Hi In the last video, I showed how I laid out my rev A uh power supply board and what went into that? well I said I'd do another video showing you how I uh laid out the revb revision of the board in this case uh took the existing rev a board I've got here as you saw last time and uh, basically, uh changed it a little bit. added a few components on here for revb and it doesn't look like there's a huge amount of difference. there's rev A it's uh, down in the bottom right corner here. there's not too many Uh components for example.

and I've added those I Squar sea chips over here and it's a little quite a bit. uh, more dense uh layout in terms of component, uh, density and things like that. So, but there weren't a huge number of changes, but uh, surprisingly. um, as you might find out, it does actually take a almost the same amount of effort really to uh, make uh, some small changes to an existing board as it does to lay out an existing board from scratch.

That's not always the case, but in this case it, it probably wasn't. uh, too far off. So uh, what I'll do is I played back the existing rev one at time 10 speed uh I didn't want to make this video as long as the last one so I'll do this as a times 20 speed so you can figure out how long I did based on the uh amount of time uh multiplied by 20. Let's start out by having a look at the schematic here and here's the existing one: um I've shown this before I squeezed it all onto the one A4 uh page and it looks uh, quite dense.

but I was I was happy that it was all on one page. so I did keep it all on one page for revb. but I actually modulized the thing and changed it to an A3 size sheet like this. and of course I added these uh I squ C uh chips down here.

they're to 18 pin dip package so they're fairly um, you know, large devices to fit onto an existing populated Uh board. It's not like they little surface mount jobs or something like that. um what? I expanded the LCD connector down here with the RGB lead interface I uh increased the um the serial uh header IO to make it ftdi uh compatible. so I increased uh the number of pins on there to break out the things I added another serial um IO connector for um, well, not serial IO sorry, uh, that's labeled incorrectly but another IO connector for the Uh switch um IO chip down here just in case you wanted to add like a keypad interface or something like that and uh, that was that was really the main Uh change.

Of course there were a couple of Uh things around the Um AVR microcontroller like the Uh like the 8 MHz resonator here and a couple of pinch changes and and stuff like that. a few a an ARF change and a reset pin change and a couple of other things but so not a huge amount of difference really. uh compared to the two uh, the two schematics here, the uh LED of course, um on the reset pin. that was one of the things that we talked about changing.

So one of the first things you want to do once you've got when you want to update a board like this. Once you've done your uh, your new schematic like this and you got your Footprints attached to each component, you know. So if I double click on that component, it pops up and and it's the correct package I want dip 18 and uh, all that sort of stuff then what you do is you push this information through to the schematic and I won't you know I won't tell you how to use Alum designer here to actually do that, but um, it's actually off the screen capture here, you can't see it, but it's update PCB document and when you push through all of these uh, changes to an existing board, then what you end up with is a board with uh, what you end up with is your rev a PCB like this, but it'll have all of your additional components over on one side here. at least that's how Altium does it.

Other packages will vary, but anyway, so you import all of your extra components, you'll end up with a whole bunch of components over here with all the rats nests going, uh, over all the net connections going over and you've got to rip up your existing design or try and put them fit it onto your existing rev a board. So let's actually try and do that. Live here. What I'm going to do is I'm going to push through my new revb schematic Uh, I'm going to push that through to my rev A PCB and update component links Yes, yes, and continue and bang.

It's going to execute. It's going to make all these changes here. all these nets. It's going to add in all these components, all that sort of stuff.

so let's execute all that it goes through. This is just an out him designer specific thing. There might be a few errors in here if you haven't got Footprints correct and stuff like that. but generally what you're going to end up with is Bingo.

Here it is. You're going to end up with this in in this case, it's actually a room Alum Designer Um, it puts it in a room for you I don't like that. So what we've got is we've got these two 18 pin uh I Squ C uh interface dip chips. We've got the new uh serial connector up here or it's actually replaced it.

Um, you'll notice that down in here. The LCD LCD connector down in there has now got these three extra pins there. one two three and you see they're overlapping. so it it took that existing uh, eight pin or seven pin connector or whatever it was and added three extra pins and you can see that they're conflicting in with the existing uh Vas there and tracers and ground plane underneath and things like that.

So um, that's what happens if you change your footprint. And likewise, the serial connector over here which was only a five, uh, way one uh down here or thereabouts, it's it's added the extra pins on there so we're going to have to end up uh, moving that and I'm not going to um, clearly. uh, do that now because I've already, uh, done that and I'll play that back. I'll play back all these edits at uh, times 20 speed so you can see just how much work is involved in shuffling things because you know you've got to fit all of these components here onto Somehow you know down in here.

I've got to get these dip packages down in here like this: I've got to somehow get a serial connector on the board. you'll see in the final layout that I end up adding it around about up here somewhere and uh, there's another connector down here. there's and all these resistors around here and and it you know it's It looks a bit daunting when you first actually. uh, do it and well.

and and it, pretty much is. And that's why it takes a lot of little edits and shuffling tracks here and there and ripping things up and moving and retrying stuff and finding out that oh, the last component just didn't fit and then I'm going to have to move this whole section over and then it all gets, uh, quite complicated. So that's why an edit of an existing board. even a fairly simple edit I mean there's not that many components we're trying to add here.

There's two chips, a couple of connectors, and a, you know, a dozen dozen resistors or so. But yeah, it can take almost as long as the existing board you'll find. It's actually quite remarkable how long it can actually take. and uh, once again, that depends on the complexity of the board.

Some it won't matter, you know it'll be very quick and easy, others will take could take five times longer than the original. Uh. layout could be really bad. You might have to rip up the whole thing, but as you'll see hopefully in this uh, time lapse video, that uh, I won't make too many changes like the main.

um, the main AVR microcontroller here I I don't actually, uh, end up moving that I don't think maybe I shuffle it a you know, a couple of millimeters here or there or something like that I don't actually remember, but you'll find that a good lot of it is still in its existing location. but of course, um, some of this silk screen. I've got a move that sort of stuff. the Platypus is probably going to move and uh, all sorts of things.

One of the first things you're going to want to do uh is get rid of that ground plane because it's going to be a pain in the butt now. I Now you don't actually go and actually delete the ground plane. So what you can do is just go in there and you can actually uh uh, hide. If you go into polygon actions, you can actually shove all of the polygon.

so Bang! I've now got all the bottom layer available for Um for all of my Uh routing and things like that, so nothing conflicts. and you'll find that if I go in and do a design rule check now there'll be probably you know there could be dozens or hundreds of errors or something like that because all things are shorted out and not connected and various things. But as you can see all of those Uh nets, all of those rats Nets those fromt as they're called in the atium world, they're um, they're all the unrouted connections so we've still got to make all all of those all of those connections. So we'll go through the uh times.

20 time lapse now. Um, unfortunately the first part of the time lapse was was actually corrupted somehow so I didn't actually capture that. So you, um, it'll start actually partway through the process where I I believe I have a couple of the Uh chips down in here and I've already shuffled a few things around. so sorry about that.

but uh, after that I think I captured most of it. So I'll add some commentary on top of the times. 20 time lapse? Let's go and here we go. As you can see I've got, um, already a bunch of resistors there in place.

uh, they're the pull-up resistors I believe for the uh I squar c um chip which doesn't actually need um, because it's got internal, uh, active active software pull-ups You can Define within the chip. but anyway, I thought I'd add some external ones in there I might remove them on the next version perhaps. Uh, cuz they do take up some room. But anyway, let's take a look.

I'm trying to shuffle in the chip there and you'll notice that right next to it I'm I'm I'm now dragging it out and dragging it around trying to figure out the best orientation for it and how it's going to work out. It's going to wire into the other parts of it and I've decided to, actually, um, move that. oh no, there we go. I moved it back and I've looks like I've settled on that orientation at least for now I've dragged in the other chip I'm check checking something on the schematic there, mucking around with a bypass cap there and you'll notice that I've got the connector the expansion connector right next to the chip because that's where it should be because you wire it if you actually look at that little um circuit.

IT wires Um for that. for those pull-up resistors in that expansion connector, they're right next to each other, so it makes sense to put it right there. It doesn't make sense to put it on the edge of the board or somewhere else. It's silly you'd have to wire eight tracers right across.

But anyway, now I'm uh McKing around with uh, the odd resistor up the top there moving some tracers not sure putting in a vaa there, jumping through to the bottom layer because I couldn't get around. so I'm um uh, there's a uh, a T92 pack is there I'm Shuffling around I'm moving a few things up here I'm not exactly uh sure why I was doing that I'm I'm obviously trying to gain room. Anything that I move within, Uh, doing this board? Um, you'll have to forgive me. It's been a couple of weeks since since I've actually, uh laid this thing out.

Uh, now I'm doing the commentary. so I've got to remember what I actually did. I'm playing around with the schematic checking something I've got another. um I've got the bunch of uh 10.

I've got another bunch of 10 resistors there and I'm uh, I've put those in somewhere but I haven't uh been too concerned with those I lost interest in that and decided to go onto something else now. I'm it looks like I'm tackling the Um getting room for the serial connector so you'll notice that I'm uh around the AVR chip here this is going quite fast. This is hard to do, but I've pretty much decided I think at this point that I'm going to put that uh serial expansion connector right next to the chip because it makes sense because most of the Um signals uh, not only duplicated from that um, uh in circuit programming connector that I've got next to the chip there the AVR that's labeled Avrisp so it makes sense to put the connector whereas before I had it in the top left, uh corner. but I I decided that uh, that I really had to compromise there and I just put it smack in the middle of the board right next to the chip because getting um, those 10 traces all the way over to the other side of the board.

it would have required me to rip up a whole ton of stuff probably half the layout on in that top, uh, left corner or most of it, it would have been really ugly. So I've decided to put um, the serial connector which I'll move it in there later, but I think I'm just uh making room for that now I'm putting in a couple of other uh, looks like I'm Shuffling my uh, this is my microcurrent part of the circuit I changed the odd resistor there. um, so there were a few missing resistors there and I've decided to shuffle that over because I need to get those multiple traces you can see like running sort of like a bus there I need to get uh, those through and I know I'm going to need some more room in there as well. So I'm uh, ripping up that sort of stuff I rerouted the power there for the microcurrent uh Maxum chip and I'm playing around with that bus there, deciding because the pinouts on my Chip have changed by the way, my AVR microcontroller.

So I'm trying to, actually, uh, trying to, uh, get the Trac on, probably have to rip up half the tracers to the microcontroller and then rewire them straight through like that. and that's what I'm trying to do. put in a few more resistors there, uh, dragged them in I've decided no I want to shuffle them over to the left of those couple of pins. so unless I actually uh was commentating while laying out this video.

it's hard to explain exactly what I'm thinking at this point because I'm taking into account a whole bunch of net connections and things like that and where they go and I can see them. you might not be able to, uh, see them there, but I I've got the schematic in my head and I've also got the uh The Rat's Nest lines there of where things going to go and I'm building up a map of all this um stuff in my head pretty almost subconscious. L uh kind of thing. So I I I Kind of know that I'm going to need at least another two traces through there or through these two pins.

so I better move those couple of resistors over. and things like that, so looks like I just highlighted the power net there. so I was obviously playing around with that um and I looks like I'm freeing up more room there for the serial lines. here we go.

I just dragged all those back I've got uh I dragged in another capacitor there. That's all that's part of the reset circuit. I think that changed between the two revisions. So actually I'm yeah.

I'm going to have to move a lot more stuff in there to put in that serial connector. I'm mucking around with a few of the um, really, just slightly tweaking the locations of those Um switches. I'm not sure why I did that. Um, probably I'm just freeing up a few.

just a little bit of space here and there. a few few millimeters things like that. um, oh, that's right. I think they were placed on a different Uh grid.

so I probably um, uh, redid them on a metric Grid or something like that perhaps. So uh, once again, I'm probably using like a 50 th Uh grid here or a 25 th uh routing grid with a 50 th Uh component or a half a millimeter component. uh move grid. so the component grid will be in Uh will actually be in Metric and the routing grid will be in Uh Imperial be 50 or 25 th.

might switch to between those depending on the work down there and here. I am back at the Iqu C chip and if you can see the the Um serial, expand the Um this Uh switch expansion connector in there that 10 pin connector. It takes up no room at all because those Uh traces go directly from the I Squar C chip right up uh, through the resistors through the connector and it's it's all very efficient down there around that I Squar C chip I Really like that. so if you're not fussy about where expansion connector goes, you can really save a lot of PCB space and there we go.

I'm now I'm moving in my serial connector. Here it comes I've uh, looks like I've shuffled up a few of the looks like I've shuffled up that uh back, uh, that protection uh diode there and I'm playing around with a few with the space up there and it's getting quite tight. There we go I've moved, moved the diodes again, the TVs there and I'm Shuffling oh there we go bang. I've got room for my serial expansion connector right next to the Chip Magic I've shuffled in I'm not sure how long I am into the process now, but there you go.

I'm rerouting a few of those tracers there just so I can eliminate using any Uh vas at all. I can wire those straight through and you can see how short some of those traces were. You got a glimpse of that going directly from the Avrisp connector through to the Micro, through to the Um Cn3, there, the Io expansion connector. and if you had that expansion connector right on the other side of the board as I did before, then you would have to Route all those tracers from one side to the other and on a double-sided layout like this, that could completely ruin your entire design, it'd be horrible and you'd have no ground plane on the bottom be all ripped up or you'd have to restart the design from scratch.

But now I'm left with all these traces there which I've got to cut back I've got to rip those up and uh, um, think about how to reroute those uh, through the best, uh, through the best way to get those back to the microcontroller cuz the pinouts uh from my microcontroller have all changed. so I've got to rip them up and then, uh, figure out the best routing scheme to get back to them there and this is going quite fast. And as you can see, I'm jumping back and forth between my schematic uh, a lot and that happens. I might even change a few Nets there.

Um, I may have even, uh, pushed yeah, I think yes, I did there you go I pushed through a uh change from my schematic through to my PCB because I thought that uh, that would give me an easier uh routing pass. So I swapped a couple of pins and that's pin swapping. You can do that using back annotation techniques uh, depending on how your software works with that, but you can actually make changes in the PCB and then what's called back annotate that into your schematic so it'll automatically make schematic changes. I'm that works um, sometimes.

but I'm I'm a fan if it's just a simple edit like I'm just swapping two pins on a simple design like this I won't use the back annotation feature. I'll just change it on the schematic and then forward forward annotation, push it through to the Um through to the PCB. There we go. I couldn't get those two tracers through I had to shuffle the power uh Trace up there.

but I'm dragging those two traces at a time. Somebody asked that in the last video what I'm doing there. they aren't a differential pair. I'm just actually highlighting and dragging, but both traces at a time because I know they going to the same side of the board.

so I may as well drag them um at the same time and keep them together and the software handles are spacing for that. So there would have been 10 thou uh space to meet my Um 10 10 uh rules and everything works fine. So I'm back down to my Uh I Squar C devices down here and I'm Shuffling a few traces there back and forth figuring out the best route and uh, there you go, that's um and who I'm back up to the oh, there we go I've decided I need more room. Just moved my platypus there, shuffled the serial connector again I decided I needed it down one I'm not sure the reason for that.

ah I need more traces out of there? There you go. I needed a third Trace to go from the bottom right corner of the board to the top left part of the board. so instead of doing that on the bottom, which would cut through all of your uh, ground plane, that would be ridiculous I decided to shuffle um couple of power tracks and those diodes those big dodes up the top gain an extra room for that one. Trace Um, it's a fair bit of work just to add.

when you get to the end of the layout, you might find oh I've got to get one Trace left from one side of the board to the other and then you might have to move 10 components. you might have to shuffle uh, 10 components by. you know, 50 TH or something like that to get from one side of the board to the other and it can be crazy. So uh, those? oh there we go.

I'm Maring Oh, looks like I've done most of it I'm mucking around with some silk screen now. looks like my routing is pretty much finished I see a few resistors down the bottom, but uh, no, there we go. I still got some tracers I Maybe I was a bit bored there with the uh, uh, routing the tracers. so I decided to do some uh therapy and go and move some of the silk screen for a while just to clear my head.

perhaps? uh, that happens, you can. It's a complex process. There's one hell of a snaking Trace that went from the bottom, right, bottom, right corner of the board, right around through to the micro and I ended up having to use a VR. So I'm really getting down to the nasty end of it now.

where um, if you've got any traces left that need to go any significant distances, it can be a real real pain in the butt. and those four resistors down the bottom. They're um for the USB connector. so I'm thinking I'm leaving those because they're not important.

They're not, um, electrically important or anything like that because they they're just setting the DC level on the uh USB port. So I figured I'd put those in last and if push came to shove, I could even possibly leave those off. If I was absolutely desperate for room, if I had to leave some components off this board, it would probably be those USB those resistors for the USB connector. um, cuz they're not essential, it's just a nicity.

So uh, in effect I'm um, hedging my bet here that if I do run out of room, ah well, I can drop a feat Fe It's Not Unusual to actually uh, do that on a project like this where I'm changing my mind all the time with things so it doesn't you know it's not a huge deal if I figure out oh, I don't have the space I'll just drop that feature or I'll change that feature or modify it or something like that. So um, here we go: I'm trying to get a trace right around the bottom edge of the board there so it looks like I shuffled up those switches just a just a tiny Tad to get room for that second Trace around the bottom. perhaps working on my Power Trace again there. and where are we up to now? Looks like we're still McKing around with the I Squar C stuff down in I'm back on my microcurrent.

here we go: I don't think I've finished my microcurrent and yeah, a few the Oddball resistor around there. Um, these I haven't finished the connection for these resistors. I've shuffled part of the um part of the microcurrent circuit around there and I've got the odd Trace left and I from memory. it starting to get a little bit frustrating Now I've got a couple of odd ball ones left and it's getting quite tight and and it's getting annoying now.

I'm thinking about my USB resistors. There we go. they just squeezing there with a little bit of silk screen overlap. Oh well, you can't have everything.

so um, maybe I shuffle tidy that up later. The last thing I'm worried about is a little bit of Um silk screen over silk screen. That's no big deal at all for a board like this and I thought I was up to my LCD connector here, but uh, the RGB um extra pins but I've already done those I must have missed those somewhere within all this times. 20 speed.

This is phenomenal trying to keep up with this, but uh, I think we're always done. Oh look, there's a yeah little pain in the butt trying to figure out the best way to route a few traces there. I Ripped up, retried, tried to VI tried to eliminate any Uh Vs and traces on the the underside if I can things like that, even if the tracers have to go snaking around the board. Um, when you're down to the last couple because generally when you're laying out uh, a board like this, you try and keep the Trac as the minimal length.

That's the key. It's only at the end where you're so desperate to get uh, you know, traces um that are finished. That's why you want to try and mount things, route things as a modular type thing as I explained in the last video. um now big as then you can keep all the module things and then you only have to join power and a few data connections usually between the modules depends on your design of course, but um, looks like I've still got a few traces up there I've got uh some bypass caps up the top I'm R trying to route my five volt power around down to the bottom resistors.

I've I Mass moved a few of those resistors just to get a uh, shuffled them over a bit just to get my 5V power around. Now this can be tricky because I've look I had to snake that five I had to um, make that 5V I had to neck down what what's called neck down the 5V uh Power Trace I probably used like 100 th width and I had to neck down to 80 or thin it down to try and get under those uh uh pots at the bottom. uh because those pots have to be a certain distance from the edge of the board so I don't have much leveraging uh much uh uh. spare room in moving those.

So I had to neck down the power but I used 100 th most of the way and looks like I'm trying to I'm rotating my platypus a few times. you know, takes a bit a while to work out the best location for the Platypus but looks like it was the same as last time. Just shuffled over a bit mucking around with the silk screen and jeez. I think we're almost done? I'm looking for my micro Supply There there we go.

I Think we're done. We're going to do a DRC check There we go. There's our DRC and uh, looks like we've got a few errors. tidying those up.

Looks like just a few clearance errors. Probably doesn't meet the 10th hour clearance. It looks like I'm Shuffling I changed my ground plane there I'm changing my polygon. it's part of the ground plane I've just decided to shuffle that there cuz there probably wasn't enough room there to get the uh.

the polygon was a bit thin there, even though on the left hand side, even though it didn't carry any significant current on the left hand side. Um, just as good practice I Decided to and there we go. Oh, you missed it. I Just joined the polygon at the star Point down in the bottom left corner and now I'm marking around.

I'm in the whole size editor now so I'm just tidying up a few. uh I think I'm in The whole size editor there. I'm just uh, checking a few things and boom, that's it. Is that it? That's all we got.

It's all over. So there you go. there's our completed board. and yeah, that took probably, um, not as long as the original layout, but uh, not that far off it and there a lot more uh, involved in there a lot of thinking.

A lot of rip up retry for a lot of things. and but as you can see, I didn't rip up and retry a lot of components. So just the act that you've got to do a dozen or so components, even on a fairly simple, rudimentary double-sided design like this, can take a fair amount of time. So there you go.

I Hope you given that's giv you a bit of insight into, uh, not just laying out a board from scratch, but actually making changes to an existing board. I'll catch you next time.