Hi just gonna do a quick video taking a look at an issue that some people have had with the Eevblog. be M23 five multimeter and that is the viewing angle of the LCD. So I've got three other meters here just you know, randomly chosen and you might notice that the eevblog meter is just fine. There's nothing wrong with it, in fact, it well don't know if this will sharp on camera, but it's probably the best of the bunch at this particular angle.

The digits are nice and fat look at that and it seems to have pretty good display contrast. And if I take it directly overhead like this - and you can see, it's still pretty damn good. In fact, you could say it's probably the best out of those, right? So what's the problem? Well, the problem has to do with the angle of the light. and I actually just did that previous shot with not all of my studio lights turned on here.

So I'll just repeat it with the lights turned on all of them and you can see. It's exactly the same excellent result for the BM 235. So these are all of my studio lights here and you'll notice that I actually have them over the center walkway like this. I've got my bench here that I do most of my you know, tear downs and other main shots on and then I've got the mailbag, a bench over here that yes, the labs in a state of flux at the moment so to speak.

So these lights are angled down like that. There are no lights up above here. there was an existing one, but they're not turned on so there's no light source coming from behind or on top. And let's call that the from the top of the LCD they're coming from the bottom of the LCD.

The angle of the light comes in like that. then the BM 2, 3 5 is an absolute winner. But let's look at what happens if I have the lights coming down at an angle like this onto the meter so they're coming from the top instead of the bottom. the glare so that's really quite annoying.

But as you can see, it's still doing a reasonable job. Reasonable job, reasonable job. until you get like on top of it might start see them starting to fade out coming down the lights, probably directly on to the LCD like that. and then if I stand it up so they're straight vertically like that.

So the lights coming down from the angled from the top you can see the BM, Two Three five starts to fade out a bit, but they're probably equally as bad at you know, a really bad angle like that. And if you compare it with the BM Two Five Seven which is an older model, the Two Three Five hasn't replaced it, but it is a much newer model than you can see that the new Two Three Five actually does you know fade out a bit more so of course LCDs Displays like these have a polarizing filter on the front of them and we'll actually see significant differences in here. So I've got a polarizing filter on the front of my camera here and you can already start to see that the EEV blog is doing something funny. The other two, you look reasonably fine.

If I start to turn the polarizing filter, you'll notice that the other two like completely vanish. You can see the display is black, but you can still see the Eevblog LCD but it sort of changes that might have a function. Looks to be some function of the curves display at play there. That's rather interesting.

It doesn't work exactly the same as the other two. This is certainly not just a Bremen thing. I've got two key sides here. One of them is branded Agilent and you'll notice that the new Ru 1282, a keysight here does has a very similar result to the Broman's but it's just interesting that they must be different polarizing filters between those you know, you put the Uni T back there and the Fluke 17b and it just goes wham-o black.

Like that, it is significantly different result. So they've obviously some type of different polarizing filter in them. Just thought I'd show that it's interesting. So let's have a look at the LCD module here.

It just pops out after you get the board out. If we have a look at the parts inside here, there's just a backing plate holder. There's a diffuser for the LED backlight. You can see that there's three LEDs in there and that just go into the cider.

here. it's just using it as a light Piper basically to get the even backlight on the thing. And then we have the LCD itself. That's the flexible zebra strip there.

It's got just multiple conductors in there, carbon carbon conductors that transfer the contacts over to. It's just a rubber strip. It just peels off and as you can see, there is no other layer in there at all. There's no, you know, the polarized layer or anything like that.

It's all built into the glass, so it's not like we can sort of, you know, take something out or anything like that. Now, some people saying that the curved nature of this display causes an issue. and it does. But hey, you know, the Fluke 17b, for example, has a similar sort of reflection issue with the curved display like that.

So yeah, it is a problem. but that's not the cause of our contrast issue. There are two things that are going to cause a contrast issue in here. One is the actual physical manufacture and design and filtering on the LCD itself, and the other is the contrast bias voltage that you actually apply to the LCD.

And just in case you're wondering, there are different types of LCDs. There are reflective types that don't have a backlight and they will have a completely mirrored silverback on them. This is not one. This one's what's called a transflective one and or trans reflective one.

And and because it's got to have the backlight, the backlight has to get through like that. It's got to be able to shine through. So it's part reflective and part transparent. So there's obviously nothing we can do physically to the LCD light.

Replace the filter, or you know, change it or remove it or anything like that. So we now have to go look at the bias voltage to the LCD itself. So let's go to Dave CAD here for a second because that's important. Understand the difference between viewing angle and bias angle.

They're two different things and let me try and explain this. We've got our LCD here. Okay, then we've got our perpendicular axis right smack in the middle like this. Now when they design an LCD it's going to have a you a certain viewing angle like that.

Okay, so that in there will be the viewing angle that might be I don't know 90 degrees or whatever it is And that is the viewing angle where you can view it anywhere with inside that plane and it's going to be acceptable. It's not just going to suddenly vanish when you get outside. You've got to pick an acceptability point. Now that is viewing angle and that is designed into the LCD material itself.

In terms of what liquid crystal materials that they actually use, I Just realize I still have my polarizing filter on there. There it is that's better and what type of liquid crystal they use in there and the chemicals and everything else. It a complex LCD manufacturing technology, so that's viewing angle and but that will not change when you adjust the bias contrast voltage. You might be familiar with this.

A product might have it, you know, a knob on it for example. Or it might have a software control that can that changes the contrast of your LCD You no doubt familiar with this and it changes the bias voltage to the LCD. Now it's important to understand that bias voltage does not change this viewing angle. Here all that changes is the bias angle.

So the LCD will always have this fixed viewing angle like this. What the bias angle does is it actually rotates the viewing angle like this depending on how you want it so you can adjust that bias voltage and that's effectively what it's doing is changing that fixed viewing angle. So if you want your product to work from the low side like this, the bottom side of the LCD you want better. You know you've got the you meter laying flat on the bench like this and you want to be able to see it at an angle.

Then you want to adjust your bias voltage so that you get and you know so that you get the best viewing down at the bottom angle. So that's all that that bias voltage does. And of course, the Eevblog meter is no different. It has.

well, it does not have an adjustment for the Weisse bias voltage, but it has a resistor in there which fixes the bias voltage at a particular point that Bremen determined was acceptable. and I don't think it necessarily is I Don't think they've optimized it enough. And sometimes the bias angle is specified in degrees And what that is is if you take the center line, the center mark of the viewing angle here, then the bias angle is the angle between the perpendicular plane of the LCD Like that, up to the center of the the middle point of the viewing angle. like that.

So that'll be the bias angle in degrees. and the backlight actually tends to have a worsening effect on that display angle too. I Mean it. That's just yeah.

Pretty bad. So there you go. So Brahman Have investigated this and they've said that the bias resistor is actually our 67, which is that one right there? Little Oh, six, Oh, three. Job.

Luckily it is accessible on the top side here so you don't have to take the entire board out if you want to change it. But anyway, that one right? There are 67 currently Twelve Point, Seven, K but they said they have selected values of seven point, A, 17, point, Eight, K, and twenty One Point Five K before. but they settled on Twelve Point Seven case. I'm going to change that.

So what I've done is soldered two wires onto there and we can feed that out the case because the battery terminals go our spring terminals onto there. So I have to put the back case on to pair it up. So I get some wires out, go to our deck. a resistance box? No worries.

So let's switch this back on and I've got it. Not connected to anything, just flapping around in the breeze. And today I Look at that super contrast. Yeah, Black as the Ace of Spades that is.

But we can see the ghosting on here. and ghosting is where it basically turns on or partially turns on. The other segments just appear to be on like that. So that is.

Yeah, that's not great. Obviously, even when you bring it up like that, you can still get ghosting down there. so a contrast far too high. Okay, so let's just start from the minimum angle here coming down from the bottom of the LCD and the weights from the bottom as well.

That's where we're seeing the ghost in. Typically, when you're set in contrast like this, you want to set it for your best possible viewing angle and then just get rid of the ghosting. So I've got a hundred K at the moment. so let's actually drop that down to 10 K and see what we get.

Bingo it's gone. so that's what we're getting. that's would have been the level that we're getting before the 12 K level. so let's actually go up to 20 K You can see that there is very significant differences I've got fixed exposure on the camera so that's hoping on that's turning up I can really see a big difference in there.

so their recommended value was 21.5 K or whatever. 17 K they well I could do 17 but yeah I reckon like 20 K does the business. no worries. And then if we go back to our original setup where the light is coming from the top and we're also looking slightly down from the top as well so you can see the BM 2, 5, 7 and the new one, much better beauty.

Yeah it makes a hell of a difference. Look, this is the original one and this is our 20 K1 modified if we go to like 30 K so you can switch in here and really see it. 10 K that's 20 10 20. But ultimately the bias angle can change with temperature on these things.

So to engineer this solution properly you would cycle this over temperature and determine you know over the typical operating range, determine the best value and things like that. But yeah I think they've just chosen a to lower value here I think that should be 20 K in there instead of the 12.5 that they're putting this thing and quite a few people have mentioned this. not everyone because it depends on your light condition and everything like that. So I guess they didn't I don't know what their temperature is over there I don't know what their light conditions were when they were.

you know, obviously they had people sit around deciding on what you know which contrast looks better. It's a like a subjective thing and if don't take into account angles of that not only the viewing angle of the person looking at it but also the angle of the light come into it then it can make a big difference anyway. I hope you found that interesting I'm not going to thermally cycle this thing or anything like that now, but yeah it looks I'm gonna feed this back to our Bremen and I probably think they should at least start change it to 20k because I can't see by doing that I can't see any significant ghosting, but hey, you might get ghosts in a different temperature. who knows.

Anyway, if you enjoyed that, please give it a big thumbs up. As always links to the forum and to discuss it and YouTube comments and blog website. Well what sort of chess catch you next time? Hi, it's engineering terminology time. We're gonna talk about orders of magnitude and you hear me say it all the time.

Not just me, but it's a very common term in electronics and other engineering and science for that matter. Order of Magnitude. Exactly. What does it mean? You hear me use it in terms of I was out by an order of magnitude.

or that was an order of magnitude bigger than I Thought: Or it's dropped. Something's dropped by an order of magnitude.