Hi Welcome to the Eev blog an Electronics Engineering Video Blog of interest to anyone involved in electronics Design I'm your host Dave Jones Hi It's a bit of a random one today and it comes from the Eev blog. Forum I Saw a post a couple of hours ago from a viewer by the name of House 91320 and he posted some photos of an Open Source Hardware project he's working on cool I Love Open Source Hardware projects. But what piqu my interest was that it was an open Source Hardware multimeter. And you know I Love multimeters I Love talking about multimeters I Love talking about multimeter design.

so I couldn't help but be interested and come up with a few ideas of my own. So I thought we'd take a look at it I've done some quick Doodles in Dave CAD here. let's check it out. Now here's some photos of House's Open Source Hardware multimeter mockup.

It's just a, you know, a first pass mockup and it's not bad at all. But I saw it and I went well. You know it's just a multimeter. It's a regular looking multimeter.

It's got a graphic display though, it's got a range switch and it's got volts, ohms, and amps. Jackson Well, that's pretty much it. It's got USB interface to a PC Okay, but yeah, it's just a multimeter and I got to thinking, well, you know there's just so many multimeters on the market that just have all those features. So why really do an Open Source Hardware one? So I thought well, it's got to have something novel.

It's got to have something interesting that other nothing else on the market has. It's got to have that compelling feature or combination of compelling features to make it worthwhile. So spent 5 minutes did some Doodles came up with some ideas. So I Started off thinking about multimeters and well, quick thought.

what do they all have in common? Well, it's pretty obvious they all are basically a single measurement type device. They've got a common Jack They've got a Volts, Ohms Amps Uh, well, Volts and Ohms Jack and they've got an Amps Jack And well, really, there's very few on the market that actually do more than that. And I Figured, if you're going to actually design your own multimeter, why not make it do more than the standard multimeter. Add some novel capability to it.

And one of my favorite multimeters is the Metrahit energy and it measures volts and amps. It's still only got the three input Jacks here, but it measures volts and amps at the same time. and it's got a triple display and it displays power uh, among other things. And it's got data loging and stuff like that.

And there are another novel multimeter on the market is the Fluke Uh 233, which has the removable display on it. So it got me starting to think, well, maybe if you could do more than just measure power like this and more than just having a removable display or something like that. Sure, there's a lot, you know there's multimeters out there. They've got graphic screens, data login, USB interface, all sorts of stuff, but they all pretty much come down to.

They're basically a single input function. They can't log or measure more than one thing at a time, so that's where I started from. As you may know, I've mentioned on here before that any good lab should have more than one multimeter. In fact, I've shown a case or two where you really need four multimeters for measuring the input power of a product and the output power at the same time.

So that got me thinking, well, what if you could replace that with one multimer? That' be awesome. So let's take a quick look at my Dave CAD drawing. see what I've come up with? So I present to you Dave's kind of Novel multimeter concept. This is what I uh came up with very quickly I don't know I haven't slept on it, but I just thought I'd come up with something different.

What have we got here? Well, you'll notice. One of the main things is we've got multiple input Jacks here. In fact, we've got four separate channels all with their own separate grounds. So it's basically a totally isolated by the way.

So it's a four Channel isolated multimeter. Now, when I first came up with the idea I thought oh wouldn't it be great to have ground vaults and amps like and and then like have three or four channels of those and then I thought, well, you know it's a bit Overkill So I sort of limited myself a little bit just to uh two voltage channels and two amps channels. Now the Uh one of the voltage one of the input channels. Okay, it has all your standard functions.

Most of the time you might use this as a single Channel multim media. Plug your leads in here and you can do your volts. HS Caps diode? What? continuity? Whatever you want. Okay, that works like a regular multimeter, but at the same time you have the capability to to have a second Uh voltage channel here at the same time and a second and a first and a second Amps channel so you can combine just like on the gosen.

uh, energy multimedia. You can combine volts and amps. That's why I've labeled them channel One here. You don't have to worry too much about the semantics of how all this works.

You know it varies. it's just a concept, but uh, you can take, say the if if you're talking power, you can take Channel One Volts time amps and it can display power. Likewise, on the second, Channel Volts and Amps displays power and I've got a secondary function here which is an output which I originally was going to have this as another separate output, but I decided that uh, no, it was a bit too many connectors already. So I thought well I'll just, uh, integrate it into the existing ampjack.

Now the beauty of this is that it's not common ground. it is to they are all totally electrically isolated channels and I don't think there's probably any general purpose multimeter on the market that actually has that. and I've shown this in one of my videos where um, because the Uh Gosen metrahit energy actually shares a Ground Terminal I really wasn't able to uh, take really precise measurements of some battery uh of, you know, battery consumption and things like that. I'll have to link the video in there to show you what the actual issue was, but you get around that by having two totally isolated channels like this and what have we got on the rest of it? Well let's take a look at the Uh overall concept.

I've got these nice little, uh, wanky, uh hand sort of grips in here I kind of like that sort of concept. Please excuse the crudity of the model I didn't have time to build it to scale or to paint it. to quote Back to the Future but uh, my Cad drawings kind of suck. but hopefully you can get the con now.

I'm a big fan of big seven segment displays I think any multimeter has got to have big seven segment displays now? Um, House's design just had the one big Um graphic display and it was color and it was backlit. TF Cheo Power like there's no tomorrow? No, no, please give me on my multimeter. I Want seven big seven segment displays Now the Gosen Metr hit Energy for example, has three displays so that you can display voltage and current and power at the same time. But I thought well yeah, that would be nice if I could had triple or even quadruple display I thought about so you can display the actual parameter from each.

uh Channel but it gets messy when you start talking about the design of this. Um LCD if you got three or four displays on there all with uh, you know, 50,000 counter all five-digit displays like this. It really gets quite complicated when you can get down to the design details of it. So I decided to have two big uh, 5-digit displays and a separate.

Just as a bonus is separate. uh, say for example, 256x 64 uh, monog graphic LCD display and that can be used for say, soft buttons. You could have four or five soft buttons under there. You could have a menu base system, you know I hate menus on mully meters, but when it has this much functionality, you really can't.

uh, get away with it frankly. So you've got to have some sort of menu capability. and the graphic display can display not only menus, but it display data, login and simple, uh, graphs and things like that, uh login stuff. and of course, um, it's got an SD card down here.

Now what multimeter on the Market's got an SD card? Now the reason I chose the SD card over a USB interface. In in in my mind, the SD card actually, um, negates the need for a USB input uh, terminal because you can, um, uh, USB input requires isolation. It's a real pain in the butt. and well.

I Just like the idea of being able to log Standalone to an SD card and you can upgrade firmware by there. And you can do all sorts of stuff. When you integrate an SD card into a login multimeter like this, you can log uh, voltage current across all four channels, power all sorts of things, and log it to the internal memory and then dump it to the SD card. If you want to save power and stuff like that, there's all sorts of, uh, smaller details like that when you actually get down to it, but I reckon you can do away with USB Save yourself a lot of design effort and hassle by trying to isolate the USB input and use an SD card.

Now you'll notice: I haven't put a range switch on here I Haven't really decided the concept for that. Whether or not you actually need a a traditional rotary switch on a design like this, maybe not I'm not hard set on that so it could be like a um M You know they could be like I don't know. 10 buttons Big, large, uh, easy to press soft buttons. things like that.

So maybe you can go for a full button interface I Don't know. Haven't sorted out the user interface details to be determined. Absolutely. And let's take a look at some of my notes up here.

As we've mentioned, we've got four isolated channels two vol, two current just for the sake of Simplicity I Don't think you need uh, uh, probably any more than that. It's just nice to have two voltage channels and two current channels I Think maybe you could argue that uh, the current one should be uh, dual-purpose voltage inputs as well. so you could have a 4 channel voltage Data Logger uh I haven't gotten that far into it. anyway.

Now the um, the output Jack down here. this one I talked about it could actually be separate. It could actually go on the side here. It could even go on the top of the multimeter up here.

Now what I want to use that for is I've talked about this before as I want a programmable constant current feature so you can test LEDs at a specified current or you can have like a function gen. A lot of multimeters have got a function generator uh output. You can Define the frequency? whatever. Um, it could even have um, not just a uh, digital um signal output, but actually a proper function generator with sign triangle as well possibly.

and I think what would be real Handy is a little power supply output. you could adjust from say zero to I don't know, 6 volts or something like that and you could power your project. Sure, you're going to suck your batteries uh, dry if it takes a fair amount of current, but there's so many projects these days that require small amounts of power and why not have your multimeter Supply that power once again isolated to your project? I Think that would be terrific. Now we talked about the SD card negating the need for the isolated USB there and login.

So I don't need to talk about that anymore. Now here's where I got to thinking about the Fluke 233 with the removable display. I Originally had, uh, a first rough sketch of this. It would actually have three removable displays that you could actually take out cuz I had three channels at the time.

Um, and then I thought about four. Oh, it's just I don't know. It's all very mechanically hard to actually integrate a a removable display into this. So just build.

I Mean you don't need to have a removable display on a multimeter. It's handy. you just have um, but you can just have a separate one and wireless so you integrate Bluetooth Zigby whatever for a second display or it could be for a PC or iPhone interface or something like that. and then if people want to if they need that capability, they can just buy a second display that all it does is contain the actual display which uh, links to the meter and and you know, it's got a magnet on the back, its own battery power, all that sort of thing.

Just like the Flute 233 except it's not removable, which uh, then lowers your system complexity designing this multimeter. it's just another thing to goof up quite frankly. Now, I've got uh, two five-digit displays here. We talked about that and I haven't really worked out details of how you would actually display.

One might display volts and amps, how the combinations work with power and then voltage. It'd be nice if we had the triple display like on the Gosson, but uh, I don't know. I think I'd probably limit it to two. just um, the sheer complexity of it really now.

I Talked about the graphic display before. now. a key to it is it's got to be a low power. now.

You can get these tiny displays that only take a milliamp or two so they don't take a huge amount. And really, you could even, uh, have a feature that disabled that if you weren't actually using it so you can get away. you know, forget color, forget backlighting and all. you can have back lighting, but only switch it on when you need to n this color.

TFT Rubbish. Just get a nice reflective monochrome display. Thank you very much. Super low power.

Um. and of course the meter should do um LCR type and ESR functionality was mentioned on the Forum as well. for houses design I think an ESR would um be a nice feature as well LCR I Don't know how complicated is it? Well, you know the whole thing is complicated so well you may as well add those sort of features. Um, as we've talked about power display, power factor, and all the other stuff which goes along with it like on the Gosen energy and uh, I Kind of like the idea of maybe possibly having a Voice output so that it could, uh, speak the voltage or something like that.

or maybe even just say high voltage warning Will Robinson Something like that you could possibly have instead of actually having the um, the samples actually stuck in the memory in there and the processing needs lots of grunt to do it. Just use one of those voice recorder chips. Maybe you could have a microphone in there perhaps? and you could record your own uh, you know, overload, oil continuity, oil? you know, under 10 ohms or something like that war in high voltage or nothing connected or something like that. I don't know.

Voice output might be novel, might be a wank, who knows and uh, what? I've added up here is an often lacked function on multimeters is a good temperature capability, you know. I guess all good multimeters these days will have temperature capability, but they're all single. Channel and often so often I've needed to measure multiple channels. so I reckon have two separate uh, multiple temperature inputs.

Use the Uh blade type thermocouple um, standard thermocouple inputs up the top, two or even three perhaps. Um, depending on your requirements and space at the top and things like that and then you you can log. Not only so, it effectively turns your multimeter into a six Channel thing. you can still do your two volts and your 2 amps channels.

Um, but you can measure two temperatures at the same time. Imagine the logging capabilities. That would be awesome. You just plug the thermal couple straight in.

That's better than uh, wasting your inputs here with those thermocouple adapters on the input. Why not just whack them straight on the case up the top? Not a problem. And of course I'm a huge fan of big battery on multimeters, so really Double A's are the go. Um, if you start talking bigger than that, you start talking C or D size and they're really quite.

You know they're huge beasts. So I don't know how you get away with that, but just four AA would be nice I'd Shoot, for 500 hours plus 300 hours is typically taken as a decent amount of battery life for a meter. Once again, those sort of hours would only be sort for like a standard uh, you know this, just just your standard multimeter functions. Data login is going to take more and other functions are going to take more of course.

and there's the power supply and current outputs that are built in and things like that. But anyway, there's my basic concept for a novel multimeter. I Might wake up tomorrow and decide this is complete nut of crap. But anyway, let me know what you think and let me know what you'd like to see in your own multimeters.

Come up with your own sketches, video response if you want. Thanks! See you He.