 Greetings Retro Computer Friends. Today I have a TRS-80 Model PC-1, the first pocket computer in the TRS-80 line. This sold in 1980 for $230 US, and it is essentially a basic computer. So by basic I mean the language basic. It is a computer that you could program in basic. So I bought this off eBay for $5.50 with shipping of $7.50, so they're quite cheap, and there's a particular reason why they're quite cheap. The seller sold this as for parts or repair, and the main reason for that is you could see on the LCD at this top side, this sort of burnt-in look. We'll get to that in a moment. The other reason why they're usually sold as for parts or repair, apart from the LCD, is that the batteries are usually flat, dead, not present. They're not hard to get. These are hearing aid batteries. Type 675, they are zinc air batteries. So again they're usually used for hearing aids. They come at least this one in a pack of six, and you take them out like this, and then you put them into the hearing aid, and you pull this tab. Now here is the original battery that I pulled out. You can sort of see a bunch of holes around the plus symbol. Those are actually air holes. So the purpose of this tab is not only to make it easy to stick into a hearing aid, but also to plug up those holes, because once you remove the tab, the holes get exposed to air, and then the battery is going to start to work. Even if you don't use the device that the batteries are attached to, the batteries are still going to continue to degrade because of the chemical reaction that's taking place between the zinc that's inside and the air that's flowing through the holes. I suppose you could stop it by taking the batteries out and replacing these sticky tabs, but that may not be the best approach. The best approach is probably just to get a whole bunch of these. So to open this up, you have to remove four screws. This one says serial number 09004947. There's actually a name sticker. The instruction manual that comes with this says that you can put your name on the name sticker and then stick the name sticker on the back of the pocket computer. So opening this up, we can see there is the, I believe this is the main CPU, underneath is another circuit board which contains the display chips, and there are four slots for the batteries. Now I've already filled three of them. To fill the fourth one, I'm just going to put the battery in, pull the tab, and we are ready. So there's a little piezo speaker over here, an electrolytic capacitor over here. This is the reset switch. It corresponds with a hole in the bottom. On the side, there is a port where you can stick this into either a printer or a cassette tape interface. So let's go ahead and put the cover back on, turn it over, and press the on button. And we can see that the LCD does actually work on this. So we can see that there is actually a prompt symbol over here and you can actually type things. So now if I hit the shift button over here, you can see the shift indicator up here. It does actually look like it's lit, but if I press shift, you can see that it gets darker. So the reason for this is that the LCD is manufactured for these. First of all, they're custom LCDs. They are 24 by 1 characters. So there's a little 5 by 7, I believe, dot matrix, 24 of them. But there are also indicators along the top. So there's shift, deg, rad, and grad, run, program. I think there's a reserved thing over here and a little dot over here, which you can barely see, which I believe indicates that the machine is doing something or other. Anyway, the reason for the LCD problems is that there's a LCDs are made out of two pieces of glass, top electrode and bottom electrode and there's liquid crystal sandwiched between them. So you stick the two glass pieces together with some tiny spacers and then you seal the edges around so that nothing can get in or out. And the problem on these LCDs is that seal. So over time, that seal actually allows moisture to get in. They didn't know it at the time because, of course, these probably wouldn't have lasted more than a few years anyway before the next greatest computer would come out. So anyway, pretty much all of the ones that you see on eBay will have these sort of black areas on the top where the moisture has gotten in and ruined the liquid crystal. There are also some other possible spots that you can see if you tilt. You can probably see that on the bottom. The bottom row does appear to be activated a little bit. Same thing on the top row. That may not be a contrast issue because I'm tilting this. That may actually be the seal. So the seal actually runs along the bottom and along the top. So this actually works. The only problem is the LCD. And the LCDs were custom so they are impossible to get new ones. Now I've taken apart another one of these because, again, they're cheap. And I've opened it up to show you what the LCD is composed of. Right. So here is a disassembled LCD. This is the LCD itself. It's just two pieces of glass. And you might be able to see perhaps some patterns on the inside. Those are the electrodes. The electrodes are made essentially of an extremely thin layer of metal, so thin that it's pretty much transparent. So the idea about how LCDs work is, at least for this one, this is just a simple reflector. It's a little bit burned because of my failed experiment where I tried to use hot air to drive out the moisture. Hot air also affects the liquid crystal, so that just wasn't going to work. So the idea is that the back reflector is stuck on to the back of the LCD, kind of like this. And then, ignoring these bezels and things, you have the polarizer on the top that sits like this. Now you can actually see the black areas. This LCD was just totally, totally dead because the seal had leaked completely. The liquid crystals inside were damaged so much that this was pretty much completely useless. So the idea is that with this particular type of liquid crystal, known as either Tn for twisted pneumatic or STn for super twisted pneumatic. So you have light coming in at any angle. The polarizer will polarize to, say, this angle, suppose. Now, if the liquid crystals are just aligned like this, then the light will come through, bounce off the back, and come out of the polarizer in the same angle so there's no effect to the light. So effectively, you get nothing, transparency. Now, if you activate the liquid crystal with electrodes, the liquid crystal will rotate like this. And I'm going to use 45 degrees because when the light comes in at, say, 0 degrees, it goes through the liquid crystal and gets rotated by that 45 degrees. Then it bounces off the back reflector and gets rotated another 45 degrees. Now you can see that it's completely perpendicular to the polarizer on the top and the light is not going to go through. So this is a particular type of LCD called a reflective LCD. There are other LCDs with back lights. Obviously, that takes more power. This is pretty much the lowest power type of LCD that you can have. It uses very, very low power. And that's why they used it in this because, you know, they wanted to use it with batteries and you would only get four of these. These are 1.45 volt batteries. There is actually no external power port to this, so you have to use those batteries. So the question is how exactly would you go about replacing one of these LCDs? And by replace, I mean actually getting a new one. So this is an experiment that I'm going to do, sort of inspired by Dave Jones' EEV blog YouTube video on designing your own LCD and then sending it out to China to have it made. So that's what I'm actually going to try to do. The first step, of course, is to determine the specifications of this LCD. So I did some measurements and I actually found the service manual for the PC1. You can find that online. And I've chosen some pages out of it. So here we can see the display tube says that it's an LF8017JE. That is just the number that they have for this custom LCD. By the way, this is not a RadioShack designed product. This is actually a product designed by Sharp. Sharp came out with the PC, I think it's called the 1211, and then RadioShack just rebranded it. So if you find a service manual for the Sharp PC1211, it would be pretty much the exact same thing with the exact same specs. So here we see display tube. That's just a number. Display method, 5x7 dot matrix liquid crystal. It does not mention the custom indicators in there. Display capacity, 24 columns, alphanumerics and symbols. Well, it's 24 of these 5x7 dot matrices. So we have some basic functions, arithmetic functions, editorial functions. That's not the interesting part. This is the interesting part. So there's an overview of the display. Now these displays have some common lines and some rows. So the idea here is that, at least for these matrices, you have h1 through h7 and s1 through s5. And we can see that here is some sort of a counter. And here is, let's see, h8 through h1. Of course, h8 is not going to be used. And this is some internal display buffer. And here are s1 through s40. So these would be the segments. So, of course, you have five of these segments or columns. And you've got 24 of these characters. So, of course, 24 times 5 would be 120. That means that you would essentially need three of these. So the idea is that these are the commons. And then this is the actual data. So what you do is you send out 40 bits of data and then you set up the columns or the rows. Then you send out the other 40 bits of data for the next few characters and you set up the commons and so on and so forth. So here is an example of the actual signals. So they look really freaky. They're not just on and off. They are actually analog voltage levels. So the idea is that you have this hA, which you see over here, is essentially just a clock to clock out the bits. And we can see that you set up s1 and s2. So these are of these things over here. And then you activate the commons one after the other. And then essentially what you do is you flip s1 and s2 and you flip the commons. Now, this is typical of LCDs because you want to drive LCDs with an AC type waveform, not DC. So the idea is that, for example, here we're activating s1 and in this case s2. So we'll drive h5 low and then we'll flip it and then we'll drive h5 high. And of course we're driving s1 and s2 in the opposite polarity. So the overall magnitude of the voltage is the same. It's just that we flip it alternately like this. Now here's an overview of the power supply. And this is where it gets important so that we can finally determine what the specification of our LCD is. We can see that here we have these four batteries. And we've got a protection diode over here. I guess if you put them in the wrong way around. We've got a 100 ohm resistor over here. I suppose to limit the current. The CPU is driven by negative voltage, which says to me that the CPU is probably a PMOS CPU. That doesn't matter. The only reason why it matters is that you have to realize that all voltages are basically negative or ground is actually the most positive voltage supply. You can flip it around so that ground is down here and v-disp is up here. No harm done. Because of course with LCDs it doesn't really matter because the polarity is going to flip back and forth anyway. So we can see here on this side of the power supply that we've got basically just a voltage divider. There's 21.0 k over here. 12.7 k, 12.7 k, and 21.0 k. So we have that being split into va, vm, and vb. And there's a little description here. So v-disp is the low voltage for the common signals, va is the high voltage for the segment signals, vm is some intermediate voltage, and vb is a low voltage. And in fact we have some waveforms over here and some voltages, which is pretty nice. So it says here that v-disp had been precisely adjusted to minus 3.74 volts at 20 degrees Celsius and minus 4.29 at zero Celsius. And it does say that the display should be viewed from a 30 degree angle from vertical. That is actually one of the specifications of an LCD, whether you view it from the top down or from an angle. So we know that we're going to specify our LCD to be displayed at an angle. This is actually called a six o'clock angle, as opposed to a 12 o'clock angle. And Dave Jones goes into that more in his video. So here we see the voltage levels of va, vm, and vb. We also see the timing of these signals, 6.8 milliseconds. And now we know the frequency at which we can drive this LCD. Okay, I realize that I did a little bit of hand waving when it came to the voltages of the LCD. So I just wanted to make some actual practical measurements and go over the voltages. So in the service manual, there is this awful blurry diagram, blurry because whoever did this didn't scan at a very good resolution. We have this printed circuit board, and I've opened up the calculator, and that is this printed circuit board here. And we can see over here that we have a 12.7k resistor, 21k, 21k, and 12.7. So that corresponds to the voltage levels shown in this power supply. So that's this voltage divider here. So that means that the voltage divider is over here. Now, what I've done is I've drawn that out right here. So here was the 21k resistor there in the middle. Here are the 12k or 12.7k resistors, they're on the ends. And I determined that these were connected, these were connected, and these were connected. So we know that these two ends are the two ends of the voltage divider. Now, which end is which? We can see from the schematic that there is a MOSFET over here whose one terminal is connected to the V-disp end of the resistor divider. So all I have to do is find that MOSFET and find out where the connection is. And indeed, I found that the MOSFET is actually right here. And looking at that, I determined that this leg of this resistor was ground. That's why there are all these scratchouts because I made a few mistakes. So then what I did was I simply turned the calculator on and measured the various voltages. So we know that this is ground, this is negative .89, that corresponds to VA. Then we get Vm, which is the medium voltage, minus 1.95. Then we get Vb, which is minus 3.00, pretty much almost exactly. And then we have Vdisp, which is minus 3.89. So the interesting thing is that Vm is almost right between 0 and minus 3.89, as to be expected, because this is symmetrical. So that's one thing settled. The next thing that we have to look at is the diagram of the LCD waveforms. So we have these S's over here, and we have these H's over here. Now, these correspond to the two electrodes. These are actually just commons, and these are segments. Doesn't really matter. The point is that we want to know what the voltage between the segment and the common is. And over here on the side we see the different voltage levels. So the common goes between ground, VA, Vb, and Vdisp. And the segment goes between VA, Vm, and Vb. So I redrew that diagram here. Here is the common, and here is the segment. So for the segment to be on, that's this pulse here and this pulse here. Remember that this is AC, so we want to see this swapping between voltages. So ordinarily the segment just remains at Vm, right in the middle of the range. But to activate, we go to VA during one half of the cycle, and Vb during the other half of the cycle. Now, also in order to turn the segment on, the common has to go all the way down to Vdisp, so apparently it remains during one half of the cycle. Let's show the cycles right here. So this is one half of the cycle, and this is the other half of the cycle. So during one half of the cycle, the common remains at VA, and during the other half of the cycle, the common remains at Vb, except when you activate the segment, in which case the common goes down to Vdisp or up to ground. So let's see what the difference in voltages is. So right over here, this is when the segment is going to be on. So the difference between these voltages is going to be VA, which is 0.89, minus negative 3.89, 3 volts. And likewise, we should also have, on the other half of the cycle, probably minus 3, right? So we're going between Vb, which is minus 3, and ground. So that's obviously minus 3 volts. Now, what happens when the segment is off, so say right over here, or even right over here. So here we have 0.89 volts minus minus 0.89 volts, which is 0. Similarly over here, we're going to have minus 3, minus negative 3, or minus 3 plus 3, or 0. And when we have, say, the common is not active, and the segment is not active, so we have Vm minus 1.9 minus minus 0.89. So minus 1.95 plus 0.89 is, what is that? Is minus 1. So let's just call that minus 1 volt. And on the other side, of course, we're going to get right over here. So this is minus 1.95 plus 3. So that's also about 1.1 volt. So from this, we can see that, first of all, the segment's going to be off with plus or minus 1 volt. The segment's going to be on with plus or minus 3 volts, an AC voltage of about 6 volts. Now, I chose 5.2 because I think I chose these V-disps to be slightly less. So interestingly, this says minus 3.9 volts right over here, which is pretty much what we found. So this is actually a well-tuned machine, a well-tuned computer, but you can see that the voltage can vary between 4.29 and 3.27 at the high end. So what I did was I actually took, I believe, the 3.27 volts and calculated this out to 5.2 volts. So that's sort of the minimum voltage required. So here's this minus 3 to plus 3 wave form. Here is the 6 volts between them. So that's with a V-disp of minus 3.9 or minus 3.89, whatever I measured. So again, the 5.2 volts is going to be the minimum. So there's also a threshold. Now, you can see here that the segment really needs to remain off when you apply plus or minus 1 volt. So of course, that's going to be a wave form that looks like this, minus 1 to plus 1, which means that in terms of an AC wave form, you're going to get 2 volts. So obviously, the threshold has to be somewhere between 2 volts and 6 volts. And of course, if this is 5.2, then you definitely want the threshold to be below 5.2 volts. So again, this is the minimum. You want the threshold to be somewhere between. And that's why when I wrote my specification, I put down a power supply of 5.2 volts. Now, you can apply more and that will just mean that the display is going to be a little bit stronger. So the bias of 1 third, again, that referred to how many different voltages you had over here. And then the duty cycle is just during each half cycle, each segment is going to be on for 1 seventh of the time. And then the final thing is the frequency, which is 288 hertz. And that, I believe, came from this 6.8 milliseconds time. So we can see that VA flips between negative and ground. So where is VA? Right here. Now, when they're talking about this VA, they're not actually talking about these voltage levels. They're talking about sort of like a logical VA, which actually flips between, I think, this and this. I'm not sure about that. But in any case, the point is that each cycle lasts 6.8 milliseconds. So when you do the math, that turns out, I believe, to be 288 hertz, which is important because with a duty cycle of 1 seventh and a frequency of 288 hertz, which is 6.8 milliseconds or so, actually, let's divide that by 2 because that's going to be the half cycle. So it's 3.4 milliseconds. So the half cycle is 3.4 milliseconds and a segment is only going to be on for 1 seventh of that. So 3.4 milliseconds divided by 7. But it's about 500 microseconds or 0.5 milliseconds. Now that's interesting because there was 0.5 milliseconds mentioned here as the basic clock cycle, 0.5 milliseconds. So that seems to bear things out. So in other words, the manufacturer is going to have to choose the liquid crystal so that it will turn black if you apply a signal with only 500 microseconds, one way and then a delay and then 500 microseconds another way. And that's why it's important to specify both the duty cycle and the frequency and the power supply and the bias tell the manufacturer what the threshold is supposed to be and how you're going to drive the pins themselves. So this should be a full specification. So anyway, we have some voltage specifications and from that and from viewing the LCD under a microscope very carefully and tilting it to make sure that I could find the electrodes, I was able to come out with a specification just like Dave Jones did. So I did this in Inkscape and then converted it to a PDF. So here we have the measurements of the LCD and I think this should be pretty much one to one. So it measures 128 millimeters along the long side and 23.8 millimeters along the short side. This is made out of two pieces of glass. So hopefully you can see the two pieces of glass. One piece is smaller than the other and the reason for that is that the pins are the electrodes along this side. Now in Dave Jones' video he has pins, actual physical pins attached to those electrodes. The TRS-80 pocket computer uses these elastomeric connectors and elastomeric connectors are essentially bits of rubber with conductors that run along this sort of angle and they're isolated from each other. So all you really have to do is place the elastomeric strip on the electrodes and then press it up against the printed circuit board and here's one of the computers that I took apart. You can see that basically these are just bare pads. The elastomeric strip goes up against those pads, up against the electrodes and then this bezel actually has these tabs that go through the PCB and then you twist it to tighten it down and that basically squeezes the elastomeric strip up against the electrodes and the pads and because the pitch of the conductors in the elastomeric strip is quite fine, it doesn't really matter how you move the elastomeric strip. If you move it a little bit it's still fine. The key though is to get the electrode centered on the pad when you put it down. So that's why over here I specified connection method elastomeric because when I send this to a factory in China I don't want them to supply pins, I just want them to supply just the bare glass basically. We can see that I wrote down the dimensions so there's a physical area that's there's also a display area. Now the display area is the area where the liquid crystal is going to be placed. So the display area obviously obviously isn't going to fill the entire glass because there are some crossing connections and you don't want those to be display segments. So the display area is going to be limited inside and I think but I'm not sure that there is some sort of I don't know what it is. It's some sort of a well that goes around here that contains the liquid crystal. So I was able to determine what the pin pitch of the electrodes are. Interestingly enough the pin pitch at the bottom is not the same as the pin pitch on the top. At the bottom it's 1.6 millimeters, at the top it's 1.8 millimeters. I don't know why. There are 144 pads, 80 on the bottom, and the rest is on the top. These are the 24 by 1 characters. Each character is 5 by 7 and these are the custom indicators shift, degrees, radians, gradients, depth I think for define, run, program, reserve, and the activity dot. Now the thickness of this glass it appeared to me to be 1 millimeter, however 1.1 is standard so I spec this out at 1.1 millimeters for the glass. The total width was 2 millimeters so I may actually be causing myself a problem because twice 1.1 is 2.2 and then there's actually a tiny spacer in between to make room for the liquid crystal. So it's going to turn out that this is probably more than 2.2 millimeters which may cause a problem with this thing because once I put the glass into this compression housing bezel thing will I be able to tighten it down? I hope so. So let's see. What else do we have? Okay so I also specified the sizes of the dot matrix. Each of these dots is 0.6 by 0.6 millimeters. Now I did specify plus or minus 0.1. The reason I did that is that well first of all good mechanical drawings always have a plus or minus on them because you're never going to get anything exact right? What does 0.6 millimeters mean? Does it mean 0.600000 millimeters down to infinity? Well that would be infinite precision and you don't have that with machines. So I always found it useful to specify some sort of an accuracy or precision precision number so that the manufacturer can know whether they're capable of manufacturing one of these things. Alright so this is the layout. I determined that each of these matrices is 4.6 millimeters apart. Now the total is 105.8 millimeters. That's the crucial dimension because if you were to specify 4.6 millimeters plus or minus 0.1 then by the time you get out to 24 characters that turns out to be plus or minus 2.4 millimeters. That's not what you want. You want the total dimension to be this precise. So that's why this actually doesn't have a precision plus or minus number on it because that is a calculated number rather than a specified number. So the specification is actually this over here. Let's see. I specified how far down from the edge this is from each edge. I specified the height of the indicators. Now when you get to the indicators the problem is what font do you use? Well you know really the best that I could do is specify a font that was close enough. The closest font that I could find was deja vu sans bold semi condensed. So the nice thing is that that's a freely available font so the factory can just slap that down and use it. I still had to specify the length of the indicator right because some of them will be you know maybe shorter than the other because this isn't obviously the font that they used. This is a modern font. This was probably I don't know some sort of a custom font that they used. So you want to specify where the indicator sits the length of the indicator and then you want to specify all the pad connections. So what I did was I just put this under my inspection microscope traced out all the electrodes it wasn't that hard and I determined where the pads connect. So we can see that the indicators actually have two commons. One of them is an indicator common that connects to seven of the indicators and one of the other commons for these rows is reused for let's see it's def and the little indicator the little round indicator that I just called dp. That usually stands for decimal point. So here we have basically the title the part number. I made it the same part number as the custom one that appears in the service manual. It's a 24 by 1 character display with nine indicators. I revised this on February 5th. Always a good idea to put a last revised date on it so that when you make the inevitable change you update the last revised and that way you can always say use the revision of February 5th instead of February 1st and if it doesn't match then they're gonna you know raise a flag. Dimensions okay display mode positive that basically means that you're going to get black dots on a gray background as opposed to gray dots on a black background that would be negative. So display mode is positive the display type is reflective as I explained before the color is monochrome black on white originally I had this saying black black and white and one of the suppliers came back and said you specified a positive display mode but black and white is negative. Do you mean black on white? So I said sure okay I mean black on white. There is a language barrier and you have to work around that. The viewing angle is six o'clock also known as bottom the connection method is elastomeric. The operating temperature I think I took that straight from the service manual or the specs from the user guide the calculator is specified the computer is specified from 0 to 40 so that would be the operating temperature. So this is my specification what I did was I went on to Alibaba and I just chose some manufacturers that seemed like they were interested in making custom LCDs and I sent them this. I also to make it easier on them I went into kikad and I reproduced the electrode layout because normally what would happen is if you just send them a specification like this and you didn't care how it was laid out they would lay it out however they want and that takes time and therefore costs money but if you were to just give them a gerber containing the electrode layout well then they could just use the gerber and convert it to whatever format they use and then just run their process. There's still some tooling that has to be done obviously you have to cut the glass to the right size you have to place the glass into a jig you have to make the transparencies and all that goes into the tooling costs but also what goes into the tooling costs is the design time. So I decided to short circuit that by actually providing them gerbers and saying hey look I've designed this for you you can redraw this if you want but that's up to you. So anyway I sent this to about five different manufacturers some of them got back because they completely did not understand the sheet which is fine I just said well thank you but no thank you because obviously if they can't work from a drawing like this which is a full specification then they're probably going to make a lot of mistakes. Some of them got back saying well okay we can do this but the minimum order quantity is three thousand. Now there aren't three thousand of these things in the wild you know at most there's probably only a few hundred so I said well thanks but I'm looking for an order of maybe 200 of these so some of them said no one of them actually said yes and the price that I got was about 300 dollars for the tooling which includes 10 samples so the idea is that you go back and forth with them to make sure that the diagram that they put together is correct because obviously you don't want to lose anything in translation once you say yes that looks good they will go ahead and tool it up and manufacture 10 samples and that costs 300 dollars. Now after that it's really uncool to say thanks Sia because really they priced it out so that they want the minimum order now the minimum order was 500 dollars for 200 LCDs so you do the math and that's $2.50 per one of these that's actually pretty good now obviously when sharp manufactured these they probably got these by the thousands and they were probably able to pay well you know let's talk about today's dollars you know maybe a dollar a piece or less but of course with such low quantities it's obviously going to be a higher cost so all told I would have to pay about 800 dollars to get 200 of these manufactured so that's about four dollars a piece say now if somebody has one of these I'm kind of hoping that they would be willing to pay well over four dollars you know let's say 10 dollars right because you want to go about two and a half times your cost so I'm kind of hoping that they would be able to pay 10 dollars just to get a replacement then they just you know remove it put it put it in and it's done that's the hope that is probably not a viable option because again like I said there's probably not that many in the wild and there's probably very few people who actually want to fix these up to make them new so in the end I'm going to spend 800 dollars to get 200 of these I'm probably only going to be able to use well however many of these I can find on eBay let's suppose you know that that it's like you know 10 or 20 maybe so in effect 800 you know using 20 of them that's about 40 dollars for each of these where you can pick these up for five dollars can I resell these actually working with new LCDs for 40 dollars I don't know but you know this is an exercise to see how I can do this now another exercise that I'm actually going to do is can we make these from scratch now I know that Ben Krasnow has tried to make LCDs he made a one segment LCD that's nice but I'm looking for you know commercial quality so well you can go to China and just spec it out and have it made for you and then have way more than you need or you can probably spend about half that much and get maybe one or two so you don't get the economy of scale but the question is is it even possible so that's going to be another series of videos so I think that when we come back we will see the samples that I get and see if they actually work in one of these known working devices