Building a better multimeter...

[mikeselectricstuff]

The post about whether Rigol should do a DMM got me thinking.
Handheld DMM functionality has hardly changed in the last decade or so, maybe more, yet many other areas of testgear (scopes, AWGs) have improved by an order of magnitude in terms of price vs. performance.
More fancy features only tend to appear in higher end models, as manufacturers want to protect their full product range to compete with similar models from competitors.

However what if a new player decided to enter the market, and design a new DMM from the ground up with a focus on maximum useful features in a  midrange handheld DMM. Let's say in the $200 region.

Here's my list of what I think would be useful and doable without making things much more expensive:

Simultaneous voltage and current measurement (non- isolated with common ground, i.e. same as traditional DMM connectors), with power (simple V*I) display. Cost : this is basically the addition of a multiplexer.  Don't mind if reading rate is a little slower in this mode.

uCurrent-like low-current performance. Just add a chopper-amp. Not too bothered if accuracy is slightly lower. Anyone who needs to measure current draw to better than 1% can pay extra for that.  Cost : maybe $2

Bluetooth connectivity for output of readings. Cheap nowadays, and ideally BLE/Smart/4.0 so it can spit out readings with minimal power draw. Possibly an option by plugging in an internal module (not the ugly external lump from Agilent). Avoids need for proprietory interface cables, inherently isolated and enough range for across-the-room operation.

Variable continuity-test threshold, option to beep on open, very fast (<20mS) with optional stretch.  Maybe 2-level beep, for two thresholds to distinguish open/resistive/short. Option to flash backlight for use in noisy environments. Negligible cost

Very low resistance mode, using uCurrent functionality - not 4-wire, and not necessarily good absolute accuracy, but deltas would be very useful for tracing shorts. Option for audio output, Maybe call  it 'short-finder' rather than resistance.

High voltage (30V) diode test for zeners,  LED strings (e.g. LCD backlights) . cost : A few cents for a crude DC-DC step-up
Maybe extend this to an AC diode test - alternates test polarity at a few Hz and indicates Vf in 2 directions simultaneously. cost : Another few cents for a charge pump inverter off the diode test supply. 

Active overcurrent protection to avoid blowing fuses. (maybe in addition to a real fuse to meet safety specs, but the active cct would trip first).
 
Display : Sharp Memory LCD. High contrast,decent graphics for a nice UI but minimal power draw as no greyscale or colour needed.
E-Ink seems initially attractive but slow update and risk of 'sticking' on a 'safe' reading if something dies could be issues. 
Failing this, a mixed-mode LCD with big segments and a matrix area for UI and secondary readings - this allows a tradeoff between contrast and power draw - you can turn the matrix off when not needed.

Logging  - obviously - this has negligible cost. Maybe to a SD card - shouldn't be hard to design a  safe card slot for when you want to remove the card to dump large logs.

Basic inductance measurement - good enough to identify E12 values.
Capacitance measurement range to cover electrolytics (Fluke I'm talking to you!) and identify excessive ESR

A neat case design to retain probes/cables when not in use. Maybe a compartment to store croc-clips.



 

[mikeselectricstuff]

..and what it should NOT have ..
Colour TFT  - NO NO NO! - too much power draw, you don't need colour on a DMM.
Touchscreen - obviously.
Li-Po battery ( except as an option).
Piss-poor Chinese firmware

[junggwok]

Hi Mike

Saw your post after my comment to the Rigol Handheld multimeter idea. You might have just given Rigol an entirely new business ideas, I wouldn't be surprised in 5 years time someone actually makes something like that. (I mean how hard can it be?)

[mikeselectricstuff]

The basic question when thinking about it is this :
When you put down your DMM and have to reach for another tool - could that tool's functionality ( to the extent you need it) be included in the DMM at minimal cost? In many cases, in my experience, the answer is yes.

Oh, and something else - ability to direct read current using an external shunt - i.e. user-configurable display scaling - no extra cost. Some very obvious indication when this is set - e.g. italic digits or a big icon.

[jucole]

The basic question when thinking about it is this :
When you put down your DMM and have to reach for another tool - could that tool's functionality ( to the extent you need it) be included in the DMM at minimal cost? In many cases, in my experience, the answer is yes.

I'm quite glad you've posted this as it's a project I'm currently working on and there are a couple of good ideas in your post;  but the main struggle for me is nailing that ideal form factor.

[Wytnucls]

I don't think that would fly. Most high-end multimeters are bought by industry for electrical work, where safety is paramount. Fluke cornered that market a long time ago, even in China. No company is going to buy something with a flimsy track record, which could increase litigation and insurance costs.
I would wager that hand-held dmms, designed for electronic work, are part of a niche market. Most labs use bench meters already equipped with the features you mention, albeight at a hefty price.

[mikeselectricstuff]

I don't care about industrial electrics - Fluke, Gossen etc. will always dominate there, and the functionality of current products is fine for them.
I'm specifically thinking about electronics, mostly bench, work, where functionality is more important than being able to put it across a 3-phase 600A busbar without dying.
I think many DMMs compromise their usefulness for elecrtonics by trying to cover too wide a range of functions.
In terms of safety, I'd say the worst case it needs to handle is a worst-case of 240VAC domestic supply, and the DC voltage on a big switchmode PSU reservoir cap.   

I would wager that hand-held dmms, designed for electronic work, are part of a niche market.

Yes, absolutely, but a big niche which IMO is not served well at the moment at the price it could be

I'm quite glad you've posted this as it's a project I'm currently working on and there are a couple of good ideas in your post;  but the main struggle for me is nailing that ideal form factor.

I don't see anything wrong with the existing handheld DMM form-factor (except could be a little smaller) . It's the functionality that has scope for improvement.

[EEVblog]

uCurrent-like low-current performance. Just add a chopper-amp. Not too bothered if accuracy is slightly lower. Anyone who needs to measure current draw to better than 1% can pay extra for that.  Cost : maybe $2

Maybe not that easy.
The protection stuff already in the front end could screw up really low level ranges.
The new uCurrent does 0.05% on the lower ranges and 0.1% on the Amps range, but that doesn't cost a few dollars. Of course you can simply software cal it out cheaply.

A neat case design to retain probes/cables when not in use. Maybe a compartment to store croc-clips.

Now you are into bench-ish meter territory (think Fluke 37), or rather bulky hand-held.

You forgot battery life. Any meter that can't do at least several hundred hours ain't worth a pinch as general use meter.

[EEVblog]

Simultaneous voltage and current measurement (non- isolated with common ground, i.e. same as traditional DMM connectors), with power (simple V*I) display.

I disagree. These already exist and are rather limiting. But better than nothing of course.

The thing I find most limiting about multimeters is that I often have to have more than one at once.
So IMO a really novel meter would have 4 isolated independent inputs. Preferably all dual use, but I'd be happy with dual voltage channels and dual current channels.
Or at least a meter with separate voltage and current channels.
In fact, separate current and voltage channel can be safer because of dedicated probing.
You'd probably have to have them all powered from the one battery though, because you wouldn't want separate batteries to run out and/or leak, but that's not hard to implement.

Brings back some memories:

[mikeselectricstuff]

uCurrent-like low-current performance. Just add a chopper-amp. Not too bothered if accuracy is slightly lower. Anyone who needs to measure current draw to better than 1% can pay extra for that.  Cost : maybe $2

Maybe not that easy.
The protection stuff already in the front end could screw up really low level ranges.
The new uCurrent does 0.05% on the lower ranges and 0.1% on the Amps range, but that doesn't cost a few dollars. Of course you can simply software cal it out cheaply.

It doesn't need to go down as far as uCurrent - something like 0.1uA resolution at a burden of maybe 10R max  would probably be fine. It's more about avoiding the burden than increasing the range of a traditional DMM. Just adding, say, x100 gain would make a big difference.
This is probably the biggest inadequacy in most DMMs for electronics use nowadays.
Most of the time I'm just checking current draw to estimate battery life, find floating pins and check sleep mode is working OK -1% accuracy is more than enough.
Something I'd also like is some integration capability to measure avarage draw of things going itno various sleep mode, but there are some interesting issues there (I looked at this very hard a long time ago).

A neat case design to retain probes/cables when not in use. Maybe a compartment to store croc-clips.

Now you are into bench-ish meter territory (think Fluke 37), or rather bulky hand-held.

yeah - probably - I was thinking more in terms of a detail you can wind the leads round neatly on the outside rather than containing them

You forgot battery life. Any meter that can't do at least several hundred hours ain't worth a pinch as general use meter.

Definitely, but most meters (with segment LCDs) are already OK in this respect - Maybe should have added "battery life no worse than, say. a Fluke 87". Choice of display is probably the biggest issue here. Possibly also a selectable tradeoff between update rate and power draw. Maybe even automatic - reading rate slows when signal static for a while. This is where the Sharp Memory LCD would be a very big win - high res graphics, but contrast and current draw is comparable to a segment display.
Power-to-volume is not too different between alkaline and li-po so It's say stick to 3-4 AA cells, as easier to swap out quickly than recharge a li-po.
However li-po as an option may be useful  (more so if you can charge it via the front terminals!) - if it did have li-po it would absolutely HAVE to be chargeable from USB so you didn't have yet another charger.  For safety use some clever meachanical detail that prevented plugging USB charger in when leads are in input sockets.
Maybe use a standard phone or camera pack so you can do a battery swap. I certainly don't like the idea of a fixed internal battery.
Probably the optimum would be a battery compartment that could take AAs or a standard lipo pack.

Something that's probably at least as important as lifetime is a battery level indicator that says more than just "low" - knowing how long you have left is much more useful than a bit more life. This is something the current market is woefully inadequate at - FFS there's a 4+digit ADC in the box and all you can tell me is "Low" - pretty pathetic.

 

[mikeselectricstuff]

Simultaneous voltage and current measurement (non- isolated with common ground, i.e. same as traditional DMM connectors), with power (simple V*I) display.

I disagree. These already exist and are rather limiting. But better than nothing of course.

Not very common, and a LOT better than nothing for minimal extra build cost.
I'm trying to focus on what could be done in a traditional DMM format at minimal extra cost.
As soon as you add more inputs it adds significantly to cost, size, protection, isolation issues etc.
A commoned V/I input is fine for a large range of applications, and if doing this doesn't add too much cost, you can afford two of them for things like DC/DC efficiency testing  .
The icing on the cake would be if they could talk to each other over bluetooth to give an efficiency reading!
 

[EEVblog]

Probably the optimum would be a battery compartment that could take AAs or a standard lipo pack.

If it already has several hundred hours battery life, then there is no need for any rechargeable solution.
BTW, the Agilent meters used to have charging via the sockets.

Something that's probably at least as important as lifetime is a battery level indicator that says more than just "low" - knowing how long you have left is much more useful than a bit more life. This is something the current market is woefully inadequate at - FFS there's a 4+digit ADC in the box and all you can tell me is "Low" - pretty pathetic.

Yes, almost some meters give you approximate life left when the meter shows "low".
But once again, if it has several hundred hours life anyway, then generally it will always have enough life left for one last job.
Accurate estimate might be handy for long term data logging though.
Also, you want full confidence in all measurements when it shows low. It should either measure accurate or not switch on at all.

[firewalker]

Could it be implemented by a small team of experienced users and not a company? Or the cost would go beyond the target? Crowd funded?

Alexander.

[mikeselectricstuff]

Probably the optimum would be a battery compartment that could take AAs or a standard lipo pack.

If it already has several hundred hours battery life, then there is no need for any rechargeable solution.
BTW, the Agilent meters used to have charging via the sockets.

Yes - probably right.
 

Something that's probably at least as important as lifetime is a battery level indicator that says more than just "low" - knowing how long you have left is much more useful than a bit more life. This is something the current market is woefully inadequate at - FFS there's a 4+digit ADC in the box and all you can tell me is "Low" - pretty pathetic.

Yes, almost some meters give you approximate life left when the meter shows "low".
But once again, if it has several hundred hours life anyway, then generally it will always have enough life left for one last job.
Accurate estimate might be handy for long term data logging though.
Also, you want full confidence in all measurements when it shows low. It should either measure accurate or not switch on at all.

The big problem with "low" is you tend to just ignore it until it's too late! A few more states would help a lot. "Make sure you have a battery in stock", "Change battery when convenient", "Change battery NOW, but I'm disabling the backlight and slowing down to squeeze a bit more out" and "Game Over".

[jucole]

It's the functionality that has scope for improvement.

I totally agree!    Some of the ideas I was toying around with was inductive base-pad re-charging like a toothbrush; maybe I hang it onto the wall when I've finished for the day and it's all charged for the next day.  2 input jacks per channel for measurements (so I don't have to keep switching jack sockets).   Adding speech - so I don't short stuff whilst looking trying to look at the display;  and one of the really crazy ideas was the ability to upload repair/diagnostic scripts to it via the Bluetooth.

I did manage to blag some very new interesting DMM chipsets from one of the big players using a  A-Team Templeton "Faceman" Peck routine but I'll probably be using off-the-shelf uC / FPGA stuff for this concept project.

[amyk]

Maybe use a standard phone or camera pack so you can do a battery swap. I certainly don't like the idea of a fixed internal battery.
Probably the optimum would be a battery compartment that could take AAs or a standard lipo pack.

This would be an example of the type of feature that a Chinese company is far more likely to come out with --- instead of the "let's force you to use our very expensive proprietary battery pack" it's more along the lines of "use what's already available" that their thinking tends along. Although for various reasons, I don't think Rigol is this type of company; this sort of versatility is founded in the  shanzhai culture.

[mikeselectricstuff]

Could it be implemented by a small team of experienced users and not a company? Or the cost would go beyond the target? Crowd funded?

Alexander.

Maybe. A (very) few people to spec and do design, then crowdfund for volume part pricing and case mould tooling. The case quality would have to be comparable to current mid-range models.
Most of the individual enhancements are not really that hard.

Oh, and of course it should start up absolutely instantly (No embedded OS or flabby firmware please!) Open source firmware would be nice. Not so bothered about hardware as long as schematics are available.

[Marco]

Simultaneous voltage and current measurement (non- isolated with common ground, i.e. same as traditional DMM connectors), with power (simple V*I) display. Cost : this is basically the addition of a multiplexer.  Don't mind if reading rate is a little slower in this mode.

This is just going to go wrong far too often, I'd want separate grounds, use a high side current sensing IC to measure the current or two isolated analogue sections.

uCurrent-like low-current performance. Just add a chopper-amp. Not too bothered if accuracy is slightly lower. Anyone who needs to measure current draw to better than 1% can pay extra for that.  Cost : maybe $2

Just make sure you need to take extra steps to activate the mode, since input protection is going to be minimal in this mode ... I'd hate to just put it in by accident and fry everything.

Very low resistance mode, using uCurrent functionality - not 4-wire, and not necessarily good absolute accuracy, but deltas would be very useful for tracing shorts. Option for audio output, Maybe call  it 'short-finder' rather than resistance.

Why not 4 wire?

How do you want to do the active current cut out? AFAICS only relays will have low enough resistance over rated input voltage, high voltage MOSFETs will add too much burden. Can the relay be turned off fast enough?

[mikeselectricstuff]

It's the functionality that has scope for improvement.

I totally agree!    Some of the ideas I was toying around with was inductive base-pad re-charging like a toothbrush; maybe I hang it onto the wall when I've finished for the day and it's all charged for the next day.  2 input jacks per channel for measurements (so I don't have to keep switching jack sockets). 

Single socket adds complication ( and precludes dual V/I measurement). I think most people accept having to swap for I measurement. Also has some safety advantages. Maybe a change I'd make would be a single 10A socket and amplifier for mA/uA instead of a second current socket.

 Adding speech - so I don't short stuff whilst looking trying to look at the display;  and one of the really crazy ideas was the ability to upload repair/diagnostic scripts to it via the Bluetooth.

Speech could be less silly than it sounds, and also minimal cost to implement. You'd be looking at low-en ARM to support a graphic display, so it ought to be able to do speech all in software - not a problem if the display freezes when speaking. if it has Bluetooth you could do BT audio to an earpiece. You'd definitely want some flexibility in adjusting speed and content though. (Make your DMM talk like Dave!  )

but I'll probably be using off-the-shelf uC / FPGA stuff for this concept project.

can't think why you'd need FPGA or even CPLD for this.

[mikeselectricstuff]

Simultaneous voltage and current measurement (non- isolated with common ground, i.e. same as traditional DMM connectors), with power (simple V*I) display. Cost : this is basically the addition of a multiplexer.  Don't mind if reading rate is a little slower in this mode.

This is just going to go wrong far too often, I'd want separate grounds, use a high side current sensing IC to measure the current.

Totally disagree. Most of the time you want to know V and I of the same source. Seperating adds significant cost.

uCurrent-like low-current performance. Just add a chopper-amp. Not too bothered if accuracy is slightly lower. Anyone who needs to measure current draw to better than 1% can pay extra for that.  Cost : maybe $2

Just make sure you need to take extra steps to activate the mode, since input protection is going to be minimal in this mode.

No. It would use teh existing shunt, just with some gain. Protection no different

Very low resistance mode, using uCurrent functionality - not 4-wire, and not necessarily good absolute accuracy, but deltas would be very useful for tracing shorts. Option for audio output, Maybe call  it 'short-finder' rather than resistance.

Why not 4 wire?

Extra cost. I'm specifically thinking about functionality for finding shorts on PCB - delta and audio will add a lot of function at minimal cost,. especially as you could re-use the current amplifier.

Remember I'm focussing on how a normal mid-range DMM can be made more useful, not trying to design a high-end bells-and-whistles thing.
 

[EEVblog]

The big problem with "low" is you tend to just ignore it until it's too late! A few more states would help a lot. "Make sure you have a battery in stock", "Change battery when convenient", "Change battery NOW, but I'm disabling the backlight and slowing down to squeeze a bit more out" and "Game Over".

Agreed.
Big scrolling text as last resort - "Change the F'ING battery you moron!"

[EEVblog]

Could it be implemented by a small team of experienced users and not a company?

Yes. Although if you were really serious and wanted to go into a production and be a serious player, you'd try and team up with an existing meter OEM in some way I suspect.
These things work better as a dictatorship though. There have been a few big threads on DIY community meters, and it always ends up compromise and never happens because of having too many cooks.

Or the cost would go beyond the target? Crowd funded?

If you wanted to produce a real production market ready product with custom injection molded case and range switches, battery compartment and all the bells and whistles then it could easily go over budget and fail. More likely than not I'd say.
I wouldn't want to do it that way, I'd prefer a more off-the-shelf type DIY looking approach.

[jucole]

but I'll probably be using off-the-shelf uC / FPGA stuff for this concept project.

can't think why you'd need FPGA or even CPLD for this.

It's got quite a few more features that will need an FPGA which I only really added because I wanted to learn FPGAs.

[firewalker]

No. Not a community thing. I would die instantly. And no open source/hardware as requirement. I was thinkig a group of 5 as a max.

I would also like a settable voltage level pass/fail beep.

Alexander.

[peter.mitchell]

one big feature - alert the user on the display that the fuse is blown when the fuse is blown instead of reading 0.000, a lot of meters do this but there are significantly more that don't.
important normal features like jack sensing - continuous beep when plug is in amps jack on volts measurement ect, same as above, lots do, lots also don't.
in the continuity measurement/beeper, have a 2 stage beeper, high and low freq, say... less than 50 ohms low freq, less than 5 ohms, higher freq.
some sort of adjustable sample averaging, so adjustable resolution vs speed.
i'd consider removing the rotary switch, possibly free up some front panel and internal space, i wish there was a nice way to be able to have the meter "saved" in a mode, so when you turn it on/off/on it is still in the same mode - this also fixes the issue of default turn on mode.
i'm sure inductor measurement could be done fairly simply, i do agree basic ballpark inductance would be an excellent addition to most multimeters.
weight isn't really an issue, size is only somewhat of an issue too, i mean, there is a fairly large range of acceptable sizes of multimeter.
i think AAs are the way to go though, i'd be fine with even a ridiculous number of them too, say 8, simply because they're common and relatively energy dense and cheap, also, if you have 8 AAs in series, you cut down on the boost converters for backlights, diode tests, amplification ect



I do agree though, community would kill progress on something like this. Compromises are fine, provided you're compromising the right things.