Hi What if you wanted to design a better multimeter? Not one in terms of features, but in one in terms of lower Burden Voltage. Now I've mentioned Burden Voltage before. I've even designed a product to overcome Burden voltage limitations on a multimeter. It's the microcurrent you've seen many times.

I've mentioned it and had it in many videos. I've even written a whole article on the project and Burden Voltage and what it is and how it's a problem. So click here or down below somewhere to check that one out. So I Thought: we take a look at a typical multimeter current measurement front end and see if we can actually redesign it so that we get improved.

Burdon Voltage Performance: There could be a few traps in this may not be as easy as you think, so let's go. So what I've got here is actually a typical multimeter front end for the current measurement inputs. So we've got our milliamp, some micro amps shared. Jack That's fairly typical for a multimeter.

probably the majority out there have them are shared and then they have a separate amps jack as well and of course, the ground jack here. We're not worried about the positive voltage input for voltage and resistance and and all the other measurements that's actually an entirely separate circuit. Effectively, they might even have like a big isolation slot on the PC physical isolation slot on the PCB itself to actually separate the two sections. So we're not interested in any of that, just the current measurement capability because that's where Burden Voltage is a problem.

Just a quick recap: Burden voltage as the voltage dropped across your multimeter across the terminals of your multimeter when you measure current. And it's to do with these internal current shunt resistors that are used are their their resistors. So when you pass current through, they drop voltage and in many cases this can be a very significant voltage. It could be in the order of hundreds of millivolts or even several volts drop.

And if you're trying to measure, measure the current and say a 3.3 volt circuit and your multimeters actually drop in a volt or even half a volt. That can cause real big problems in your circuit, so that's why we want to minimize it. So typical multimeter front-end looks exactly like this and we've got our amps jack here. it goes through the hey.

Joseph use 10 or 11 or 15 amps sometimes. High rupture capacity fuse designed to fail. Really safe with high surge overloads and they're typically rated at a thousand volts because that have. Otherwise, if they're to lower voltage some of the cheap multimeters they might be HRC fuses, but they might not be raided.

a thousand volts or maybe 250 volts or something like that. So they're not nearly as safe as the thousand volt ones which are designed to stop arc over and stuff like that. Anyway, that goes in. it goes into a current shunt resistor here.

In this case, it's ten milli ohms or zero r01 if you haven't seen that terminology before, I Could have written this as point Zero one Ohms like that, but it's typical to replace the decimal point with the are like that. It's just common terminology you don't need to be are confuse, just understand it. So that's what we're going to use here. So Ten Milli Ohms current shunt resistor for the Amps range.

Almost every multimeter out there is going to use a Ten Milli Ohm shunt. And you've seen these if you open up a multimeter that it's typically a like a little bent out wire that's like Nichrome or Souther, some other lower temperature coefficient art metal that they use to form the current shunt. There's a few multimeters real high priced, high quality ones on the market that might use a proper SMD current shunt for example, a four terminal one. but most multimeters on the market just use a micro ohm resistance wire because a they're very high power B They're cheap and they just do the job.

Now of course you've got to sense the voltage on that, so that's why I've shown these two sense terminals. that's a four wire sense terminal measurement and I won't go over that. Why I've done that in separate videos I'm sure, but because it's such a low value resistance, Ten Milli Ohms, all of your PCB trace resistance can cause a problem, so if you're not sensing the voltage directly across the current shunt terminal, then it can cause issues. Yes, you can.

Our software calibrate that out of your with your multimeter calibration, but typically the copper on your PCB is a different temperature coefficient to the your current shunt resistor and it can get all messy and changes with temperature and stuff like that. so you really need to sense that and a well-designed multimeter will do just that. Now your milliamp and micro amp jack typically shared up here gets a little bit more complicated. It does go through a fuse just like down here, but a lower rated one.

Once again, it's high rupture capacity HIC but a lower value typically like 600 milliamps for example, for a 500 milliamp maximum current range. Once again, thousand volts for that arc over protection. And then generally they're going to have a diode bridge to actually clamp that voltage across the current shunt resistor. and they'll typically have that directly here.

So you've no doubt seen diode bridges are before and this is a typical surface mount package. might be the DF 10 s for example, and these are going to be rated in a thousand volts. Now, they don't always use a diode bridge like this. You might open up your multimeter.

You might find that they're using our four, sometimes five, or six our diodes in various configurations, usually a bridge configuration to actually clamp the voltage across to protect your current shunt resistors inside. Because if you accidentally use your multimeter incorrectly and put a voltage across here, then it's going to be presented straight across the current shunt resistor. and that could blow the ass out of the current shunt resistor. so you want to clamp the voltage.

The reason they use a diode bridge like this is just to give a slightly higher voltage. I Won't go into the details, you'd have to go into the parametric curves and all that sort of stuff, but it kind of matters down on the micro amp range and things like that. So that basically got two diodes in series and then back-to-back to actually protect it. So it might be say, a 2 volt clamping protection across your current shunt resistance.

So I'll just leave that to you to figure out what's a 2 volts across our you know, a hundred ohm current shunt or a 1 ohm current shunt, how much power can be dissipated in there and hence white. You don't want to blow up your current shunt resistor, it's just some protection so it's just protecting your resistor just long enough for the fuse to blow. Now after you fuse, it's going to go into this weird looking thing here. I've actually tried to draw a range switch and the range switches.

That switch on the front of the multimeter. and if you're taking a multimeter upike seen one of my tear downs or go do it yourself. Right now, you'll see that these little contacts wiper contacts on these range switches and there's traces on the PCB. So I've just sort of, you know, simulated that.

I've got two different positions here basically. and the red just shows the short in bar, therefore the microamp range or therefore, the milliamp range. So it's just a switch, basically single-pole double-throw so on the microwave range, it goes straight into a 100 ohm current shut resistor. Easy.

That's a very, very typical value you'll find on probably most multimeters. Very close to that sort of value for your micro amp range. And then if you switch to the milliamp range, well, it disconnects this hundred ohm resistor and then goes it down here. And we've now got a 1 ohm current shunt resistor and that's actually in series with the art 10 milli ohm current shunt resistor down here.

and sometimes they might actually put in not one Ohm, but they'll actually put in nought point nine, 9 ohms like that, or zero r99 if we want to keep that terminology so that when you put it in series with the ten milli ohms down here, it equals 1 ohm total. So it's actually using both of those as the current shunt resistor effectively. And the reason they do that engineers just like nice round numbers. It comes out nice.

You can. It didn't matter if you did that and had 1 ohm plus 10 milli ohms down here, you calibrate it out in software, it's no problem Now, Unlike for the 10 milli ohm shut resistor down here. This one up here I've only shown one wire gone off because you don't really have to four-terminal measure that you don't really have to do it because the PCB trace resistance is a tiny, tiny fraction of that hundred ohms out up here. It's going to matter for this one own one because you're getting down there.

So typically they might take a sense point there on that 1 ohm resistor and actually the other sense point down here. so they're actually using both of those as the current sense resistor. But they are typical values that you'll find in probably the vast majority of multimeters out there hundred ohms, 1 ohm, and 10 milli ohms. So now let's take a look at this table down here and see what our burden voltage is for the different ranges.

A typical multimeter I'm taking the case of a 50,000 count multimeter or a 5000 count multimeter so it will have a 500 my cramp range: 5,000 microbes or five milliamps. It's actually microbes as we'll see, but it could be displayed as five milliamps, then 50 million. It's five hundred, five amps and then ten amps down. Here, ten amps is limited by the power in the current shunt resistor and other stuff.

Sometimes they can go up to 20 amps peak for 20 seconds or something like that. Then you've got to let them cool down, otherwise the current shunt heats up too much anyway. So these are the different shuts that are used. So in the micro amp range both 500 micro amps and 5,000 my cramps, it's they switch in the hundred ohm shunt resistor here and in the 50 milli amp and 500 milliamp ranges.

Then they switch in. You can put it down to the milli amp setting, you switch your range switch to the milli amps goes down here, and then you're using your 1 ohm current shunt resistor. And then when you specify amps, you've got to physically move not only well, put your switch to the amps millionths position and then move your probe down to here. And of course, it's using the 10 milli ohm resistor down here for the 5 amp and 10 M ranges.

And then if you just use Ohm's law 500 micro amps times 100 ohms here, then that's 50 millivolts or what's called 50 millivolts full scale. Or sometimes you read the datasheet for a multimeter. it might say the burden voltage is 50 millivolts max. or something like that, they might use a max figure.

it's the same as I'm just using full-scale there, so that is a typical figure. and then once you go up, of course we're using the same current shunt resistor here for both of these ranges. So, but because this one goes up to 5,000 microamps, you've got to multiply 5000 by crabs the maximum figure maximum current you can measure on that range by 100 ohms. Bingo.

You get 500 millivolts full scale. So as you can see, we've got the same current shunt resistor being shared between two different ranges and we get two different burden voltages here. 50 millivolts. That's not really a big deal, you know, Like, you wouldn't really worry about that.

You'd be pretty darn happy if your multimeter had 50 millivolts burn voltage on every range. That'd be a kick-ass multimeter. Let me tell you. But 500 millivolts? That's half a volt.

So if you're measuring a 3.3 volt rail, the current on the 3.3 volt rail, it's dropping it down to 2.8 by the time it actually gets to your chip in your circuitry. That can cause a lot of problems, so that's a real issue that's really quite high. And then you can just go do the same math here. 50 milliamps times 100 is 50 millivolts and it's the same order like this.

So 500 milliamps times 100 500 millivolts Again, So we've got these didn't sets of ranges like this based on our current shunt resistor and the amps. One down here: 50 millivolts and 100 millivolts. So you can see that there's a couple of ranges in there that are really troublesome. the 5000 My Crab and the 500 Milliamp.

We really want to fix those, and just to be complete, Byrne Voltage is often, in fact, probably more correctly, specified in volts per ants. So I've just stated the volts per ants. figure and I you can go through and double-check that anyway. we'll work with the full-scale Byrne voltage here.

But what that burden voltage here does tell you is it allows you to calculate. If you're if you're on the 500 micro amp range and you're only measuring a hundred micro amps, then you where point one milli volts per micro amp. so the hundred micro amps will give us a 10 milli volt drop on there. And of course that's obvious because it's 50 millivolts full scale where one-fifth of that 10 millivolts.

but that's the thing Murphy will get you every time. I Guarantee that your project you're trying to measure will want to take like 490 milliamps or something like that. so you'll have to go. If you want the most resolution on your multimeter, which you do, you'd go to the 500 milliamp range, but then you're going to get a 490 millivolt Burdon voltage drop.

It's terrible. now. There's actually a couple of ways to overcome burdened voltage. With just your regular multimeter, you can I switch up a range.

So if you're measuring that 490 milliamps, you can switch up to the 5 amp range and you're going to be dropping bugger-all. What are you going to be dropping? They're like, you know, 5 millivolts, right? Bugger. All but you. You lose resolution on your multimeter so it's a trade-off The other way to do it is to hook your project up to a power supply.

A tweak that power supply to compensate for the drop on your multimeter, the burden voltage. But then if your product is changing currents all the time, it's not necessarily a good thing to do. But as many of you may have already guessed, these figures aren't right. It's a bunch of theoretical.

BS Why? Because we've only taken into account the actual shunt resistor value in here. We haven't taken into account all the other stuff which is in here, and well, what other stuff you might be saying? Well, we've got some contact resistance here on the switch, but that's not going to be much, right? It's gonna be millions. it's gonna be. You know, nothing, right? Really Compared to one Ohm and a hundred Ohms to? don't even worry about it.

But we've got a fuse and we're gonna fuse here as well. But you might be thinking, well, fuses are just a bit of wire, right? that melts. It's a short-circuit Ah, these Hrc fuses, and in particular, the high-voltage ones. the thousand volt ones you want to use for our safety and that are specified into your high-quality multimeters.

I actually have quite a high resistance in them. and we'll take a look at the data sheet and we'll measure a couple of these typical fuses and you'll see that the fuse resistance can actually be higher then your current shunt resistor In here. you might be using a 1 ohm current shunt resistor for your milliamp ranges here, but your fuse might be 1 ohms or even two or more ohms so it's higher. It dominates your voltage.

so there are 500 millivolts our burden. Voltage that we thought was fairly bad down here it can be easily be double that. In fact, you can almost on a good quality multimeter with that value shunt resistor you can guarantee and it's going to be double that. Pretty much so it just measures some real fuses.

here. they're cold DC resistance at room temperature and let's actually see what they are first. we'll actually know this out. I Like using my LCR meter for this because it goes down to a hundred micro ohms resolution.

Very nice. So this is this, um, you know, top, you know, really good quality ASTM Hv6 2600 milliamps thousand volt One: Okay, so this is a thousand volt whew should typically find in a multimeter. There we go. You do get around about that one own figure.

let's try another one. Seba Another top brand at 400 milli amp one, this one's a bit lower. Once again, it's a thousand volt rated on there. and what does this one measure? Look at that one point Three: Yeah, that might be because it's a bit lowering current, but it's it's that order of things.

And hey, let's take a look at this. big Siebel one blew this big-ass thing. 440 milliamps You might think ah, this is going to be really low, right? This is a multimeter fuse. One won't worry about one.

Ohm. Once again, unbelievable. And this our bus fuse bossman fuse. The ones that I think are flukes specify these ones so it's 440 milliamps again.

and that one's better. Point Six Six Volts is that? I Don't know if that's a thousand volt. Is that a thousand volts? Yes, it is a thousand volt rated so that one's not too shabby. Ah, and look, here's another robust fuse.

This is a 1 amp one. Okay, so you'd think this would be really low because it's one amp, no siree. Bob That's still Point Five Five Ohms. That's very significant.

And here's an 11 amp one. So this is typically on the 10 M range. So once again, Quality one Seba A thousand Volts. Excellent.

And there you go. That's around that 10 milli ohm figure that we were talking about. And once again, here's a fluke. Ladies, a little fuse design for FL use either.

designed for use in the flukes. Once again, that one's going to be around that 10 milli ohm figure as well. I'm not sure if you can see that, but this is actually a 500 milliamp fuse. I've got two different 500 milliamp, just Em 205, you know, crappy one hung low bred glass fuse.

In fact, this one's not. I'll show you. This one is though. this is just an absolute GP right? So this is 500 milliamps? Okay, and let's have a look at what this one is.

Look at that. Look at that. Less than a hundred millions? 93 Millions for half an amp. So these crap little glass fuses which you should never use in multimeters if you're doing anything serious at all.

and you know these top-quality thousand volt Raider ones are like ten times larger resistance. That's just the you know, we're into material science now, so if anyone knows I don't really know what causes that. It's the material inside and construction. Yeah.

I Don't know if anyone's actually got any real proper detailed info from the manufacturers on what's causing them to be this high, but the fact is, they are. And then we've got this one here. which is like got a little last ceramic former in there. It's a fast blow 500 million fuse, yet again, only 250 volt rated okay.

and that one. This is not a no-name er, it's got all the requisite standards and stuff like that, but it's you know. point three Ohms. So still one third of the resistance of a proper one at a similar sort of rating and you're going to see a similar thing on the amps range here.

With the 11th HRC fuse, it's about 10 million or there abouts about the same as the shut, but typically on your aunt's ranges you're measuring bigger system things and using probably at a higher input voltage like 12 volts or something like that going into your product. You're not generally measuring low logic rail and low voltage rail stuff, so it burden voltages typically never really an issue on the amps range. It's not really a problem that needs solving, but certainly on the Milliamps and the Micra out ranges Here these two ones in particular, they we really need to fix those so let's take a look but may not be as easy as you think otherwise every manufacturer fix it, but they don't So how do we fix this burden voltage problem? Oh, it might seem easy just like my microcurrent. I use very low value shunt resistors and I use a Times 100 amplifier times 100 amplifiers.

A little bit tricky offset noise and stuff that starts to be a problem, but hey, we could say drop this hundred ohm one especially for this range here 5,000 microns. we can drop that by an order of magnitude ie. 10 times down to 10 ohms and then we can feed that into a Times 10 amplifier which shouldn't be too much of a bother. and Bob's your uncle.

We've fixed the burden voltage on the 5000 micro amp or 5 milli amp range here and likewise we could change this 1 Ohm 1 for the milliamps. We can change that down to 0 R 1 or point 1 Ohms and then once again take that out and we put that into a Times 10 amp and Bingo! and like I said, we don't really have to worry about the amps range so we're not going to bother fixing that. But surely that's all we have to do. and we've fixed our Burton voltage problem.

But ah ah, you remember the fuse? We might have dropped this by an order of magnitude, right? and nice Knot point 1 Ohms I Yeah, that'll drop our 500 millivolts full scale down to 50 millivolts. Yeah, for the shunt resistor, but you still got one. Oh, and your fuse up here. so it's still going to be in this order of 500 millivolts.

Sure, you've made an improvement. You've like hubbed it. It used to be a volt because of the 1 ohm plus the 1 ohm in the fuse. So that was you know you've halved it, but that's you know it's almost not worthy of you.

You know the cost of implementing you. Nice, fairly reasonable cost times 10 low offset chopper amplifier in there like a max 42-38 like a using the microcurrent. It's almost not worthy of the cost for that. So really, we can't just do that.

We have to do something with the configuration here to fix this because this fuse a real pain in the arse and we can't just get rid of it because the fuse is all part of the safety radians. You know, the UL testing and their cat standards and all that sort of jazz. you know? can't just take it out willy-nilly just do and get that. Although you can temporarily take it out and do that, and you can lower your burdened voltage your multimeter.

But that's not what we're talking about here, trying to fix it from a design standpoint. Now, some people might mention poly switches. You just wait. probably switch in there and she'll be right.

Well, it's not the same thing. you don't have the same high rupture our protection, the Ark over and everything else. There's a reason that these high rupture capacity fuses are used in multimeters and we want to stick with it. Now there's several ways you're going to approach skimming this cat.

and well, one of the first things that might come to mind is, well, and you might have actually seen on some multimeters. Instead of having milliamps here, let's have a combined milliamps and amps jack here and then take this out to our amplifier which can be times 10 and times 100 for example. So now we can actually go through with this would be 0 R 0 1 and 0 R 0 1. Let's go through and actually do the calculations again to see if we can actually do this with the X 10 and X 100 amplifier.

So the burden voltage is now. Well, this remains the same 5 amp ranges was 50 millivolts before it's it's still 50 millivolts because nothing's changed. But now we've got the milliamps with our 10 milli ohm current shunt resistor here. So it was 500 millivolts full-scale Before now it's 5 millivolts full-scale and for the 50 milli amp range here, well it was so 50 milliamps times point zero.

1 Ohms is 500 micro volts full-scale and well, that might sound ok. 500 micro volts full-scale drop across here just whack at times, 100 amplifier in and Bob's your uncle right? Well no, let's take a look at the data sheet for the max 42-38 slash 42:39 that are using micro current. It's one of the best low offset almost zero offset chopper amplifiers on the market. and it's got a typical in quote marks offset voltage of nought point 1 micro volts and you of course model have to multiply that by the gain here.

and if you have a look at the micro current here you can see it is very typically around about that naught point 1 volt epical figure on the datasheet here at room temperature and I've got it. Actually the input shorted there like that but you know we could have. we could have it on the actual range itself. There you go, it's on the 10 milli ohm current shunt resistor there.

You'll notice that it is not point O one milli volts or can get that high interests a bit with temperature and that stuff like that but the typical figure yeah it's 10. Let's take it as say 10 micro volts on here, but because this has got a Times 100 amplifier on it, you're going to divide that by a hundred and that's the input offset voltage. and it is a roundabout. that typical figure you find in the datasheet.

but hey, the maximum figure. If you're really going to town, the maximum figure could be up to 2 micro volts, but hey, that's over the entire full temperature range and worst-case process characteristic and everything else. But I've manufactured thousands of these and each one's individually tested and it really is that low. and that sounds pretty low.

But hey, let's take a look at the resolution. If we've got a 5000 count multimeter, we might get away with this. but you know we designed a reasonable multimeter here. It's let's say it's 50 thousand count, four and a half digit class multimeter.

What's the resolution? What's that least significant digit on the display representing in terms of a voltage at this? Patek the point across the current shunt here. Well, at 50 millivolts our full-scale 50, you can see that it's that's if that's 50 millivolts, it's zero Zero zero after that. So it's 1 microvolt. And likewise, we just scale it down by a decade.

5 millivolts, full-scale point 1 micro volts. Bingo. We've already matched the typical offset figure of our Op Amp, so we're starting to get a bit scared now. But now we want the 50 milli amp range 500 micro volts full-scale with.

so if that's 500 foot the decimal point there, Zero zero. We're talking about point Zero. One micro volts resolution. It's ridiculous.

It's an order of magnitude better resolution than what our amplifier is actually capable of. So when you work in your times 100 amplifier in there at that typical point 1 microvolt offset is going to be amplified a hundred times. So you're on your 50 milli amp range, you gonna get the couple of least significant digits just flapping around in the breeze because, well, that's just the offset voltage. Sure, you can fix it with like the null button on the multimeter, but it's going to drift a bit.

It's going to change with temperature and all sorts of stuff. And really, people don't expect a multimeter specially on the milliamp range to be flapping around with two least significant digits in the breeze. So really, that is not a solution. We can't just work in the times 100 amplify there because the best shop rep you can get is not going to be able to do the business.

But hey, we are getting towards a solution. So that one's actually a tick. That one. It's probably a tick.

The maybe the least significant digit might flap around by a few digits, but you know it's probably going to be good enough. but this one is definitely out. But hey, there's probably no reason why we couldn't have the Amps terminal actually do our 10 amp hour, five amp, and our 500 milliamp ranges. Because we really are quite stuck with this 500 milliamp range.

We can't use a 1 ohm current shunt resistor or a point 1. for example, because our we've got to go through this six hundred milli amp fuse which is going to be 1 ohm. So we're going to be stuck with that high 500 milli volts burden Volta says almost no way around it apart from implementing some sort of switching solution here that goes through our 11 amp fuse. but then we'd have to put some real beefy, heavy-duty MOSFETs in there, or a relay to our switch our 10 milli ohm current shunt resistor and there is one like a high-end gossin.

They actually do that. they do actually MOSFETs which the 10 milli ohm current shunt resistor in there and then they can switch in once you've got rid of that, then you can put other resistors in parallel here. So that's why they actually only have one amps jack like this and it can measure down to like a 100 micro amp range or I think it's 300 micro amp range or something like that because then once you disable, if you're able to disable that current shunt resistor there, then you can put others in series real easy because you know if it's point 1 Ohm or something like that, you can switch it in no problems. So that is one possible solution just to do away completely with all this crap up here and just do it all from the one Jack we're switching, but that's not what I want to do here I want to solve the problem for the existing Jack's that we've got available.

One of the reasons is is that those MOSFETs or a relay or whatever they're really big ones have to be big and beefy. They take up a lot of room inside a multimeter so you've got to clear out all the space. So I'm going to propose stick in with using the Amps jack and the 11-hour fuse in the ten milli Ohm shut for the 500 milliamp range. but this 50 milli amp range.

Hey, let's go back to the existing solution here and just use. We don't even need this 10 at this point. 1 Ohm shunt. here.

We can get away with just our 1 Ohm shunt in there. Because we only had originally, we only had 50 millivolts full-scale drop that's more than adequate. Even with the 1 Ohm up here, it's only going to be like a hundred millivolts. typical full-scale So I'm reasonably happy with that.

That's lowish burner voltage. It's not mutton. It's not microcurrent low, but hey, you know it's good enough. So I've got and filled in a more detailed table here with the typical drop we're going to get for each of these ranges which I'm proposing here plus the value due to the fuse up here.

So at the fifty mili amp range, let's use our exist in 1 Ohm resistor here so we don't really have to change anything. and then that gives us 50 millivolts our full scale. So that gives us 50 millivolts Plus Remember another one I'm up here so that gives us another 50 millivolts 100 millivolts air. We're pretty happy with that.

I'm not going to quibble over 100 millivolts true system burdened voltage. That's pretty good. It was really the 500 millivolts and the 1 volts up you wanted to fix, so that's an order of magnitude lower than that beauty. So that gives us 1 microvolt resolution.

We don't need an amplifier in there that can just go up bugger off into the existing multimeter chips which has its own internal amps and stuff like that, but it expects that 50 millivolts so it's not a problem so we don't need any extra amplifier for that range. Now for the 5000 micro amp range, instead of having it go before we had it going into the hundred Ohm or 10 Ohm resistor over here. Let's actually put that into the 1 Ohm resistor. so we just have to reconfigure our range switch there so it will not.

really. We just call it milliamps instead of 5000 microwaves. Just call it 5 milliamps. So it goes through here into our 1 Ohm resistor if we do that instead of the 500 millivolts we're getting before.

Bingo! we're now getting because it's 1 Ohm 500 5 milliamps times 1 Ohm is 5 millivolts. Is it not? Plus the extra Ohm up here 10 millivolts. Total beauty, right? And once again, our resolution is only point. 1 micro volts.

it's in. You know it's It's doable with the that maximum chip that we can actually get and we only need that times 10 amplifier. And then this micro amp range is now only used for one range and that is now. Of course we reduce it by an order of magnitude.

10 Ohms. Just like we said before. So 500 micro amps times 10 Ohms is 5 millivolts plus 1 Ohm up here. 1 Ohms and 10 ohms.

It's if something is an order of magnitude less. You just go math. So I've just written there in there doesn't you know it's going to be like plus me and 0.5 millivolts or something doesn't matter me. So 5 millivolts System: A burden.

Voltage Absolute Ripper And we just need our times 10 amp there. I Think we've got a solution? So what extra circuitry do we have to add to this thing to make it work? well? We need a couple of muxes in here, ie. just some switches to switch the voltage across here. So we've got three points now.

We've got one across our 10 A.m. shunt resistor, one across our 1 Ohm shunt resistor, and one across our 10 milli ohm shunt resistor. So we can select either of those three inputs. It comes out here and this is sorry.

that's a Times 10 amplifier that goes into our Times 10 fire which amplifies that. and then we've got another MUX which can select between the X one or the X 10 position because we need both of those selections here for that and that just goes to the output. And of course, yeah, this is you. Remember we said down here that our sense in matters so you know we'd bring our sense line there and you have to I go into details of how you would lay that out on the board, but yet we would have to take that as our sense terminal because that matters.

Otherwise, we'd get offset issues are caused by the traces and things like that. but that I think is L better multimeter. It's not super low, you know. Burden Voltage: Absolutely fantastic.

but hey, it's probably a good order of magnitude or there abouts better than your typical multimeter cuz some can be like like a worst case. we're talking 100 millivolts here. it's not. So it's very typical down here.

We haven't fixed anything with the Amps range, so that's just you know, a typical multimeter on S. But as we said way back at the start, it's not really. For most measurement applications, it's not really a problem. I Don't think I've ever encountered an issue where Burden Voltages been a problem on the Amps range, really.

but there might be some obscure case. but we don't really need to fix that. but we definitely fixed these five five milliamp range in the 500 milliamp range we had problems with before. Ripper So they have it.

This has probably been a lot longer than what I intended, but I think this is quite a neat solution. There's other ways to do it as I said switch In having the one input jack and having MOSFET switching and stuff like that as you know, a really nice way to do it. but it's big and complicated and expensive. So yeah, it's you know, but just to modify an existing type traditional meter design like this.

Um, that probably does the business. Yannick Kind of confusing part, as maybe the 500 milliamp range here would have to be marked on that jacket to be amps and 500 milliamps. and this would be milliamps and micro amps like that. but you just annotate it on your silk screen on the front of your meter and Bob's your uncle.

So there you go. Hope you got something useful out of that. If you got any better ideas then yeah, leave it in the comments down below. Hope you enjoyed it.

Catch you next time you.