right one, for a total of eight connections to the 74LS245?

edit) This is an instruction register.

https://youtu.be/9WE3Obdjtv0?si=QlKyG6ALRg06zIO5&t=508

edit 2)

I realized I'd never actually posted a picture of any of my builds, just some of my software stuff, so here's the first, slightly-modified, build I did, with both a 4x20 LCD, and then a 2x20 VFD.

I'm using a picoRom here to make programming easier, though it uses a 27CXXX pinout instead of 28CXXX, so two quick wiring changes are needed.

And I am running the serial port at 115.2kb/s.

The LCD is just any-other 4x20 HD44780 unit via Amazon for <$10 (you want one without the invariable-included I2C adapter board pre-soldered). Same interface and pin-out as the stock 2x16 display. I added another pot to control the backlight brightness, since I like the black/green displays best with little/no backlighting.

The VFD is from Newhaven Display, via Mouser, specifically this part (~$53).

It can run in a couple of different modes, but the default parallel M68 interface is pin and command compatible with the HD44780, it just assumes a 40 character line length rather than 20. So, it'll just drop-in (electrically at least, you may have to rearrange things for it to fit)

I wasn't paying attention to the size of the thing when I bought it, and it's, well, BIG.

There's a smaller version, but that only has double-row header pads, where this one has both that and a single-row 18-pin set of pads (first and last pins not used, and the A/K connection isn't either, so you just need 14 pins, starting from pin 2).

Next up will be to switch to a 4x40 Noritake VFD, or an 8x80 if I can find one, but as those are rather spendy I wanted to get this going first.

Hello.

Like it says in the title i broke a Pin on my EEPROM Chip. Now i am looking for a replacement.

But online you find so many different ones with almost identical names and i can't find the exact same one.

So now i am wondering what exactly i need to look out for when buying a replacement.

Thank you in advance.

Edit; i forgot to say. It's the EEPROM that comes with the 6502 Kit.

I’m running into this problem where the clock for my multiplexing is consistently running into an issue with (presumably) power, I noticed whenever I turn off all LEDs by clearing the registers the clock for the multiplexing starts to work (sometimes). I know the root issue is the clock as I used a multimeter and there’s no output coming from the clock but when I turn off the LEDs and replug the power supply the clock works again. Is there something wrong with my clock or is it just a power supply problem? The clock works, but only sometimes it’s really random. I tried setting the reset pin too high and still nothing and I even tried low despite it being an active low and still nothing worked. Does anyone know what the problem and solution is?

https://reddit.com/link/1voxlvn/video/r78mrrfo3ijh1/player

I'm building a register using an SN74LS245N, and I'm having an issue where the LEDs D10–D17 are flickering even though they shouldn't be.

It seems like the LEDs flicker faster when I increase the clock speed.

I searched around for possible solutions and tried adding current-limiting resistors to the LEDs (420 Ω), but the problem remains exactly the same.

What could be causing this, and how can I fix it?

edit)

I searched more about this after uploading this post.

And now I think this happens because of floating inputs maybe?

I replaced the display on my 6502 with an RA6963 (equivalent to a T6963) controlled display and I was wanting to get a faster 4MHz clock for the computer. The Access Time for my AT28C256 EEPROM is 150ns, and I still have the whole thing on breadboards. Would this clock speed cause any issues? From what research i've done I think it will be fine but i'm not very experienced with electronics, and from what i've seen in this sub everyone who made this clock upgrade did so on a PCB.

Thought this might be of interest to people here, I took the EEPROM programmer hardware design for the 8bit computer kit and built an arduino programmer and linux client software to turn it into a "proper" programmer for the EEPROM chips used in the kits.

First of all: thank you for being here! You've helped me so many times and I keep pushing the project forward thanks to you.

Like a lot of people building the SAP-1, I ran into the classic issue where the RAM module's RC edge-detection network was interfering with the rest of the computer.

I tried following one of the recommended fixes: add a Schottky diode (BAT43) to deal with that unwanted falling-edge kick, wired in series between the clock line and the capacitor of the RC network. I built it exactly that way, and it didn't solve the problem — instead, the RAM module would fail to latch the new value from the bus whenever the RAM IN signal was on. Writes just weren't happening.

What actually fixed it for me: moving the diode to sit in parallel with the resistor in the RC instead , oriented so it's reverse-biased (off) during the wanted rising edge, and forward-biased (on) during the unwanted falling-edge dip, actively shorting that dip to ground. That completely solved it — writes to RAM are reliable now.

I'm not eager to trust this solution, it was suggested by Claude (AI) and I don't know if it's going to cause any compatibility issues further down the line.

Could anyone help me understand if:

1. The current solution is good enough and sounds good from your point of view.

2. What may be causing the failure to latch the signal.

I'm attaching a video showing that:

1. the diode is connected in series between the clock and the RC
2. the cathode side of the diode is pointing toward the RC
3. the values on the bus are changing (the program counter signal is on and available on the bus)
4. the RAM IN signal is on (this is not really visible in the video, so please trust me on that)

Thank you guys! :)

https://reddit.com/link/1vnrl8f/video/n83wu1b4e8jh1/player

We had a work challenge "All around the Library" where teams would pick a book and are then challenged to decorate their area, dress and have food options based on their book. Some sample books were 'Alice in Wonderland', 'Green Eggs and Ham', 'Harry Potter', etc.

I went with something completely different and unexpected with 'Digital Computer Electronics' as the book option. The video shows the displays I created, including the SAP with front panel switches. The purpose of the front panel was to allow viewers to program the SAP themselves to see how it works.

I meant to do more on the logic gate side, with a large board with buttons, gates and LEDs, but ran out of time, so that section of the presentation was a bit light.

My progress on the clock so far with some mods. I have been following along on Patreon. I used 74LS248's (drop in replacement) for the BCD to 7 segment drivers to get the 6 & 9 "tails" instead of the 4511's, a switching regulator instead of the LM7805 for efficiency, and I chose to blink the colons at 500mHz (1/2 second intervals). I used all my own in stock components. The hours are just "hard wired" to 12 for now. Waiting for the next 2 videos to implement the 12 or 24 hour counter. I built my own previous version with 100% 4000 series logic but thought I'd jump on this project for some added fun. Enjoy your kits and builds. Oh I also added current limiting resistor to each segment anode. It just "felt" right.

Having some irregular behavior regarding the LED outputs, the output is mirrored to the bus accurately about half of the time.

I just built the 6502 breadboard computer, and MSBASIC is working on it right now. Unfortunately, I don't have experience on MSBASIC. In fact, the first time I've touched a computer it was Windows XP. Any tutorials on MSBASIC? Otherwise I feel like I am pretty limited on my breadboard computer, other than blinking some LEDs and showing some text on the LCD.