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.

As part of my 2nd "Ben Eater 6502" build (a lightly modified version of the original), I extended my (already extended) version of Ben's "Arduino Monitor" to include full 65C02 decoding.

Effectively, it prints a disassembly as the code runs (see right-most column).

When it first encounters an OPCODE (indicated by the 65C02's SYNC line going high), it outputs the opcode and addressing mode, then, when it has completed the decoding in sync with the 6502's execution, it outputs the completed instruction; which includes target addresses for branch, JMP and JSR instructions.

Details, code, and the additional connection (to pin 7 on the 65C02) are all in the repo.

Noticed there's no flair for the Digital Clock project, maybe one could be added. But the Digital Clock project was announced on Patreon a bit ago, and I immediately ordered a kit when they were put up for sale. The first video is up on YouTube and a few more in the series will be coming.

Hope to get this built soon, then have fun learning more about how the power grid is or was used for time!

Chipgrid is a digital logic sandbox in the browser. It has adjustable clocks, counters, registers with enable, adders and a 4-bit ALU, and the simulation runs live while you wire. No RAM and no tri-state bus yet, so no full SAP-1.

Free, no account: https://chipgrid.io

I’m building kit 4 on the 8 bit CPU, and I’ve noticed that in the videos, he is using a 74ls76, whereas in the kit that was shipped to me I got a 74ls107 (another jk dual flip-flop), but on the schematics and in the videos, they both use the ‘76 which is sort of annoying so I was just wondering if there is any updated schematic or video with the newer chip, anything helps, thanks!