Hi Welcome to the second part in the USB Power Supply Design series. And this time I'm going to start out by talking about the case for this thing and the selection of the case and the form factor and stuff like that because I think it's very important uh for a lot of projects. In fact, it's absolutely essential for a lot of products to start out with how it's going to look and feel and what case you're going to build into it, what the user interface is going to be like, and your physical requirements like that cuz that can determine uh often your uh electrical requirements as well. You know, if it's a tiny case and you got a power supply, well, you're going to be limited to how much uh, heat dissipation for example, you can put into it, or what type of connectors.

How many output connectors can you fit a whole bunch? What input connectors can you have all that sort of thing? So my requirement for this uh, USB power supply when I first came up with the uh idea for it I I had just done the uh microcurrent, the first version of the microcurrent and you've uh, seen that before and um, so this was about in 2009 or thereabouts and uh, I had used the um Australian-made Jiffy Box made in Western Australia here by Um Altronics and I really like those uh cases. They're very cheap and of course they're made in Australia I Wanted to keep local content as much as possible so I wanted my a little USB uh power supply for my own uh use I Thought it'd be quite nice. so I naturally just uh built it into um, the same case because I was already getting the board made so on the same panel I could get uh, these prototype boards made as well. so it made sense.

That's why it's red, that's why it fits into the same box. It was just a no-brainer I Just quickly lashed it together at the time, but as you can see, it's really not that suited for I think it's one of its intended purposes, that it needs to be really small so that you can say throw it in your very thin the outer pocket on your notebook uh uh case for example and this doesn't really cut it. You've got the huge binding post protuding up here. you've got big displays perued in there, and the case itself is thick.

and of course most of the room in there is actually um, uh, taken up by it's just, you know, it's just space in there. nothing at all. just The Binding post protruding from the bottom. so that's a pretty inefficient design as far as space utilization.

you know, three-dimensional utilization of the space. It's very poor. So um I didn't really think about it much more when I designed the uh second one here I just decided to go for the knobs instead of the Uh buttons here and uh smaller displays and uh, but and I decided to mount The Binding post on the end of the case. so this was designed to sit in here.

it's got all the CC Tre on the back and this is designed to sit in here like this and I was going to just I thought I'd just put the binding post protruding from the back there because you really few people have asked uh in the comments for the previous one. oh, use spring terminals or 4 mm uh, banana low PR 4 mm banana Jacks But really, for a power supply I Think it's absolutely essential to have a 4 mm binding post. um and and these are dirt cheap available anywhere in industry standard stuff. So I'm going to base it on this.

So this was an absolute musthave requirement in my USB power supply. and it's a matter of well, how do I mount these things? By the way, I Know somebody posted a link for smaller profile ones about that long or something like that that you can get from um, uh, nework SL Fels or something like that, but they're more expensive. uh, bit more obscure I don't know. I'm going to design mine around these industry standard 4mm binding post.

So how do I Mount this? Well, it makes sense because I want this to be as thin and as small as possible I want it to Mount into that notebook case so obviously makes sense to mount them on the end like this. Um, and that's what I did for this second version of the micro Supply here. but it still had the big knobs because I was obsessed with having knobs on this thing and well, it's just. you know, they just protrude and you can't slide in the case nicely.

Knobs great, but I'm afraid the knobs have to be have to go because I think one of the main requirements is that it's thin can easily slide into a notebook, carry case or something else. It's really as Tiny as possible the size of a credit card or something like that. So as I said in the first video, I'm going to abandon uh the approach I've used with the uh previous two just very, uh, quick prototypes cuz I didn't put much thought into them I just wanted them uh for my own uh use and uh, so really I think I'm going to uh, ditch. Well, I've got no choice I've got to ditch this entire case because I can't be.

you know, wasting all of that volume in there I haven't got room for the knobs. even the displays are quite thick. Look at those there, you know it's just it's just not going to work out. So have to ditch the entire concept of that and get a smaller case and let's take a look at them.

now. the case I'm actually going to use is what? I really? and I actually? uh, keep in uh, stock? um because I think they're very useful and they're probably one of the most universal cases on the market cuz they're heavily copied now. um I Got these from Um Altronics you can buy from Altronics and J car here in Australia but overseas they come from Bud Industries or they come from a whole bunch of different manufacturers, one hung low Brands they all make the same Uh box I Um, so much to the point where I don't even know who the original? Well, the originator of these cases Um actually is what company first did them, but everyone seems to have copied them and I really like them. and they're available in um not only several physical Uh sizes, but also within each range.

They're available in different heights as well. and uh, this is like the uh, the big 100 by uh 190 mm one sorry I don't know in inches for you Yanks Um, we've got the smaller 80 by 150. we've got the 60 by 120 m and we got the tiny one that I'm going to use here which is the Uh 50 mm by 90 mm and it comes in uh four? Well, no sorry. three different uh Heights available.

You can get it in 16 mm height 24 mm or the one I'm actually going to use is the 32 mm height one and I'm going to mount the connectors on the end like this, but aha I'm not done yet. um I've got a trick up my sleeve that not only saves cost, but also halves the height profile. So before I go into that I'll just show you inside these. They actually come with um end panels and uh, this particular one is in uh, two halves like this.

It's got uh, the four Uh mounting posts inside. for a for a PCB they've got uh, vertical PCB mounting guides like that if you want to mount the vertical board in there and the end grooves on these. actually um, support a 1.6 m PCB So you can put in a 1.6 mm standard PCB and you can use it as the front and the rear panels. Uh, if you want to get them uh, silk screened and you don't want to use ABS plastic or if you want to, uh, you know, have them.

uh, actually have circuitry might have LEDs mounted behind them or whatever. so they're really quite nice. and uh, these are, um, unfortunately, in the smallest model here which I'm going to use. They're not metal threaded uh inserts here, but if you step up to the other cas, you'll find that they actually do have the metal uh threaded inserts and they are quite nice and they're very similar inside.

Be one. uh, Word of warning: if you're going to use these, be careful. Some manufacturers actually have the Uh mounting holes. It might have the mounting holes in different locations or something like that, so just be careful.

Uh, if you are going to try and uh, get a case from a different manufacturer and the big ones are exactly the same. they come with the mounting Hardware they even come with rubber feet and uh, they've got come with the Uh rear, uh, front and rear panels and the metal inserts. and the bigger one is just the same as that. Again, so um, what I'm going to use is this tiniest little one here which is 50 by 90 mm.

but as you see it as I said, it comes in three different heights. this thing and this is the biggest one the 32 mm. because not because I need the height, but I actually need half the height and you'll see why. and I Think this is a rather clever Uh product design decision that will not only uh, get me the one of the thinnest Uh profiles I possibly can for this product, but also half the cost.

Now, of course, one of the things with Uh using one of these cases with the end panels is: where does your display go Because a power supply has got to have a display and it's got to have switches, right? Obviously, I can mount my two binding posts on the end here, so just picture those mounted on the end like that. I can put on the standard 19 mm uh spacing aart that actually does fit in there. Not a problem at all. Okay, so I can mount those in there.

they go onto my PCB which is mounted in there and I can put. just put some little wires going down to the board down in there. but and I can on this side. I've got my USB input connector for the power supply and that's it.

So somehow I've got to put my display and my user interface, my switches. and no, I'm not going to make this thing just PC controlled I Want this to be Standalone so that it'll have not only a voltage, be able to display voltage and current either a single display or a jeel and it's got to have buttons so that you can use the thing independently of any software. if it's just software only. I Think it just loses all the appeal of that uh ability to operate it from virtually any 5vt you USB power source I Don't want to have to boot up the machine and run some software and all that sort of stuff just to Output a voltage.

It's ridiculous Anyway, so how do you get the display on this thing? I Hear you ask? Well, you can cut out holes. You know, the the traditional approach using something like this might be to machine out you know, the displays and machine out the holes for the Uh display and things like that. But really, that is additional uh cost and you can't really avoid that if you want a top surface on this thing. But I Got the idea of thinking what if I just split this in half and check out these two halves.

What do you see? Do you see any differences between these two halves? I don't It's because there's not essentially any difference apart from a tiny difference in the diameter of those uh mounting holes there because one is designed for the counter syn um, screw to go through on that side and the others a slightly smaller diameter for it designed to be screwed in like that. But apart from that, they're identical. So I got the idea of thinking, why don't I just instead of using the whole box, use half a box like that and I've instantly haved my profile like that I can still mount my connectors on stick with me I'll show you how I'm going to do that and so so not only have I half the height profile on there, but I've halfed the cost I can use both halves of this thing cuz who cares if one's actually got the protruding Uh holes on the bottom and one hasn't I'm not that fuss. the thing's going to be used like this.

So how do you get the front panel display? Well, you mount your PCB in there and you just get a clear PEX cover to go over the top and you have it and then you can see the display through the clear perspex cover. and it just so happens that those four mounting posts up there, there's a little height difference in there I'm not sure if you can see it, but let's get in. there's you know, a couple of millimet in there where that, uh, where any clear perspects, um, thing on the top front cover can just butt up against that in there and just go over the edge like this and it will fit in rather nicely. So imagine that with a nice clear thing on it, you'll be able to see the circuit board inside.

You can mount your display on the PCB you can have some standard tacked switches coming up through holes in the top, and Bob's your uncle, All right. So what do we got here? We've got one half of a very cheap case. I Can get this case for like $250 uh, in reasonable quantity even here in Australia let alone, uh, overseas or something like that. But because I can use two halves of it I've half my cost to A125 for a nice little compact case and it's not.

And it's no bigger than a credit card. and well, here's a credit card. This is actually the swipe card to uh, get into my uh office here and uh, it's You know it is no bigger than that. In fact, it's slightly, uh, less height than a credit card and just a fraction wider like that.

Of course it's going to be a bit more when you include the Uh The Binding post on the end, but let's not fuss over that and it's going to be very thin. Like that. We're only talking. You know, the perspex cover will take the top bit like that.

we're only talking our 16 mm, 17 mm tops cuz it does have a curved bottom on it like that, so it will. It does rock a bit on the bottom like that, but hey, that's a feature, right? And we, you know, look at the difference now in uh, thickness between these two. there's a huge difference. and we're going to do away with the knobs and just have the buttons.

Those tactile buttons protr SC in from the top here. just like these. but uh, these little tactile buttons but with an extended shaft on them so that they're the right height because you can buy these switches in different with different height shafts. It's just a different auto code on the uh end of the part number.

So there you go. It's nice, simple, and compact. I Really like it and I know some of you are thinking am I going to have room to mount these binding posts on the end. Well, if you look at it, um, you have to these things um, don't have.

You don't actually punch a round hole for these. you punch a uh, sort of a flattened hole and there's plenty of room in there as you can see to uh, plenty of height, top and bottom to uh, you know, get a reasonable front panel. reasonable amount of material top and bottom for those two holes so that should fit in there nicely and that will be actually where that ruler is will be the height uh will be the exact uh height of my perspex panel. It'll uh, sit in there like that so I should be and because it'll wedge up there the Uh panel itself.

the front panel will actually be. It'll sit in that Groove in there and be wedged between the top. So I slide the panel in on both ends if I want and especially on this end, slide it in and that'll be held in place by the four screws that hold on the top of the perspect plate. Not a problem, should work, a treat.

And then of course, once you've uh, chosen a well tentatively chos a case like this, you've got to make sure that all your major size components are going to fit and your amount of circuitry as well. So the biggest component uh on this thing is going to be the uh, the Uh Little 2 wat uh DC todc uh isolation converter in here which allows me to get my isolated power supply because yes, I want this thing to be isolated so you can make it into a split Supply and other stuff. As I've mentioned I Think that's an absolute essential, but it's um, height is actually too high. It's not actually going to fit in there cuz you remember, there's got to be a PCB mounted on top of there.

It'll be a standard 1.6 mm if we needed to shave off, uh, some extra height there, we could go for a 0.8 mm. PCB but uh, that will cost a bit more and uh, be a bit less uh, uh, rigid than the 1.6 so that's you. know it's just too high there when you include a PCB on there. but we can certainly lay that down flat.

and there's more than enough height in there. and if you actually measure it, there's um, enough height for 1.6 mm. PCB plus this thing to mount flat. Not a problem at all.

and uh, based on experience based on my, uh, previous designs, um here I know how much, uh, roughly how much circuitry I'm going to have in this thing? I've uh, got an idea for my display which you'll uh, see in, uh, a future video. I've got a novel idea for the display solution. uh no, I won't using the same 7 segment displays I've used here. So uh, so I've got to fit.

You know the display in here I've got to fit the switches I've got to fit the circuitry and ideally I want it all mounted on the top side of the PCB in there because if I go for a Jew sided uh load on my board I can mount components on the bottom. You can see there's a little bit of uh, you know, height in there on the under side of the board. I could certainly mount a whole bunch of surface mount components on the bottom and if you need really needed the space, you could do that. But a two-sided load board is going to cost more than a single-sided load board.

So ideally I want all my components mounted on the uh top and my board of course will be um, it could be square like that but I need it to be routed out here and poke out. You know well not poke out but come to the edge here. So then I've got my uh USB connector which uh, just uh pokes out the side here and you can plug in the USB but this board here unless I need the space doesn't really have to come around like this and go all the way out here. so I'm probably going to make it uh, flat on this side, just behind these pillars, go around, have a little routed cutout, go out to the edge.

So I've got my USB connector and that will be the size of my board and my uh display will show through the clear uh perspect top which might be you know a millimeter thick or 2 mm or something like that at most because it doesn't have to be strong, it just has to be uh, you know, uh mount on the top and uh, easily be laser cut and I don't know how much that would cost, but I know it's it's It's going to be pretty darn cheap because it's going to be fairly simple and it's not a real big thick 10 mm thing or something like that should be very cheap. And so that's my um uh case solution for this: USB power supply and I think it was, uh, quite a bit of a novel idea to use these two halves and then you know the cost of my display. Sure, half of the ones will have these holes in the bottom, the other half won't I may have to even. uh Supply possibly um, slightly different.

uh screws, slightly different diameter? uh screws to, um, go into each one. but even if I have to do that, it's not really a huge hassle. I probably won't have to I'll just they'll be slightly looser fit on these ones and slightly tighter to screw in on these ones up here. But not a big deal.

And of course, one of the problems with choosing the housing for something like this is there's no shortage of, you know, little small ABS Jiffy boxes like this on the market. they're you know a diamond doesn't you go to Uh Digi Key or you go to any of the U uh major, uh uh sub you know, uh, enclosure supplier websites. there's a whole list of them on the EV blog. Wiki By the way, if you go to Eev blog.com Wiki there's a list of um, enclosure manufacturers uh on there and you know there's a dozen of them and uh, they all make you know a dozen different little cases so it can often be hard to choose which ones to pick.

But I like these cuz I've used them before it just so happens to fit my height requirements is just big enough I can split in half to have the cost and there's you know, quite a few little things which are added up which I think made this probably an ideal solution for like like this: I did did look at uh, you know a few others on the market and they just seem to have some sort of showstopper somewhere along the way that was slightly too big, slightly too small, didn't have enough height, didn't have the right mounting holes, all that sort of uh Jazz so you know that can? You know you can spend weeks and weeks just searching for the right housing up front for your project. It's crazy, but if you want a nice looking product in the end, rather than you know if you do, design your circuit board first with all your circuitry. Everything's nice and it all works and you're happy with it. You might have to redesign the whole thing to fit in a particular housing.

so making the housing Choice up front is uh, very important for a product like this. but it's not the same for all products. But in this particular case I think the housing Choice was you know, 90% of the work. it's not absolutely set in stone.

I Might find that there might be a showstopper something like that at the end, but I don't think so I think I've uh, Tak Tak enough things into account that I'll make the damn thing fit into this uh case. So um, hopefully Murphy won't intervene and uh, you know, come along with a real showstopper. but uh, I Expect this to be my case and it's quite small. compact, thin Sleek I like it I actually like the uh, you know the curved nature of these things and these little um, side bits on here for a bit of grip like that.

it's just it's these are really quite nice case. So that's the housing and I deliberately did it up front because I think it's very important to get that right. First of all, I mean anyone can do a USB uh power supply actually design the circuit, Lay out a square board and put some rubber feet on the bottom and bingo, you have a USB power supply. but to have something that's reasonably, uh, funky looking into a nice uh rugged uh case or something like that, which is in a nice form factor and cheap as well.

cu. One of the main requirements of this Supply is I want it to be as absolutely barebones cheap as possible without going to uh China of course I still want to get it made in Australia I want to get my you know, my board from New Zealand again and uh, you know a lot of the cost will go there. So I want to choose the uh, cheapest possible uh component and housing solution that I can get away with? That still has you know that nice rugged look and feel and this should be pretty darn rugged. It's tiny, these only protrude out here.

there'll be nothing protruding out the other end. just be the USB connector. it'll have a tough PPC uh cover on the top and you should be able to toss this thing around. No problems at all and it should last a lifetime.

So that's the housing. If you uh, like this video, please give it a thumbs up. If you like the series, please give it a thumbs up. and uh, comment on the Eev blog Forum that's where all the discussion is for this thing and uh I'll follow up with further Parts As I designed, this thing should be interesting.

Catch you next time.