I Designed Another PCB

[LonesomeLamp]

PCB = Printed Circuit Board

I decided to finally design a motherboard for my homemade computer. I got all the questions answered that I had, stuff like “how do I design it to connect to other boards?” I sat down, drew out the schematic via the appropriate program (KiCAD), assigned the footprints, laid out the traces, everything. To pay for the boards to be manufactured, I used a $50 gift card I got from my health insurance for my second Covid vaccine (and then I had an addition $5-$10 to make up with debit card lol).

The boards got approved for manufacture, the files were sent and the next day…I realized I may have made a critical mistake. I was able to check the design and the mistake had not been made, but then I noticed a little design choice I made that was less than intelligent but didn’t matter a whole lot. And then I noticed a mistake that actually does kinda matter…a lot…but the boards were already getting manufactured (and still are in production, btw).

I can fix the mistake I made easily enough. I’ll just destroy the connection that was less than smart to make and then use a wire to replace it with the connection I forgot, but we’re not done with the story yet.

I went ahead and took count of what parts I would need and started adding them to a list. A handful of LEDs, some resistors, IC sockets; mainly stuff I don't already have. And I learned my next critical mistakes. Two of the IC sockets I need either don’t exist, or cost about $10 each because they’re special purpose (have levers to clamp and release the chips). I can forgo the sockets because they only exist to allow you to replace chips after the soldering process (they also help people new to soldering because heating up the chip’s leads for too long can damage them. The sockets take place of the chips while soldering and then the chips inserted afterward).

Okay, so I have to forgo at least two of the sockets, but that’s all, right? My connector of choice to go between boards: floppy drive data cable. Can’t find those connectors either ?‍♂️. Okay, so I guess I’ll buy a few male headers. I’ll be able to use the cable still, but the board won’t have that nice rectangular guard the cable slips into.

And then I remembered a few other design choices I forgot about. I gave it a barrel jack for power (yet another part I couldn’t find) and labeled it for 5 volts. I wanted to use the connector from pc power supplies so that I could use 12 volts to power the LEDs (via transistors or driver chips) and the 5 volts for the chips. I also kinda forgot to add a reset button. Actually, I chose to add that to something else and then later realized I should have put it on the main board.

 

Anyway, remember how I said I paid around $60 total for the boards? I went with the website that does batches of five (so I’m getting five for about $10 each, including shipping). These boards are quite ambitious for me. I decided, because I had the option, to design it as a four-layer board. This means the top side has some traces, bottom side has some, and there are two more layers *inside* of the board (essentially, two two-sided circuit boards sandwiched together). And let me tell you. All four layers were desperately needed. I was down to the last three connections to make and thought I was going to have to redo about 20% of what I already had to be able to finish.

 

*EDIT*
I forgot that I was going somewhere with that last paragraph lol. The five boards costed about $60-$65 through that website, but another website was asking about $130…for three boards…

Edited February 23, 2022 by LonesomeLamp

[saltedcaramel64]

I think thats really amazing you did all that.  Good skills.

[LonesomeLamp]

UwU thank you. It actually isn’t that impressive once you know how it all works. It’s mainly just connecting lines and dots lol. You may have heard of a mobile game called…Pipes? I think? Flow? I think it was Flow. Anyway, it’s a game where you lay out colored pipes from point A to point B, you gotta take up all the spaces and your pipes can’t cross. It’s almost the exact same with PCB design. Connect A to B (and sometimes C and D and E….) and don’t cross the traces. “Filling in the squares” is done as the very last step and isn’t even required (“Filling them in” just means the copper doesn’t get removed from the surface. The actual tool in-program is called a “fill zone”).

[LonesomeLamp]

According to the website’s estimated time of completion, it should be finished by the end of today. I think the shipping I chose was 2-5 days. So uh, I’ll have the boards within a week probably. Yes, there’ll be pics of them UwU. I’ll make another version eventually where I correct that massive mistake about forgetting to rout a signal. I’ve also a few extra stuff to do too, like finding a connector I can actually get a hold of. I also got some footprint conversions to do because the through-hole version of one chip isn’t manufactured anymore whereas the surface-mount version is.

[LonesomeLamp]

I’m still waiting on DHL to get the boards over here. They’ve been on exception for a couple days at the Chinese customs place. In the meantime, I went ahead and started work on version 2. I was challenged to be mean to myself by mixing component types (ones with pins that go through the board vs ones that sit on top). I’ve some final design edits to do and one last and good look over, but it looks like a solid design. 
 

[ppdude]

13 hours ago, LonesomeLamp said:

I’m still waiting on DHL to get the boards over here. They’ve been on exception for a couple days at the Chinese customs place. In the meantime, I went ahead and started work on version 2. I was challenged to be mean to myself by mixing component types (ones with pins that go through the board vs ones that sit on top). I’ve some final design edits to do and one last and good look over, but it looks like a solid design. 
 

 

Geez!!! Do you mount/solder the components yourself or are they mounted at the factory? Once upon a time I may have tried that myself, but multiple board traces make that kind of hard to do! It sounds awfully ambitious to me. Designing that stuff ain't easy much less manufacturing it. Those prices for those boards seems pretty cheap for a low quantity run. I don't know how you do it (unless you're an electronic engineer). If I were doing it, I'd add all sorts of bells and whistles. I'm amazed at your guts.

 

[LonesomeLamp]

They’ll put the parts on the boards if requested, but they’ll only do the ones they have in stock. I would go ahead and do that, but the design uses a bunch of parts I don’t actually want (they’re stand-ins for other parts), so I’ll be doing it tediously by hand

When I did the math last night, I found that each board costs about $0.70 before tacking on the $35 engineering fee (a flat rate), which means it would be cost effective to order as many as I can afford. I think it was a bit under $40 for five and then a little over $50 for 20? The next issue is cost of parts. Talking like $60+ for one assembly and like $1000 for 20.

I almost added all the bells and whistles lol. I was adding status LEDs to the board when I decided to do all debugging stuff too. And then I realized I’d need upwards of 90 LEDs, so I went ahead and stuck to the basics lol. I can put the extra stuff on their own boards like I planned to do the IO stuff.

[Crinklz Kat]

That's actually quite nice!

Wish that kind of service was around when I dabbled in electronics!   Had to do all the work on designing the board, then make a negative of it, then using photo resist, expose it to UV light... then wash off the unexposed material, then soak/agitate it in ferric chloride for hours -- days even to etch the copper off the board everywhere except on the exposed traces.  And there was no fancy screen printing.   Or if you wanted really cheap, you could buy a pen with the etch resist compound (and hand draw the entire board) or dry erase pads and tracks if you had no access to make a photo negative of the board.  You could get that stuff at Radio Shack (and boy do I miss that store!). 

[zzyzx]

56 minutes ago, Crinklz Kat said:

You could get that stuff at Radio Shack (and boy do I miss that store!). 

@Crinklz Kat:  Are you old enough to also miss the Heathkit stores?

It's been a long time since I assembled a Heathkit H-100 computer....  <grin>

[Crinklz Kat]

59 minutes ago, zzyzx said:

@Crinklz Kat:  Are you old enough to also miss the Heathkit stores?

It's been a long time since I assembled a Heathkit H-100 computer....  <grin>

That's definitely a bit before "my time".   Though I remember the Timex-Sinclair kit advertisements.

[LonesomeLamp]

I almost tried to etch my own boards once lol. When I saw it required chemicals I could barely pronounce, I went ahead and gave up. Some of those names sounds like something a teenager can’t easily get a hold of. But yeah, options today, I’m lucky to have. Jlcpcb (the board manufacturer) gave me a coupon for one free smd production run, but they limit it to the parts they have in stock (mentioned previously) as well as only one side of the board. They also give the option to populate only two boards or the entire batch. I’m wondering what they would do for paid population. If they’ll order the parts themselves, I have a board that I *really* need them to populate for me. One component is almost as small as a grain of sand.

[LonesomeLamp]

I’ll eventually populate one board, but I’ll have to wait to buy some parts to fully populate it. The boards have light scratching across the surfaces. The scratches aren’t too easy to see. It looks like the machine that milled then dragged across the surface while moving because all boards have similar scores of the same shape, size and locations. Rubbing a finger or fingernail across the scratch feels smooth, so they must’ve happened before the solder mask was applied. The scratches are so light, that you need to hold them in the light to see them. I’d be more upset, but these are the boards that I messed up the designs of (which means I’ll be damaging them anyway to fix my errors).

[zzyzx]

@LonesomeLamp : Interesting....  The old Z80 chip is still around and in use....

[LonesomeLamp]

22 minutes ago, zzyzx said:

@LonesomeLamp : Interesting....  The old Z80 chip is still around and in use....

Not only that, but there’s even an updated version that has an internal clock generator as well as support for serial communication, as well as bringing out all unofficial instructions and features of the original chips. I believe the z80, as well as the 8080, are going to outlive any other processors. They’re already somewhere around 40 years old and still widely used in many devices. I only hear of the 8080 being used in hobby projects, but they are being manufactured still. The z80 is still used in the TI-83 as well as being the heart of many microcontrollers, and it’s easy to see why. I once read that the z80 is a little too much for anyone wanting to get into computer circuits, but I actually found it to be a perfect starting point.

[zzyzx]

1 hour ago, LonesomeLamp said:

Not only that, but there’s even an updated version that has an internal clock generator as well as support for serial communication, as well as bringing out all unofficial instructions and features of the original chips. I believe the z80, as well as the 8080, are going to outlive any other processors. They’re already somewhere around 40 years old and still widely used in many devices. I only hear of the 8080 being used in hobby projects, but they are being manufactured still. The z80 is still used in the TI-83 as well as being the heart of many microcontrollers, and it’s easy to see why. I once read that the z80 is a little too much for anyone wanting to get into computer circuits, but I actually found it to be a perfect starting point.

You're pulling me back to the Heathkit H-100 (kit version of the Zenith Z-100) computer I referenced above....  It was a dual CPU - 8085 and 8088.  The 8085 ran C/PM (85), similar to the Z80 and its predecessors.  If memory serves me correctly, the 8088 while 8 bit on the interface, was a 16 bit CPU and equivalent of the Intel 8086 that was set up with full 16 bit physical bus....  I ran MS-DOS 1, 2 and 3, on that old 8088....  Never did buy C/PM for use on the 8085....  System was an S-100 bus,  Assembly of the main board was mainly putting chips in sockets on the board.  I think it was the floppy disk controller where one had to solder (almost) all the parts on the board....  And building the associated CRT (monochrome, green or amber) monitor kit was interesting....  Kit included one very long, insulated handle nut driver and/or screw driver so you could "safely" discharge built up electric charge before working on some of the parts.....

Enjoy the fun building your device....  I don't see a lot of hobby usage at this level any more.  Heathkit and Tandy / Radio Shack stores have disappeared.  I believe even the local electronics parts store is gone (which supported local businesses).  Now need to order online or from more national mail order companies.  Of course some of the hardware engineers at work still play at this level, and I think one tech fills in boards when needed and handles patching prototype boards when wire patching is needed, etc. 

[Crinklz Kat]

Yeah, not much interest in building stuff like this - people just buy a Raspberry Pi micro controller and make it do all the work.

[zzyzx]

3 minutes ago, Crinklz Kat said:

Yeah, not much interest in building stuff like this - people just buy a Raspberry Pi micro controller and make it do all the work.

Ah, the Raspberry Pi (various forms)...  Have about three of those sitting around here to "play" with when I get the chance.....

[Crinklz Kat]

4 minutes ago, zzyzx said:

Ah, the Raspberry Pi (various forms)...  Have about three of those sitting around here to "play" with when I get the chance.....

 

[LonesomeLamp]

On 3/4/2022 at 11:16 PM, zzyzx said:

Ah, the Raspberry Pi (various forms)...  Have about three of those sitting around here to "play" with when I get the chance.....

I was going to attempt to turn one into a tablet. I got a 4” resistive touch screen to play with, but I couldn’t get the pi to play with it nicely and my coding wasn’t (isn’t) good enough to take the jab at it. And then the uSD card ended up getting used for other devices (idk where it’s at now or if it even still works).

As to my original project here, the pcb, I did a bad error with them. I didn’t bring out the memory select to the connector (intentional), nor did I bring out the IO select (not intentional). And then I was doing a final look over for the updated version and noticed a mistake with it that I also made on the old version. I didn’t connect /RD or /WR to the memory circuit ?‍♂️. Not only can it not (without modification) talk to IO devices, but it can’t even read from (or write to) its own memory bank. Thankfully, as I said, I noticed and fixed this error in the updated/fixed version of the board, which I’ve ordered (along with the parts needed to populate it).

[LonesomeLamp]

Another update:

I got the updated versions and populated one board. As far as I can tell (the wording there is important!), it’s almost perfect. Almost. There are two major issues that doesn’t really affect how well it operates, but both are still annoying to deal with. The bigger of the two, the reset circuit doesn’t work and I can’t figure out why. I can only guess that the transistor in control of it isn’t dropping enough voltage to trigger the input. The next big issue is the status LED circuit. I either didn’t pay enough attention or I misinterpreted the symbols initially, but I have the LEDs connected the wrong way to the transistors. That means the LEDs are always lit up ?‍♂️.

The other issues are mostly cosmetic. The LEDs for memory and IO reads and writes do work as intended…but I forgot how I had them laid out when I drew the silkscreen labels, and I labeled them wrong. I liked the way the labels had them more than how they were actually laid out, so I rearranged those. I made some text bigger. The connector on the board wasn’t centered, so I expanded the board slightly to make it so. The labels for the connector got hidden below the connector, so I expanded the board slightly along the other axis and scootched the text over.

It'll be a while still yet until I can attach the ROM chip to the board, but I went ahead and attached the RAM (ROM still hasn’t came back in stock). If I remember correctly, that was basically every issue I’ve had with the design so far. Though I don’t have the EEPROM yet, I should still be able to test the rest of the design by pulling the CPU off the breadboard version and then making the necessary connections to the PCB version and check that everything still behaves the same way. The RAM has been moved from the breadboard to the PCB, so really, all I need to do is check that it can access RAM. If it can, then that means the necessary connections to the memory circuit are all valid and I can move on to the next things I plan to do.

The attached pic was taken before I got the last set of LEDs, which was also before I decided to add the RAM. I was waiting to add the RAM until after I added the ROM because the RAM would get in the way of the soldering iron. I changed my mind when I found out I had mistakes to fix anyway. To be able to go ahead and populate the fixed version, I ordered some sockets to take its place. When they arrive, I can just pop one into the socket and call it done.

[LonesomeLamp]

I figured out what’s wrong with the reset circuit. Very, very, very, very small gap between transistor pin and solder pad (and solder). Once I saw that tiny gap, I took my multimeter probe and shoved it in the spot and suddenly it worked excellently. I mean, the status LED is still forever on, but at least the most crucial part actually works. Memory is still untested.

[LonesomeLamp]

The fixed versions have arrived, and I ordered a stencil for them. Now, there’s a different chip they didn’t have in stock this time around, but I do have pretty much all of the other parts I’ll need. I’m not going to today, though, because I have a ton of stuff to do on Satisfactory that I’m wanting to get out of the way. I figured I’d do the boards after I wake up tomorrow, but spend the entirety of tonight on Satisfactory (I’ll update my topic about that game in a bit lol).

In the pics, the big metal sheet is called a stencil. It sits on top of the board(s) and some solder paste gets spread across it and fills in the holes. It’s a fast way of applying solder to many pads at once. Once the paste is set and the stencil pulled off, the parts go on and then the board gets baked. The paste melts and then the board/oven goes through a cooling process. The melted paste hardens back into the solder we all know and love.

[Pre-Post Edit]
I can’t post the pics lol. I have two MB of space left on my account. I’ll figure something out. Maybe post the project to my website and then link it back here.

[Little Cub Pants]

1 hour ago, LonesomeLamp said:

The fixed versions have arrived, and I ordered a stencil for them. Now, there’s a different chip they didn’t have in stock this time around, but I do have pretty much all of the other parts I’ll need. I’m not going to today, though, because I have a ton of stuff to do on Satisfactory that I’m wanting to get out of the way. I figured I’d do the boards after I wake up tomorrow, but spend the entirety of tonight on Satisfactory (I’ll update my topic about that game in a bit lol).

In the pics, the big metal sheet is called a stencil. It sits on top of the board(s) and some solder paste gets spread across it and fills in the holes. It’s a fast way of applying solder to many pads at once. Once the paste is set and the stencil pulled off, the parts go on and then the board gets baked. The paste melts and then the board/oven goes through a cooling process. The melted paste hardens back into the solder we all know and love.

[Pre-Post Edit]
I can’t post the pics lol. I have two MB of space left on my account. I’ll figure something out. Maybe post the project to my website and then link it back here.

Big hugs buddy!♥️?♥️?☺️?♥️?? I always think that the skunk in your profile picture is taking a sip of an drink for some reason.??? LOL!?????

[LonesomeLamp]

*hugs back*
Whenever I look at it, I think he’s about to give a speech or something lmao. Like he’s adjusting his bow tie as he begins speaking into the mic. 

[Little Cub Pants]

5 minutes ago, LonesomeLamp said:

*hugs back*
Whenever I look at it, I think he’s about to give a speech or something lmao. Like he’s adjusting his bow tie as he begins speaking into the mic. 

Yeah, he ALSO looks like that too.??? LOL!???