Sciencemadness Discussion Board

Anyone use a multimeter/voltmeter with USB/PC output?

RogueRose - 22-1-2019 at 21:03

I've been doing a lot of work with electronics and electrochemistry and it would be REALLY nice to be able to record data from a multimeter such as voltage, temperature, resistance and current - for different projects.

Some of these reading would need to be a continuous readings like every second or so (or on timed interval) where I can later plot out the graph of the reading vs time.

Other needs are for doing large batches of readings for things like batteries, each uniquely labeled/ID'd, and recording voltage & reistance,

I'd LOVE to have something that can either support multiple temp probes/thermocouples or multiple voltage readings but I don't want to break the bank. I've been looking into arduino's and their ability and it seems like this might be an area where these things could be useful, though I haven't really used these yet.

Does anyone have any suggestions for off the shelf multimeters that are a decent value? I'm extremely surprised that none of the Fluke meters I've been looking at have USB/RS232 output as standard (especially for $300-600!). I'm not looking to spend that kind or dough but find these models at auction from time to time, so I take a look at specs and price.

wg48 - 23-1-2019 at 02:19

I agree a pc interface on a multimeter would be super useful. I have looked for a cheapish one without success too. Given how little additional cost it would be these days its surprising that there is not one available or at-least I have not found one if one is available. Preferably one with a thermocouple input.

An option I considered is replace the IC of a MM with a precision AtoD and an Arduino with an optoisolated USB connection or just add the Arduino, with a USB and have the Ardiuno read the display interface of the multimeter.

PS I searched agaiin and found several here is one https://www.ebay.co.uk/itm/Multimeter-with-USB-interface-Pre...

Many more are available ranging from £40 to £200+. I guess they recently realised its a cheap addition to add significant value. I am reasonable certain I searched for ones last year. Perhaps I used the wrong search terms.

Here is a super nice new one with a dual display RMS reading and under£40 (free postage) I want to order three of them LOL https://www.ebay.co.uk/itm/ADM20-RMS-Multimeter-and-Digital-...

I can not find the spec for it. I need a spec to part with £40.

PSS Just in case I missed them I searched for cheapish temperature controllers with USB but have not found any cheapish ones yet. I guess its only a matter time. It would not cost significantly more to have a WiFi/Bluetooth interface on a multimeter or T controller


[Edited on 23-1-2019 by wg48]

j_sum1 - 23-1-2019 at 03:16

You might search for an oscilloscope. It may be there is something out there that does exactly what you want. Maybe second hand even.

Sulaiman - 23-1-2019 at 05:54

Quote: Originally posted by wg48  
... its surprising that there is not one available or at-least I have not found one if one is available. Preferably one with a thermocouple input.
...
I can not find the spec for it. I need a spec to part with £40.

@wg48 : No actual specs. but an idea of the ranges;
https://www.aliexpress.com/item/Bside-ADM20-6000-Counts-True...
and a review
http://budgetlightforum.com/node/65324

Probably similar to the generic 6000 count IC based DMMs like my AN8002
Scale errors can be computationally eliminated and the repeatability of measuring my Weston cell is so far perfect (+/-1 digit)

I too looked about one year ago, my RS232 DMM got 'lost',
Imagine what will be available next year ... :P

@j_sum1 : a 'scope is illuminating but some things such as electrochemistry (e.g. V vs. mA.h) or energy harvesting are more suited to data-logging.

One problem with 'inteligent' DMMs (such as the Fluke that I used at work) is having to wait for your multimeter to boot and do a POST before you can check anything.
The meter also depleted 4x AA alkaline cells every few months.

Also, I'm not sure how much I'd trust the insulation/isolation so consideration of potentials connected to should be made.

[Edited on 23-1-2019 by Sulaiman]

andy1988 - 23-1-2019 at 06:17

Quote: Originally posted by RogueRose  
I've been doing a lot of work with electronics and electrochemistry and it would be REALLY nice to be able to record data from a multimeter such as voltage, temperature, resistance and current - for different projects.

Some of these reading would need to be a continuous readings like every second or so (or on timed interval) where I can later plot out the graph of the reading vs time.

Good question. I've found the EEVblog to be a great resource:
https://www.eevblog.com/forum/testgear/multimeter-spreadshee...

The EEVblog users have grave concern about using <$100 USD multimeters for touching mains electricity, they talk about safety specs. So, maybe that is one reason many of these models are more expensive.

I've spent years dealing with all sorts of such instruments in a past job, characterizing sensors/systems. I suggest recording time as unix time so it's easily sorted and with minimal overhead in the database; as whole seconds in an unsigned integer, with milliseconds or microseconds in a separate integer field, don't use floats, don't use the database provider's non-standard datetime constructs (they all have their own extensively documented solution full of bugs and other crap).
Quote: Originally posted by RogueRose  
Does anyone have any suggestions for off the shelf multimeters that are a decent value? I'm extremely surprised that none of the Fluke meters I've been looking at have USB/RS232 output as standard (especially for $300-600!). I'm not looking to spend that kind or dough but find these models at auction from time to time, so I take a look at specs and price.

Quick advice (certainly not optimal, I've not explored all options, try posting on EEVblog with your use-case):
UNI-T UT61C (~$42 USD) if you want thermocouple in DMM (has limitation of 230C?).
UNI-T UT61E (~$35 USD) without thermocouple feature (a bit cheaper on ebay), may as well have an ardunio/microcontroller handle a MAX6675 based thermocouple.
Manual. UT61C RS232/USB cable may have some unique chip on it or a non-standard connector (~$8)? UT61E has different cable?.

Never use either of these models to touch mains electricity, a lethal shock may result!

I'm not sure if the protocol allows switching between voltage and resistance measurement, or if the hand dial must be manually turned. I know with benchtop multimeters you can remotely change the mode, not sure about handhelds.
Quote: Originally posted by RogueRose  
I'd LOVE to have something that can either support multiple temp probes/thermocouples or multiple voltage readings but I don't want to break the bank. I've been looking into arduino's and their ability and it seems like this might be an area where these things could be useful, though I haven't really used these yet.

If the sample rate on the device is fast enough, I expect you could electromechanically multiplex multiple probe sets to a single DMM (digital multimeter), like with a couple 8 channel relays. Crazy idea, I'm no electronics expert, but the thought came up as it would be cheaper than multiple DMMs. How many signals you multiplex would depend on the DMM sample rate [1] and your requirements. You'd use the microcontroller to change the relays to the probes you want, consider the relay delay, and algorithm the DMM uses (e.g. a remote measurement command may send a cached average of multiple past measurements, or command a new average to be measured, etc). I'm thinking banana plug probes (or this) and sockets.

In the past I did have an opportunity to buy a bunch of these rs232 handheld DMMs for $1 each, but I took a pass after seeing their max remote measurement rate was only 1Hz (probably as a means to upsell another of the company's products).

Again, may be better to get a standalone rs232 thermocouple thermometer (aforementioned microcontroller+MAX6675) as then you could measure temperature as well as a voltage/resistance/current measurement concurrently. I don't know of any nice "plug and play" opensource hardware/software thermocouple projects off the top of my head, but I'm sure at least one exists somewhere (like this?).

I'm not fond of batteries in the handhelds. Personally I'd be look into on soldering a 3V power supply to one of these handhelds, but I'm guessing an isolation transformer may be necessary if you ever used one on something touching mains. Also not sure if their circuit design depended on the batteries somehow (IIRC it does). So I could log data for days/weeks and not worry about loosing data... looks like Sulaiman also mentioned this.

[Edited on 23-1-2019 by andy1988]

Heptylene - 23-1-2019 at 06:19

You could go with an Arduino + SD card datalogger modules (these already exist, just plug and play). You can then plug whichever sensor you want in the arduino and record the data to the SD card. Sensors such as thermocouples, voltage and current sensors are easy to find

I'm actually also interested in that kind of datalogging capability. I'd like to measure the current and voltage of a chlorate cell to know exactly how much energy it consumes over a given run, to be able to calculate the electrical efficiency.

andy1988 - 24-1-2019 at 12:26

This capability is certainly among my interests, an a subgoal of my goals (sodium sulfur battery & PV array), so I will work on a solution with you. Even going as far to make a session manager, in smalltalk, with web interface for visualization of data.

An open source session manager with nice bells & whistles. I'd made a couple generic session managers myself... for former companies/organizations. SCPI though (which pretty much every modern benchtop DMM use), unclear if it will handle an ASCII protocol like I expect with inexpensive handhelds.
Existing Sigrok frontends may be worth looking into. EDIT: Command line example with plotting.

More DMM options:


EDIT: A nice DMM feature/spec visualization/compare tool (hover mouse over model to see specs/features).
EDIT: A thread on usb/RS-232 and isolation, also bluetooth. Says some multimeters not isolated properly, and may negatively influence the measurement or even risk damaging the computer.

In regards to further inexpensive handheld DMM concerns:


I've read through a bunch of RS-232 and bluetooth "hacks", they don't seem to be worth the effort (low sample rate), and no way to remotely change measurement mode. Mooshimeter seems to match my wishlist the best (opensource too!), but certainly a modified AN8008 would be cheaper. I'd not yet considered other specifications, like measurement range, and hadn't looked into inexpensive benchtop units.

I did see the BK precision 5492b (benchtop unit) has a sample rate of 25Hz. Others are significantly faster. I'll keep searching EEVblog, but this is enough search for today.
Quote: Originally posted by wg48  
PS I searched agaiin and found several here is one https://www.ebay.co.uk/itm/Multimeter-with-USB-interface-Pre...

Looks like this one, some brandings are discontinued, others still available, and the remote communication gets unstable long before the low battery indicator appears!

[Edited on 25-1-2019 by andy1988]

Ozone - 24-1-2019 at 12:47

I have successfully used (an older model, IIRC $60US) these to log V, A, T°C, etc. They are single channel only, and poll at 1 Hz (or less), but for the money, the interfacing works well:

https://www.amazon.com/RadioShack-46-Range-Digital-Multimete...

O3

Twospoons - 24-1-2019 at 14:06

I have a Keysight multimeter with an isolated PC interface, but that cost me NZD400 (~USD250) so probably a bit pricey for you.
Have you looked at the range of sensor modules from Phidgets

I've used their relay modules for some automation work, it was pretty easy to get going in C# - they have good documentation.

RogueRose - 25-1-2019 at 00:39

Wow, This is some awesome data!

I like the idea of the multiplexer especially if I can use a device with a high sampling rate. I found a unit which I might be able to get for a decent price (fingers crossed - surplus auction) that is 25 Hz, it is a BK Precision 2831 E

http://www.bkprecision.com/products/multimeters/2831E-4-1-2-digit-true-rms-bench-digital-multimeter.html
Manual for 2831 E

Datasheet for 2831 E

If I can get this unit for a good price then I think a lot of my problems will be solved but I'm still interested in looking into a custom arduino setup for temp monitoring, and the SD option seems like a possible solution.

wg48 - 25-1-2019 at 01:27

andy1988: Thanks for that info. The open source session manager looks super interesting. Last year I searched for something like it to control an arduino PID, ramp and soak temperature controller.

Unfortunatly I can not run the session manager on this old (vista) computer so I have not been able to try it out yet. I want to know how difficult it is to use for my DIY arduino project as my programming skills are limited.

When you refer to your smalltalk sessionmanger is that just a front end module to add to the session manger for your particular application?
More particularly is a front end module needed for each instrument or is there an existing one sufficiently flexible to only requiring a usb connection to an arduino?

[Edited on 25-1-2019 by wg48]

wg48 - 25-1-2019 at 02:15

Quote: Originally posted by Heptylene  
You could go with an Arduino + SD card datalogger modules (these already exist, just plug and play). You can then plug whichever sensor you want in the arduino and record the data to the SD card. Sensors such as thermocouples, voltage and current sensors are easy to find

I'm actually also interested in that kind of datalogging capability. I'd like to measure the current and voltage of a chlorate cell to know exactly how much energy it consumes over a given run, to be able to calculate the electrical efficiency.



For a stand only solution and low cost that is attractive depending on how easy it is to select which data is logged and when.

I would prefer a pc interface for on the fly control and data storage. Hopefully the session manager suggested by andy1988 is suitable and not too difficult to configure and use with arduino.

Something I was intending to post in the current sensor thread was a V,A, power and energy meter with a USB interface for £20. I think it was on Banggood. Perhaps it would be useful ready to go solution for you.

Sorry I cannot find the power meter now.

[Edited on 25-1-2019 by wg48]

andy1988 - 26-1-2019 at 10:31

Quote: Originally posted by Twospoons  
Have you looked at the range of sensor modules from Phidgets
Those are neat, I love the modularity.
Quote: Originally posted by RogueRose  
I like the idea of the multiplexer especially if I can use a device with a high sampling rate. I found a unit which I might be able to get for a decent price (fingers crossed - surplus auction) that is 25 Hz, it is a BK Precision 2831 E

If I can get this unit for a good price then I think a lot of my problems will be solved but I'm still interested in looking into a custom arduino setup for temp monitoring, and the SD option seems like a possible solution.
Certainly. I will go with the Mooshimeter, and I'll pick up a benchtop DMM if I see a good deal like you did. Though I'm not keen on the SD card if it's all on the bench, it's a chore for me to pull data off an SD card, then process into database, I prefer to store straight to computer in possible interactive session. SD card would make sense for non-benchtop or remote work.

My plan for multiplexer:

For the micro-controller on the multiplexer, I'm thinking a PSoC 4200M for $10 USD, Male Header Strips for ~$1 USD, and breadboard wires to link GPIO pins to the relays.

Could be operated while plugged into a usb port, or operated off of battery or powersupply, and communicate via Bluetooth LE. I'm choosing a PSoC because it is impressive hardware (I want to get into FPGAs with this platform later), but there may be no hand-holding or existing libraries like with arduino but debugging problems appears to be superior. Just using GPIOs here and I want the Bluetooth LE.

EEVblog thread on buying test lead cable. <$1/meter for 18AWG tinned copper silicone insulated. Then appropriate cable terminals, IDK which ones are appropriate for the relays & 18AWG yet.

Bluetooth LE usb for $1.62. Communicating over bluetooth is easy, it is just like serial communication over RS-232, and no worries about frying a part of your laptop accidentally. On linux use /dev/rfcomm0 device file just like you would a serial port (with setup nuances).

Algorithm would be:
  1. Loop
  2. TX DMM measurement.
  3. RX DMM measurement.
  4. TX PSoC change relays to probes for next measurement.
  5. Delay for relay to change (find delay through experiment)
  6. End Loop
Certainly cheaper to multiplex than buy additional DMMs (with feature/specs required). Now that I think about it I don't think I need this for the sodium sulfur batteries, but useful tool to have in the toolbox anyway.
Quote: Originally posted by wg48  
The open source session manager looks super interesting. Last year I searched for something like it to control an arduino PID, ramp and soak temperature controller.
Agreed! I know of nothing else open-source, labs seemed to all have their own in house solutions. Colleagues saw one in a lab at Purdue, then asked me to make one in an open-ended wishy kind of way. I made two approaches (the latter better platform). But I was torn down busy with school, life, and never finished my conception of what it should be :( I did integrate scripting language though, with APIs algorithmically made for the instrument in question (from SCPI syntax). The calendar feature is nice.
Quote: Originally posted by wg48  
I want to know how difficult it is to use for my DIY arduino project as my programming skills are limited.
Intuitively should work fine, the author has a screenshot of a javascript script made in the program. Script should open connection(s), do stuff, log to database, then close connection(s). Look at the script as describing what the instrument(s) should do/record during an experiment? Regarding the arduino/PSoC microcontroller not implementing SCPI protocol over serial, the session manager should work just fine, it will just TX and RX strings to the instrument just the same.

Benefit of using that session manager is the calendar, notes, management of sessions with multiple instruments, front-end for scripting, and database integration. The waveform and protocol UI wouldn't make sense for arduino/PSoC, unless SCPI protocol were implemented in the microcontroller's code and said instrument protocol defined in the session manager software. SCPI protocol is useful, at least *IDN? is something I suggest as diagnostic (e.g. if you connect to COM1 on windows, write *IDN?, it will say "I'm Instrument XYZ"). Other useful commands like *RST you can read about in any SCPI instrument manual which describes what commands they implemented. Not difficult at all, SCPI is just how the communication is organized. Transmitting a ? at the end of the string means it's a query and it should respond.

I assume just the the TX and RX strings are logged to the database, with timestamps. For custom database tables (e.g. {time,volt1,volt2,volt3,amp1}) you'd need to define said tables explicitly, in the script or wherever, and insert to said table within the script. Or just append experiment data to a CSV file as that's a bit easier.

Oh, the plots you see in the author's screenshots of the session manager are waveforms, binary data sent by the instrument (probably a scope, logic analyzer or whatever). What happens is a plain text SCPI query is sent to the instrument, then the instrument responds with a blob of binary data representing the waveform.

To get nice plots for our custom arduino/PSoC instrument or DMM we'd query the relevant x/y data from the database (or CSV file if you did it that way) we logged to in the experiment's script and plot them with whatever software.
Quote: Originally posted by wg48  
When you refer to your smalltalk sessionmanger is that just a front end module to add to the session manger for your particular application
I'll probably just use their session manager instead of making one now that I'd thought more on it... and do my own stuff as need arises.
Quote: Originally posted by wg48  
More particularly is a front end module needed for each instrument or is there an existing one sufficiently flexible to only requiring a usb connection to an arduino?
Looks like in his software there must be a definition for an instrument. He briefly describes the process to define an instrument here. Shouldn't be hard to stick a blank one in there, no SCPI protocol, just name it arduino, connection on COM1 or whatever. Oh, may have to make the arduino respond to the *IDN? query, I assume his software depends on that. He does have a 'Generic' instrument pictured here, mentioned here.

EDIT: Oh, yes, in your case in the GUI an instrument widget would be made for each of "arduino PID, ramp and soak temperature controller". The latter two might use SCPI.

I realize I may have left gaps in logic, if anything doesn't make sense feel free to ask questions. I'll try to order the stuff soon and build this multiplexing gizmo :)

[Edited on 27-1-2019 by andy1988]