Hi. In a previous video, we took a look at designing your own custom LCD and I'll link in that video at the end and down below. If you haven't seen it, this is basically a part to follow up to that's going to be part two of several parts to come and where we left off before is that we actually had designed our own custom LCD and I've done tutorials on LCDs I'll also link those at the end as well. We designed our own, specified our own custom LCD, and went off and got a quote and we're currently getting that manufactured.

So as I mentioned in the previous video, you don't really have to go to this sort of detail that David's gone to here to specify this particular LCD that we're getting for our new micro supply project. We've color coded all sorts of various things over here, so we gave them this table to fill in here for the P-n information, and they got reasonably close to what we wanted, but we'll have a look at the final datasheet that they sent us, so you don't necessarily have to go to that sort of effort to detail effort to actually specify your LCD, but the more you specify it upfront, the closer it's going to be to exactly what you want. You can almost design it on the back of a napkin with a sketch, and they'll pretty much be flexible enough to do that for you. So the next step is is that we said yep, Go ahead.

We paid our hundred and forty dollars I think it was 140 US dollars This includes the tool in charge and we're gonna get five samples which we haven't got them yet. so that is just ridiculously cheap. I mean hundred and forty bucks including the tooling and five LCDs delivered it did when I was a boy Anyway, um, this mate. this.

you may not be able to get this low cost if you did, say the back of the napkin you know type approach. We actually gave them the full DXF designed it, the actual segments in the full DXF file and so they probably had very little work apart from actually routing the thing and doing up the data shape. And if they have to actually design and draw all the segments based on you know, your napkins, get your something like that then they're probably going to charge your extra tool in for the time and effort involved in that. So this second part video is about the data sheet that they've sent back because once we send them our drawing for the LCD then they'll draw it up in their CAD system whatever it is and get ready to manufacture it.

They will send the data sheet back to us to actually approve. They want to steam, you know, basically sign off on and say yep, go ahead. That's what we won't be happy with that. Go ahead and manufacture our samples, so let's take a look at that.

So this is the data sheet that we've uh, sent out. We have blinked some various things on here and it's a multi-page one as we'll see at the moment, but they've sent back basically the detailed dimensions. the individual are segments and things like that. The specifications for it say: Stn positive Mode 1/8 duty Cycle quarter bias, six o'clock viewing direction I've explained all these specifications in the previous video operating temperature range minus 10 to plus 50 operating voltage 3.3 64 Hertz Framerate transmissive and the back polarizer is a reflective so it's going to be a reflective type LCD ie.

no a backlight on this thing. Alright, so they've sent the full pin table. This is after they've done all their routing inside there which will show the routing in a minute and this is the entire pin out for the thing and they basically got the. They pretty much did most of the grouping that we wanted, but that will be independent.

Like I said in the previous video, like if you've got a segment up in this top, left, top, right-hand corner here and you want to connect that segment over to a pin on the bottom right here, that's just going to screw up your routing and things like that and then basically not going to be able to accommodate your request for things like that. And so that we've got the full pin Table map in here. We've got the 40 pins 20 down each side and you might notice that these lines across here. look at the min and Max here how they've got a line across that and what that means is that you can't turn on those segments individually.

So it's just it's the word. it's signifying that that's the word men. and it's just one segment to turn on the word men. And you can see that they've also got that down there for the battery symbol for example.

So they're they're actually connected together and like those two decimal points, it will the colon like in there for like a time. between those individual are segments there. So that just signifies that there are tied together. And here's basically there are routing drawn.

Now not all data sheets actually will show you this, but they've really gone to town and like we can't actually zoom in on this so it's not like the real route in. you know, the actual photo image of all routing paths like your Gerber files for your PCB for example. it's not actually that and then it actually shows where the segments look. It shows that the the common over here.

Okay, it goes to these pins one through the pin. eight. There there are common pins and the rest of them are the individual segments, but it basically shows you how they all tie together and like. It shows that this seven segment digit up here for example is all on the one line like that and that's how they're multiplex and you'll see that reflected in the mapping pin map in a segment mapping table that we saw before, but that's not quite arrived.

The Groovy: It just shows how they actually do the routing inside. Something like this. There's a lot of work that goes into this. This is a fairly complex custom LCD with lots of segments, lots of pins with eight Commons, and like 30 odd segments as well.

So it's yeah, it's getting up there in terms of being able to route this thing efficiently on just the two layers there. and it looks like we've actually had like a PDF rendering type arm error here from AutoCAD or whatever it is. The CAD package that they're rendering from. The segments are all showing like all joined together here and we've confirmed with them.

Yeah, that's obviously not how the final arm LCD is going to look, so they kind of like just goofed up a little bit there. But as you can see, this supplied this full data sheet for the thing and this is going to match the samples that we're going to get. Okay, so what we're going to need now is some sort of driver, a demo board, or your final product board. Whatever it happens to be to actually drive this LCD when we get these samples in.

As I said, we don't have the samples yet, they're on our way. but we'll get a board manufactured and we'll have something ready to go so that the LCD will be able to plug it in because we're going to need because this is a quite a complex LCD with eight Commons and 100 over a hundred segments, we can't just drive it directly with the Stm32 micro that we're actually looking to use in our final product here. So we need obviously to use an LCD driver chip and I've mentioned this previously so we've decided on the whole tech 16:22 so let's go take a look at that one. The advantage of this is that it basically only needs three lines for the microcontroller.

It's basically an SPI interface so we have our our clock mosey and chip select. Oh, this chipset can actually read the data back out as I'll explain in a minute but we're not using that functionality which is driving the LCD and we don't really care to get any data back. That's a really in this particular product and this particular implementation that we're doing here. There's just no value in doing that, so you might as well save a line.

So as I'm sure I mentioned in a previous video that there's a trade-off between trying to either find a microcontroller, even if you can find one that can support your particular LCD that trying to do. In this case, there are microcontrollers available that do have the eight Commons and the number of segments required to drive this LCD but they typically push you in or much bigger pin package microcontroller which usually has more memory than what you need and more other resources and everything else. A bigger, better ass micro that you're going to pay a lot more for it So often it's actually cheaper to use a simpler microcontroller with no built-in LCD controller and using an external LCD controller like this whole tech one here. So this is the whole tech HT 1622 and it does a bit more than that LCD driving as we'll actually see here and it's you can even buy it like an hourly Express for less than a dollar in one off quantity.

And you know there, we've got other sources that can actually get this quite cheaply and the do. It's actually cheaper to get this whole tech driver chip than it is to buy and spend the more on the microcontroller to get the model that has all those pins required. As I said, so it's from a cost point of view. it's better and also from a PCB layout point of view as well.

You can actually put the driver chip next to your LCD right next to the pins. You can round out the pins properly. It might mean you can use a two layer board instead of a four layer board for example. so those sort of factors can influence the final cost of your design.

Um, you know, could saving cents here and there kind of matters in you know, not even like high-end consumer type stuff in the millions, but sort of at the lower end as well. The high imagine that you can get in your product, the bomb costs versus the basically the retail or sale price of it, then the better off you're going to be and you can spend money on a better case or better switches of it overlays or you know, something else. So if you can save money, do it where you can. But also from as I said, a layout point of view.

if your micro, your micro controller can be over on this side of the board up here and your LCD controller can be up on this side and you've only got those three lines going. That SPI bus going between it and the microbe might be over here because you might be using the analog to digital converters in it or something else and they might be nee analog parts For example, in your LCD can be separated right up here, so there's lots of advantages to using a dedicated chip. they're often just easy to use. You don't have to dick around.

Some of the microcontrollers are quite complicated in the way they drive their LCDs and programming them and things like that, so this is quite a reasonable solution. So we're using the HT 16 22 with eight comments and 32 segments and this is actually a pretty groovy little part. Not only does it have a watchdog, timer and time-based generator, but it's got a buzzer generator as well, which we're going to use for. you know, hook up a buzzer to it and it can actually generate two different frequencies, so that's really good to kill and 4 kilohertz.

so you can get different tones and stuff like that so it's very simple to use. Now the interesting thing about this 1622 is it's actually available in three different packages: a 44 pin L QFP a 52 pin L Qf P, and a 64 pin L Qf P. And why I hear you ask? Well, different sizes for different technology products, for example. Like you might think, think that the 64 pin L Qf P is bigger, but it's actually not.

It's a 7 millimeter by 7 millimeter. If you have a look at here at the dimensions here, that's the dimension. The pin pitch should go down here on this inches. Rubbish.

We want millimeters ly This point. Four millimeters Pitch Pin pitch. What a pain in the ass. I'm point five is quite small.

Point four is starting to get. you know, really pain in the ass category. but the other ones up here. For example, the fifty-two pin is a 14 by 14 millimeter, so it's actually four times the area than the seven by seven millimeter one.

The seven by seven is actually one-quarter the physical size of the other one, so you know a huge difference for the same chip. Obviously some of the pins are not going to be used on the different configurations and then the and that one, by the way, is a one millimeter pitch. So there you go if you want to sold all those by hand. One millimeter Geez.

Stevie Wonder can solder a one millimeter pitch l QFP No worries. And the 44 pin l Qf P up here is once again, it's a bit smaller again than the 14 by 14 millimeters, so if you physically got less border area then you could potentially choose this one. and you're a point eight millimeter pin pitch. So it's still quite reasonable.

So, but how you might not be able to get all of these with the same sort of availability so you may be stuck with the one that you can get B incoming gutter when you're in your bill of materials. If you actually order the wrong part, you know you may get our supply. That's it. So yeah, I've got I've got a ton of those 10,000 of those HT 216 22s I'll get to a good deal on them.

They send them to, you know, find that you get the completely wrong pimp itch and you just screwed. So yeah, you've got to be careful. This is where you have to specify the exact configuration. Where is it? Let's have a look.

Actually, this one's further interesting in that it doesn't give you an exact bomb part like a like a order in part number on here to actually get this right. so you would have to actually specify it and double and triple check with your supplier that you're actually getting the right one. Normally in data sheets like this, there's like a table that actually you know gives you the exact or durable part number so you cannot make a mistake. You know, with the extra digits, that'll be H2 HT 1622.

with you know, some weird digits on the end to order that particular package, but in this case they don't actually have that. which is really kind of annoying. Whole tech. Anyway, just watch out for your your pin pitch on your packages and what type of package you got because if you go to BGA for example, that's a different might change your assembly requirement somewhat so that can add to Causton yield and all sorts of things like that.

So this is quite nearly their pad coordinates. We don't care about all that, but here's the pins for the sucker. So we've got our chip select. We've got our Reed pin, which as I said, we're not actually connecting in this particular circuit because we don't need to read back the RAM contents and things like that.

Only if you want to store that, use the RAM inside this chip to store the data so that you don't have to store it inside your microcontroller. That can be handy if you've got a real tiny micro controller that's memory limited and stuff like that. You can use the map in the RAM mapping inside the LCD driver chip and then to hold all that data and then just read it back If you need to manipulate it or do whatever, read it back later. So but we you don't have to use that, you can just push up the data so the right pin, the data which is a bi-directional thing.

we've got power oscillated the from an external clock saw so we're going to clock on that and the also the operating voltage which is you generally hook up I'll show you the example circuit in a minute, You just generally hook it up to a pot there so you can adjust it, or a digital pot if you want to adjust it digitally. and there's three, four, three unconnected pins there. so let's go down and have a look at. It's got timing diagrams and all sorts of things.

It's got watchdog which consent. There's an interrupt pin as well, which can interrupt your microcontroller that might be handy for various system applications. We won't go into that. and there's the example application circuit and this is it's patented.

They make you aware of that on every single page, thank you very much. and you just put a variable resistor. It's basically just a pull-up so you can put a fixed resistor or a pot in there. It's typically like a 10k pile or something.

We've got our piezo buzzer on there. make sure it's actually a piezo transducer because there's a difference between a buzzer and a transducer. A piezo transducer is just the transducer. There's no building oscillator, so it needs the oscillator built in to either your microcontroller or this particular thing.

But a buzzer actually has the oscillator build and so all you've got to do is apply 3.3 volts for example, an output logic high on your microcontroller and it starts to buzz at the predetermined frequency. The good thing about the piezo is that you can basically drive it at any frequency you want, so you can get different tones and whatnot. whereas that's what this chip actually supports. 2 kilohertz and 4 kilohertz tones.

But if you're driving your piezo directly with your microcontroller, then you can, in theory, just drive it at any frequency. You could sweep it, produce tones, and play music, and do all sorts of wonderful, weird, and wonderful stuff. Make it talk, maybe would have Peas I sound decent. You'd need a decent DAC on there to do that.

Anyway, it's a non sequitur, so that's that's all there is to it. And then you just hook the LCD directly up to the common and segment drivers. It handles all the biasing because the bias in for a multi segment LCD is actually quite complicated for an 8 common one like this. And as I've mentioned in previous videos, although I probably have to do a dedicated video on multiplexed LCD Driving this quite complicated actually.

multi-voltage levels like this. so this is for example, a common. this is a just a microchip application. Note here it's got quite some decent information, but they're all these different voltage levels in here and your LCD driver has got to be able to generate all these different levels because as I've mentioned before, if you the whole idea is that you have effectively over time, you want to have a net DC level of zero on your LCD otherwise it could potentially damage your LCD So that's what these are.

Dedicated drivers actually take care of All this, they generate the bias voltages as they do everything else. Beautiful. You don't have to worry about it. And for all you math nerds out there, let's go and have a look at this.

I Try to say Maths Math like we're supposed to say in Australia but I can't say it, my tongue just doesn't let me do it. So I have to cop out and use the American math math. You can actually this formulas to calculate what's called the discrimination ratio which is basically your you know in calculating the DC values your RMS values in there of on and off segments and look we can get quite complicated for a 7 segment for a 7 common LCD like that so you know that's it. But like I said, if you want to, if you want to try and drive the LCD yourself using your own circuitry, this is that.

All the sort of stuff you have to do. whereas this is why you use a dedicated LCD driver chip either the whole tech one which we've got here or ones that are built in multi segment, multi common ones that are built into your microcontrollers. They handle all this stuff and it's all taken care of for you workers and it could even get more complicated. You might have to like bypass and with some caps as well, so that's you know.

quite significant added components to your PCB doesn't really cost a huge amount, but there's cost in terms of assembly time, of placing the parts, Bill of Materials and all that sort of stuff. Not to mention the component space on your PC beams. but the whole tech we've got it doesn't need any of this. generates at all internally.

Brilliant. So there you have it. That's just a sort of like a follow up video and intermediate step quiet to get your custom LCD manufactured. So hopefully in the third part of this custom LCD video series, we'll get the real samples back.

We'll pair them up and see how they work. So if you like that video and you like the series, please give it a big thumbs up because that always helps a lot. As always discussed down below, Eevblog Comm links and all that sort of stuff. You can support me on patreon links always down below at YouTube stuff Bell icon do that catch you next time.