Hi I've done a video quite a long time ago. uh called Solar Power Hope where I looked at uh solar cells and did some measurements because I was looking at developing a solar powered uh calculator. but as it turns out, these piss a little. uh.

solar cells. even the best ones on the market most efficient ones on the market could not uh, you know, generate the required current that I needed for the dot matrix display and things and I just uh, got curious. Did measurements on the solar cell itself but I never did any measurements on these solar powerered calculators and how much current they actually draw. So I thought that might be interesting.

So I thought we take a representative example. a fairly uh, recent one in uh, terms of uh, these types of casos. it's the Prev Vpam rubbish. Of course it's the FX 260 solar.

It goes under other uh uh part numbers as well I believe in different countries, but this one is fairly recent I don't know, it's probably five or 6 years old. They might even still sell it in places. and I thought we just crack this thing open and uh, have a look at it because the So it's obviously got a big cap in it. Check it out, see if I cover that solar cell up.

There's obviously a big electrolytic cap in there or something holding on the charge there for quite some time and even when they display blanks like that still still keeps it, it's still in there. So I thought we'd actually crack this thing open and do some measurements and see the actual current consumption. Uh, both. uh, static display and also, uh, during calculation if we're able to, uh, probe it.

But I've got lots of calculators. If we can't easily probe this one, sure we can probe another. Let's give it a go. and here it is: Tada Look at that.

We've just got a uh chip on board. classic black blob. there. they've got the epoxy coding on that.

Uh, these casos. um, many different construction techniques. I might even take another one apart later. And uh, show you like a you know, a be diey approach or something like that.

And there's our solar cell. It's a Sano Sa51 54 and uh, there's not much else in there. There's the electrolytic uh cap. Of course.

that was fairly obvious that it had a large size cap in there and all got is two other surface mount ceramic caps and that's it. I Mean you know there's no Crystal no, nothing in this thing. obviously a built-in uh, um, RC oscillator in this thing, it would only be running at you know, tens of KZ or something like that at most. This thing, of course, is not particularly fast.

Let's do something and probably the most complex thing this thing can do. Let's do 69 factorial, shall we? at 69 cuz that's the upper limit of 99 exponent and you can. Ah no, it did it reasonbly quickly. I've got slower ones than that, but yeah, anyway, it's not a particularly fast machine incidentally.

let's see if that's any slower if we lower that voltage. so the LCD dims. It's really quite dim now, so let's do that. 69.

You can just see it and no, it's probably about the same amount of time I think think so. Looks like voltage has no effect on the Uh speed. It might have a slight effect maybe um, because of the RC oscillator in the thing, but yeah, probably not much. But anyway, um, the good thing about this one is that we can just crack straight into there and uh, uh Power this thing from a bench Supply see where it see what operational voltage range it runs over and also measure the current and uh, we'll do that.

Uh, we'll also take out the Uh Supply cap as well CU We don't want that, um, interfering with our pulse Uh current measurements. Okay, this is the test setup I've got here. I've got my microcurrent of course. Classic.

uh example for the use of this: I Got it on the Uh microamp range. so it's going to give out 1 molt per microamp. so I've got the output of that going in to the new agilant U1 1273 Ax, You haven't seen this Uh meter before. It is a Nei Um, it's basically exactly the same as U uh 1273 but it's and with the OLED uh, this very sexy OLED display on it.

but it's designed to go down to minus 40 or something like that H that's its only Advantage Anyway, go figure. but the OLED display is sexy. You probably see some flicker there due to the uh uh frame rate of the video. Anyway, that's measuring the uh current, uh drawer of the thing I've got it powered from a bench uh power supply and and the Fluke 87 here is going to measure the Uh input voltage at the moment I'm actually measuring the Uh solar cell voltage.

So it's um, 2.62 uh volts there. You know, if I put my hand over it a little bit drops to 2.5 so it looks like you know two? I've got like a th000 lux here on the bench. so um, looks like 2.6 is you know, the maximum? You maybe you might get a bit higher than that. you know, out in direct sun when you're talking tens of thousands of Lu or something.

But indoor environment here about 2.6 Vol So we know it. uh operates from, you know, 2.6 downwards. So we'll uh, start around there on our power supply and drop it until it dies. So here we go.

I Got the power supply set to 2.55 volts. It's not measuring the Uh solar cell anymore, it's measuring the bench Supply input and uh, of course it's working. just hunky dory and uh, we're getting it's drawing about uh, three. just over three microamp.

So I don't know I Kind of expected it to be a little bit less than that. This thing has an auto diming mode. You got to turn it on to get the real sexy bright OLED does that to save power consumption I Guess Um, now it's working just fine. So let's drop this sucker bench.

Supply Here until the uh calculator. We're viewing it sort of almost straight on, maybe a bit above angle, but it's certainly still excellent contrast on that. LCD at 1.25 it sort of starts to drop it. yeah, say about 1.

Point Ah yeah, if you view it down on a lower angle down here, yeah, you can. Oh, it's probably it looks better on camera here, but uh, there you go. Let's drop it down a bit further. and uh, it certainly is still usable down to 1.

Vol Oh yeah, M If you, you can't see it on the screen, scen there. but if you raise the angle there, you can just see it. So it's barely usable at a volt and it you know under that it's just completely dead. But at a volt? Um, we're getting about 1.4 microamps and so.

but let's take it back up to two, for example. So 1.4 to 2.6 There's not a huge difference in the operational current there, so let's see what happens when we press a key. Let's see the current. There we go.

it does jump up hard to well. I Can set the Uh Peak mode on this and see if we can capture the peak of this. There we go, it's beeping away at us, so let's capture. Yeah, there we go.

It's peeking at like five six. It's yeah, let's try 69 Factorial: Wa there we go. When it was doing that, factorial jumped up to 16.2 microamps. Oh what a Whopper let's try that at 2 and 1/2 volts or thereabouts.

69 Factorial: Yeah, yeah no, it's pretty much 162 is where it's going to Peak Let's uh, zero that out and let's do it again. 69 Factorial: Boom. Let's see what happens when it's say doing a uh doing a log here. let's do I don't know the log of.

Let's do the log of 42. There we go. 10.5 so it's not as high as the uh factorial one there. and if we do say Square t of 42, this is a good use for the min max mode on your uh multimeter.

you can c capture these Peaks cuz it is quite capable of uh, getting those Peaks Now it does a square root really quickly so there's not much uh peak in there. It takes more to do the log. so we go 40 42 log. There we go.

Yeah, it definitely takes more current to do a log than it does a square root. and if you watch it closely, you can. Actually, when I press a key, you might be able to see it capture. uh, sort of transition up there on the bar graph there cuz the bar graph updates much faster than the display does.

So there you go. Interesting. And because the other one doesn't uh, switch off because it's there's no battery and it's solar powered only there's no off function I can't measure the standby current consumption so I thought I'd get this: Uh, Tandy EC 414 Um, it's a rebadge Casio of course I'm not sure of the Casio model number off the top of my head and when it's on, it's drawing at about 3.8 microamps and when it's off, let me, rather than wait for the timeout, I'll just switch the damn thing off. and uh, so let's switch down to the micro amp range sorry the Nano amp range and uh, move this up a bit.

There we go: 700, just over 700 Nano amps and if you're curious to see inside this one, it's just a quad flat pack. very traditional construction with uh, some axial diod there actually uh, hand soldered on and once again, that's about it. nothing else. And this is of course a dual power solar battery version.

So we got our solar still up there and also the battery connection and I did promise you one with different construction and I know that this one cuz I took it apart when I first got it of course back in a probably 1987 I think I got this one. These are about the same vintage got this one a year or two possibly before that. Um so this is you know about 87, possibly 88 Vintage at most and it's the Uh Tandy EC 431 and I know this one has different to even though it's the Um practically the same age as this one which had the quad flat pack. this one has radically different uh Chip Construction in there.

so let's take a look there it is. Check it out! I will get the macro lens out and have a good closeup of that, but it is radically different to the quad flat pack we saw before. and check out this uh flat Flex on here which has these two diodes can I I'm not sure if I can peel that all the way back. Oh yeah, why not.

Anyway, there we go. look at that. They got a flat Flex in there just to mount those two diodes on. Very, very interesting.

So you can see that there's no PCB in this thing I Guess they were uh, experimenting with uh, what cost savings they could get with no PCB and they've gone. You know, the complete flat Flex rout CU They knew they had to mount the two uh dodes on there so they decided to uh Mount them sold them directly to the flat Flex bonded on and well look at that. nothing I mean the battery contacts down in there, it's just got your Tra. It's just got the flat Flex membrane down in there under the battery.

for the lower battery. contact some of that's actually worn off by the looks of it and check that out. that is obviously the bottom of the D there and they've uh, flipped it over and mounted it on the other side because it's clearly the bottom because you can't see the uh circuitry on the top of that. the actual you know the circuitry etched into the Silicon wafer.

So it is. It is very interesting. I'll see if I can lift this membrane out of here and try and have a look at the other side of that. Here we go.

let's have a look at this. Check that out. Isn't that? absolutely fascinating? Little bubbles in there. They almost look like little vas or something, but they clearly aren't That's just uh, something trapped underneath the bottom of the chip there.

But you can see the individual wires sort of. you know, like a kind of like bonding out from the chip. but they aren't actually Bond wires. They're actually impregnated into the plastic film there.

So they've got a two layer construction on that. They've got this very they've got this uh, actually, that is. that's not yeah, Yeah, it's flexible. It's flexible so that is a bit of more rigid type of plastic.

So they've got that, which is what they mount the chip on and they so they flip it over and looks like they do actually solder it down to these very fine pitch I'm not sure that pitches in there, but it's absolutely incredibly fine I'm sure and then these come out to the pads along here which then this is bonded to so that thicker plastic there is then bonded onto your traditional uh, carbon based membrane there. Absolutely fascinating. If anyone knows what this construction technique is called and or if it's still use these days, please, uh, leave it in the comments or jump on over to the Forum to uh, let us know because it really is fascinating. So I wonder if this is like something CIO were experimenting with at the time and whether or not they still use it? I'm not not entirely sure, but there you go.

That is only like a year or two difference between that other Tandy one we saw before and this model which in the other one before just used a standard PCB and a quad flat pack and this one radically different. Absolutely fascinating. So there you have it for this particular Casio FX 260 Solar Calculator Current draw ranges from you know, in the order of 2 microamps up to uh 15 or 16 microamps. so I expected.

Uh, a bit less than that actually. I'm a little bit surprised that it draws that much, but go figure. Anyway, little experiment I Thought: I'd share. Catch you next time.