Hi, it's USB Lab Power Supply time again and I promised that I would uh, talk about the display solution used on here because I said I wanted to go away from the LED display uh, used on my previous prototypes and uh, possibly use something else because you know I've been talking about this uh, you saw in the previous video the housing display I'm going to use like a clear uh thing on the top possibly so I'll be able to see whatever display solution is through the clear perspex or polycarbonate uh, cover on the front So there's no need to worry about things like cutouts because when you do, when you use displays like these seven segment displays or LCDs or something like that, um, you'll notice that you have to add cutouts uh to, you know to see the display through on a typical front panel and they're a pain in the ass to get those aligned. It's extra cost in manufacturer and things like that. So with a clear uh, you know, display window on the front of this thing, we can use pretty much anything we want LCD LED whatever and you'll be able to see it straight through. So why am I going away from these seven segment lead displays? Well, it's pretty obvious they draw a fair bit of current now.

Um, you can get really efficient. Uh LCD lead displays These ones are LTC 7424 Um, they're a very nice little display and the reasonable cost? I We'll have a look at the costing in a minute cuz that's what it's going to come down to. Really for the display choice this time around. So these aren't bad displays, but they're going to take at least a couple of milliamps per segment to get them at a re.

You know, a usable brightness. Um, in, you know, a typical uh environment. You know, like a lab or an office, or a room or whatever. So let alone, um, outside.

Let's say you got, you know, a good grunty 5 milliamps per segment. That should give you a fairly decent brightness. Well, you could have if you're just laying an eight with a decimal point. you could have eight of those on for each one of those digits.

So that's 40 milliamps. That's 8 * 5 milliamps, 40 milliamps right there for one digit. And of course you wouldn't. Uh, with these sort of solutions, you Multiplex them.

Um, so you know you can get a maximum average. Well, a maximum value of 40 milliamps for the entire display. You know, in a normal project it's probably not a lot in a regular bench power supply. Not a huge amount, but this thing.

We've only got 500 milliamps. Uh, total. We're ignoring power here. We're just, you know, 500 milliamps at 5 volts.

But then you got the loss of the Uh converter, the isolated DC to DC converter. And to draw 40 milliamps that say, 3.3 volts. That's a fair whack of your power budget. So really bad idea to do the Uh LED display.

But as you might see, I'm going to end up using LED but you'll see something a little bit different. Come to that. Now the obvious solution everyone says: use LCD Great. Okay I like Lcd's displays as much as the next person, but we'll take a look at it.

they're a similar cost uh solution. probably even a little bit more than these seven segment lead displays. So really, I'm trying to keep cost as low absolute low as possible on this project. So LCD well it's A, you know, a nice solution.

a it's expens. it's you know, it's not cheap. Um, unless you go for one hung low, get them from alib Baba in uh China and H it's just. it's really horrid.

It's not something you want to uh do for a project like this. I want to stick to like a name brand LCD something that you know is going to going to be available in 5 years time or something like that, not just some one batch Wonder from uh one hung low on Alibaba So the LCD solution H It's not bad, similar cost, but then you've got to find an LCD uh, a microcontroller with an LCD driver to drive the thing. I'm going to come up with a really lowcost display solution. It's not nearly as good in terms of uh, you know, direct reading and things like that as you'll see, but I think it's reasonably clever if you want a really Ultra lowcost solution, let's go to the web.

All right, let's jump straight on to Digi Key shall we? And we'll search for our Ltc7 uh 4724, which is what I've used in my previous one. And here it is and uh, let's scroll across and take a look at it. It's from light on and they're a really nice little compact displayer. really light and there really small.

but uh, they're $292 in oneof quantity. Well, let's uh, go in and look at the price breakdown for those, even if I'm making a th000 of these things Buck 30 each, right? So that's $2.60 Bam right there in your cost. So remember that Well, even if we had like one of them, for example, Okay, you're still talking A130 in a thousand of quantity. Not that you know when you're trying to shave cents off your production cost and things like that trying to keep this thing ultra low cost.

Um, that would make this by far the most expensive component on the entire board. Well, it' be the most expensive uh, apart from the DC to DC converter, but that's always going to be the most expensive component in a little USB power supply like this. And by the way folks, for all those who are complaining or asking, why don't I make this thing you know capable of two, you know to utilize the US B ports with 2 amps or 3 amps or whatever the latest charging standard is in USB 3.0 It is because the DC Todc converters are very expensive and they don't linearly increase in cost Usually to go from say a uh 2 wat converter which is what we need for a 500 milliamp solution up to you know, a you know, a five or six watt uh version or even uh, higher that we need for a higher power solution. It's just they you can double, triple, quadruple your bomb cost right on your isolated DC to DC converter like there.

And of course I want this project to be isolated. so that isolated converter is an absolute essential. So if you're uh, if you're complaining about that and wondering why I don't use it, well go and check the costings for these DC to DC converters and you'll find out for yourself. And if you're wondering if they're a cheaper LED uh, seven segment Solutions uh out there, not really here I am I've sorted all of the lead displays on Digi key seven segment ones by three and four digit ones and let's uh, sort by unit price of say 1,000 and let's have a look at it.

Well, we got uh something here. We got a three-digit display which is 86. That's a bit cheaper, but they don't have any in stock. Look, what's the point? We get down to the display we're using down here which is a similar cost.

We're talking A130, so you know if you're talking Digi key here, which is what you really want to base a project like this on unless you want to, uh, go for Ali Barber or something like that in China. The prices are pretty much set at say $130 per thousand of quandy. You might be able to get the price down a bit, but it's not that great. But as I said, the current consumption of a 7 segment display is fairly prohibitive.

Okay, I've used my parametric search here to search for LCD displays. I've limited here to three through to four digit ones cuz that's really all we need. We can get away with three. Three and a half one would be okay and four digigit one will be okay too.

So I've applied the filter to that and let's go over and let's search for our thousand of quantity again. Nice good ballark figure when you're working on a design like this cuz I think it, you know it'll selling the ,000 or two. so that's the price. Target I'm going to shoot for and uh, let's have a look.

We got some nice looking lumex ones here and I've seen these before and we're talking. You know they're cheaper than the seven segment lead display solution. Okay, we're talking 95 cents here. They're available in, you know there's a decent quantity available in Digi Key.

Not a huge amount, but they're there and they're 95 cents a pop. Well, that's cheaper than our s segment lead display display solution lower power so it's not a bad choice I Guess you can, Uh, certainly go for that. So that looks like pretty much, uh, the best solution there. and yeah, they jump up in price pretty quick.

Look at that, you know, $250 Bam! and um, trust me. I've searched Mouser and things like that and it doesn't really get much. uh, better. So from the uh, reputable suppliers, you're talking 95 cents or almost a dollar for a three-digit uh.

In in this case, this is a three-digit display solution and we can actually take a look at the data sheet like that if we want. And we will because that comes into uh, how many? uh well, what sort of microcontroller we need with built-in LCD capability to drive this thing. Now for some reason I'm really getting Deja view on this I think I've gone through all this before in my um, battery powered power Supply thing. So please, uh, forgive me if I have gone through this before, but we'll do it again.

This uh to drive this uh, seven segment display here. this 95 Cent display just one of them. Uh, by the way, we need a microcontroller that has one common pin and we have uh, well, basically uh, 23 uh, different segments. So we need a microcontroller that has only that has support for one common pin.

All of them will have that, but some will have. you know, two, three, or four common pins. Um, but we need one common pin with 23 segments. So we need to find a microcontroller that is uh, capable of driving this LCD display.

Now what microcontroller? I'm actually targeting Uh for this is an At Tiny 48- Au and it's um, it's one of the um, you know, it's one of the tiny range of microcontrollers. Unfortunately They only have 100 quantity uh price brakes here, but that's 886. So um, as you can see, that's cheaper than uh than any display solution itself. So if you take out the display and you take out the DC Todc converter, then the microcontroller becomes the most expensive component on your entire board at 86.

But of course, this one can't drive a microcontroller. so let's find the next simplest one that can drive this. LCD Okay, what I've done here? I've decided now I'll search for every brand microcontroller on the market available from Digi key according to their parametric search that has an LCD display. So I've uh, gone through the Uh table here and I've searched out all the ones that have LCDs and I've sorted by thousand of price and right up the top.

Here or at the bottom of the price scale, we have a free scale RS 08 doesn't look like a 28 pin, uh S Soic doesn't look like it's going to have enough pins. we're talking 68 cents in, off quantity and then it jumps up to the next one jumps up to some pick uh 16 LF 1900 Series micros I've actually used those before. they're not bad and uh, they're like you know, jump up to 99 C A doar something like that. So we've automatically jumped up like an extra 20 cents in our price.

but these are only like the 28 pin ones cuz we've got 24 pins already just for the LCD including the uh common and we need the power and ground so there's 26 and that only leaves two pins available which is useless. So we really need to search for ones that have, uh, greater than uh 28 pins. so let's try that all right? So what I'm going to do here is just limit these to 44 pins through to 48 cuz I don't want some monster device uh and I want something that's got an adequate number of pins and I know a 44 pin device will be be able to do what we want. So Bingo I've searched again and as it turns out, the Uh P 16 LF 1934 it's still kept our thousand of quantity here and sort of P by Price Bingo we've automatically jumped up to $168 That is almost uh double what.

Um, our previous at tiny 48 device is. and there you go. and I'm still searching every one of these manufacturers as you can see right to go for this LCD solution. We've saved a little bit of cost going from our LED over to our LCD but then we've doubled the cost of our chip.

Crazy! So just there you started to see the tradeoffs between cost of your display, your functionality required in your microcontroller to drive it, and things like that. So I got to thinking, well, how can I lower the cost of this display solution cuz I think the LCD is still, you know I think I can get a lower cost than that at uh, you know what was it? 96 cents or just under a dollar or something like that? I can get cheaper Again, probably not as good in the seven segment display department, but we'll see now. One obvious way to do this is to use a lead seven segment display. but instead of using an expensive actual seven segment display like used on this one, you can actually replace these individual segments with IND idual.

LEDs because LEDs are really cheap when you buy them on a reel of like 3,000 they're like a cent each or something like that. They're incredibly cheap so you can actually uh, manufacture. You could put like two LEDs there for each segment and you could even get reverse Mount ones. but they're a bit more expensive.

but like I use on my microcar reverse Mount ones mount on the back of the board, shine through the board a little, and then you could, uh, drill a little slot in your board on your PCB file and you can actually make your own seven segment displays out of individual. LEDs and it can actually work out cheaper individual leads for all these segments for the whole three or four digit display or whatever than it is to buy the completed lead assembly. But that's not my solution because that will save you cost. So if you're just after cost, that could be a way to do it.

But I want cost and reduced current consumption too. So what have I got up my sleeve? let's take a look at it. It does involve LEDs Some people aren't going to like this, but I want to hear your feedback whether or not you think it's a good concept. Let's go to the Cad tool and I was going to show you this concept on the breadboard, but it's easier just to show it in the Cad tool in the 3D View and this is what I have in mind here.

It is here: Tada It uses individual. It's a decade based individual lead display like this. so we've got a total of 32 LEDs here and allows us display voltage and current in these vertical segments up and down here like this. Now these are um, like a standard 0603 surface mount LEDs and like I said, they're like a cent each.

They're incredibly cheap, so this entire display solution costs 32 cents and it works as a well. It can work. um, as a dual display. You toggle between Vol and current down here.

So what we have is a vertical bar graph effectively of 10 LEDs for each digit like this. The Um: because we don't actually need all 10 for the Uh for the most significant digit over here for voltage and current because our voltage is only going to go up to in this case, it's Xx.xx Vols So it's 10 ms resolution on this thing. but we don't need to go up to 99.99 Vols right? We only want to go up to uh, like one or zero. Uh, sorry, one or two, say 20 Volts For example, this could actually go up to 29 uh, 99 volts.

So I can go practically to 30 volts with these only two. LEDs And there's no need to have the most significant zero on there either, because our decimal point is not here. It's here and here for milliamps. So um, the good: I What I like about this? It's a bit harder to read, of course than a seven segment uh lead display or a seven segment LCD display.

but it's a really cheap. It's like 32 cents or less. There's no hand soldering involved like there are with um, this, uh, LCD and this uh s segment lead display solution. So it's all done by the picking Place machine which helps reduce your assembly cost again, cuz you're not paying for that hand and Assembly labor.

So um. the other good thing of course is that this is a lower power solution and you would Multiplex this of course you've got a you would Multiplex the individual rows like this and you'll be able to see this on my um you'll be able to see this on the uh if I go into the 2D mode here they're you know a column based like that and on the bottom row they would go across like that so you Multiplex them all like that. Okay and it's um and so you've only got one lead on at any one time so your entire display solution is safe. If you want 5 milliamps per LED it's only going to be 5 milliamps cuz you would scan because you're only going to have one lead in each of these columns on at any one time.

Let's say you've got uh 12.34 volts. Well this Led here will be on to represent the 10 digit. This lead here will be on to represent um so that's 12 1, 2 and then this Led here will be on with three and then4 there. so it's 12.34 Vols And as you like, press the buttons on this thing I Can think it'll be quite neat because you'll see the lead sort of.

you know, scanning up the bar graph like this and then it'll count up and then well I Think it would actually be quite neat to actually watch it as you uh, you know, turn the knob or in this case I press the buttons cuz I'm not going with knobs, but I think this will work out quite well. Let me know what you think I Know not everyone is going to uh like this, but it is cheap and it's reasonably low power. Sure, not as low power as a segment seven segment display. but we're but it means that we can use our you know 80 C microcontroller instead of our $160 microcontroller for example.

uh and we can. um, so we've you know hared the cost of our microcontroller there and it doesn't and we've got a wider choice choice of microcontrollers cuz it doesn't have to have a build-in LCD controller. There you go I Think it's rather a neat solution. Let me know what you think if you like it if you don't like it.

but please just bear in mind that it is super duper cheap and it's easy to get. There's no, you know it just uses standard off the-shelf surface mount. LEDs I'm going to call it Dave's decade digit display I Don't know, is it catchy, but there you go. it's not.

You know it's not. new projects have done this uh, before, but hardly anyone ever does it. but I think there's still possibly a reason to use it here. a it's a bit novel B it saves uh, cost, and uh and uh you know machine assembly and things like that and easy to get parts.

It's not too bad on the uh powerfront as well, so there you go anyway. let me know your thoughts. I Think I'm probably going to go with this unless somebody can convince me otherwise to go with an LCD um solution cuz it comes down to basically this or a seven segment LCD Let me know what you think and uh as always, jump on over to the Evev blog Forum to discuss it and uh please if you like this video If you like this USB Power Supply series Please give it a big thumbs up. Catch you next time.