Pax Instruments MultiLogger

[charlespax]

Now that the T400 is rolling along, I've been kicking around the idea of making an open source multimeter. I'm a bit reluctant to do this because there are already a number good quality and affordable multimeters out there. If I were to do this, it would have to be something very unique and not just another standard multimeter.

When I think of the term "multimeter" I think of a device that can measure the instantaneous value of one of several possible value types. Multimeters generally measure voltage, current, and resistance. Some multimeters can also measure frequency, temperature, duty cycle, and other parameters. There are some multimeters that can log data, but most only show you the instantaneous value you are measuring.

There are many situations where measuring a parameter over time is indispensable. Doing this by hand is often laborious or impractical. The difficulty increases in cases where multiple parameters must be measured over time. Maybe I'm thinking of something that should be called a "multilogger." This is the area I'm most interested in.

I'd love to have some input about what your use cases are and hat problems you have been trying to solve and been fumbling around with multiple multimeters and writing down data.

I'd appreciate it if you would provide a short description of the project you're working on and describe the parameters you would like to measure.

(original post)

[stmdude]

What I could really need is a DMM that works more in the time-domain.

My problem:
I make devices that uses a very small amount of power (operates years on a coin-cell).
This means that the device spends most of its time sleeping at ~1uA, with periodic wakeups that last <10uS
Now, to get an idea of how long the device would last on a battery, I usually hook it up to a 6.5 digit bench DMM, and log the crap out of it. However, since the update-rate on even expensive DMMs (34410A being used) is quite low at these currents (~10Hz), it will miss a lot of the wakeups.
Right now, I compensate with statistics, I.e, I run it for 1+ hours to make sure I get a proper average..
This takes time out of the development cycle, and would make automated power-measurements quite expensive (racks of 34410As or 34450As aren't cheap).

If I could get a DMM that measures faster (20Hz for instance) at these currents, it would cut my test-time in half..

An Oscilloscope would be a solution, but their dynamic resolution (voltage wise) aren't nearly good enough  (~1uA in sleep, ~10mA when RFing).

One could go about this in the regular multimeter way, but another way could be to charge a cap, drive the "load" off of that for a time-period, and then measure the remaining charge in the cap. Kind of a reverse sample-and-hold situation.

Apart from that, having a multimeter that can log over BLE (for example) would be nice for testing in temperature-chambers, acoustic chambers and the like.

[danadak]

On several occasions I have wanted a capable data logger, like when I repair
instruments and having power supply issues, like startup for example. By
having a logger that could capture startup kinds of speeds, 1 mS or better
sampling rate, over several days to find an intermittent in a cap, device.....

Modern DSO could have been used but they are limited on data capture over
long periods.

Another attribute that would be nice is a V source (low current, mA) and a
current source. Modern power supplies can function like this, but they have
low resolution in their settings.

A differential mode for measurements......

Regards, Dana.

[charlespax]

What I could really need is a DMM that works more in the time-domain.

My problem:
I make devices that uses a very small amount of power (operates years on a coin-cell).
This means that the device spends most of its time sleeping at ~1uA, with periodic wakeups that last <10uS
Now, to get an idea of how long the device would last on a battery, I usually hook it up to a 6.5 digit bench DMM, and log the crap out of it. However, since the update-rate on even expensive DMMs (34410A being used) is quite low at these currents (~10Hz), it will miss a lot of the wakeups.
Right now, I compensate with statistics, I.e, I run it for 1+ hours to make sure I get a proper average..
This takes time out of the development cycle, and would make automated power-measurements quite expensive (racks of 34410As or 34450As aren't cheap).

If I could get a DMM that measures faster (20Hz for instance) at these currents, it would cut my test-time in half..

An Oscilloscope would be a solution, but their dynamic resolution (voltage wise) aren't nearly good enough  (~1uA in sleep, ~10mA when RFing).

One could go about this in the regular multimeter way, but another way could be to charge a cap, drive the "load" off of that for a time-period, and then measure the remaining charge in the cap. Kind of a reverse sample-and-hold situation.

Apart from that, having a multimeter that can log over BLE (for example) would be nice for testing in temperature-chambers, acoustic chambers and the like.

(Just me thinking...) Okay, so characterizing the power consumption of devices that draw low power and have power spikes. I can see how high frequency measurement would be important. A 20 Hz rate is certainly doable. I wonder how a coulomb counter feature would compare against measuring voltage and current individually. SparkFun has a nice coulomb counter post.

[Jeroen3]

One that can measure power or phase would be nice. Those are rare.

[prasimix]

Don't know if that is count as standard feature but I'd like to measure L, C and eventually ESR.

Another thing: MCU that has enough flash (min. 512K) and SRAM (64K or more) that e.g. SCPI remote control can be added in one moment.

[charlespax]

On several occasions I have wanted a capable data logger, like when I repair
instruments and having power supply issues, like startup for example. By
having a logger that could capture startup kinds of speeds, 1 mS or better
sampling rate, over several days to find an intermittent in a cap, device.....

What sorts of things are you measuring during startup?

[stmdude]

Another thing: MCU that has enough flash (min. 512K) and SRAM (64K or more) that e.g. SCPI remote control can be added in one moment.

Holy crap. What are you planning on putting in there?  I can fit an RF stack, an RTOS, a CLI, SPI-code, and a crapload of logic into a 64/16 MCU, with more than half of the flash and RAM free for expansion.

But, different people want different things and tools. I don't know if Charles has a favourite MCU in mind?  Maybe they have pin&code compatible variants, so people could upgrade their MCU ?

[charlespax]

But, different people want different things and tools. I don't know if Charles has a favourite MCU in mind?  Maybe they have pin&code compatible variants, so people could upgrade their MCU ?

Right now I'm digging the STM32F103Rx series. In that family and package ST has a wide range of flash sizes from 16k up to 1024k. My experience with the ATmega32U4 taught me that when you need a little more programming space it's better to spend money on a high capacity chip than spend money on developers. It really sucks to spend heaps of time and money optimizing code just because your code compiles to 33k insteadk of 32k.


GigaDevice is a Chinese company that makes a series of ARM chips that are pin-compatible with ST chips. They don't cover ST's entire catalog, but do cover some important families. I understand GigaDevice licenses the ARM core and peripherals and just makes their chips register and pin compatible. They even have the same naming scheme (e.g. GD32F103). This allow me to effective have two manufacturers for the same chip. Second sourcing is wonderful    Additionally, GigaDevice carries the GD32F103Rx in 2048k and 3072k versions. Talk about headroom! It's like the chip-level version of Arduino and Freeduino etc..

I can see a device running FreeRTOS for the core software and having MicroPython or Espruino run as a low priority task. The core system would be nice and snappy while the interpreter could run user code without affecting core functions.

[bitseeker]

Hi Charles,

Here are some logging issues I've run into:

1. Testing power supplies. Simultaneously measuring voltage and current stability over time with and without a load. Currently using two bench DMMs (one for V, one for I). I have a multichannel logger, but it's V-only. I also use a scope for checking transient response during turn-on/off. It'd be nice to be able to consolidate these disparate data sources and even do it for multi-channel power supplies.

2. Testing/adjusting oscillators, function generators. Measuring frequency and phase between two sources for alignment and stability over time. For example, adjusting an OCXO to a GPSDO source or verifying phase stability of a mutli-channel function generator.

3. I don't current have need for this, but I could see factoring in ambient and/or enclosure/component temperature data along with the data in #1 and #2.

[bitseeker]

Oh, as a side note, having to log via a blend of GPIB, Ethernet, USB, and serial interfaces is...challenging.

[stmdude]

But, different people want different things and tools. I don't know if Charles has a favourite MCU in mind?  Maybe they have pin&code compatible variants, so people could upgrade their MCU ?

Right now I'm digging the STM32F103Rx series.

They're good mid-range devices for sure. Pin-compatible to a large extent, except that you only get (for example) DAC functionality on the high-density devices.
But, it will allow you to start with a 512KB flash device for development, and then cost-optimize down to 384 or 256 depending on how big your code ends up. Only manufacturer that does that afaik.

Done know about which peripherals the GigaDevices MCUs have though. As in, are they compatible with a low, medium or high-density STM32F103 ?

I can see a device running FreeRTOS for the core software and having MicroPython or Espruino run as a low priority task. The core system would be nice and snappy while the interpreter could run user code without affecting core functions.

That would work. Don't know which language would be the most compatible with EE guys though. There are tiny JavaScript interpreters as well as LUA to consider.

[Marco]

Now, to get an idea of how long the device would last on a battery, I usually hook it up to a 6.5 digit bench DMM, and log the crap out of it. However, since the update-rate on even expensive DMMs (34410A being used) is quite low at these currents (~10Hz), it will miss a lot of the wakeups.=

Doesn't it do 1 ks/s at 6.5 digits?

PS. you of course need to low pass the current somehow to make sure you don't miss short events, a large enough (super-)capacitor in parallel with the load so that together with the shunt resistance it low passes the current to 500 Hz should do it.

[ataradov]

I make devices that uses a very small amount of power (operates years on a coin-cell).

I came here to type basically  the same thing, so major +1. A tool for low-power profiling would be awesome.

[charlespax]

Done know about which peripherals the GigaDevices MCUs have though. As in, are they compatible with a low, medium or high-density STM32F103 ?

Datasheet is attached with relevant GD32F103 peripheral tables.

[trevwhite]

What I could really need is a DMM that works more in the time-domain.

My problem:
I make devices that uses a very small amount of power (operates years on a coin-cell).
This means that the device spends most of its time sleeping at ~1uA, with periodic wakeups that last <10uS
Now, to get an idea of how long the device would last on a battery, I usually hook it up to a 6.5 digit bench DMM, and log the crap out of it. However, since the update-rate on even expensive DMMs (34410A being used) is quite low at these currents (~10Hz), it will miss a lot of the wakeups.
Right now, I compensate with statistics, I.e, I run it for 1+ hours to make sure I get a proper average..
This takes time out of the development cycle, and would make automated power-measurements quite expensive (racks of 34410As or 34450As aren't cheap).

If I could get a DMM that measures faster (20Hz for instance) at these currents, it would cut my test-time in half..

An Oscilloscope would be a solution, but their dynamic resolution (voltage wise) aren't nearly good enough  (~1uA in sleep, ~10mA when RFing).

One could go about this in the regular multimeter way, but another way could be to charge a cap, drive the "load" off of that for a time-period, and then measure the remaining charge in the cap. Kind of a reverse sample-and-hold situation.

Apart from that, having a multimeter that can log over BLE (for example) would be nice for testing in temperature-chambers, acoustic chambers and the like.

Some meters have an integral based current measurement. They use a PLC setting. So say you set it to 1 second it will integrate total current over that second. This might help with average current measurements. It works well on my Keithley 2110. I tested it with a 1ms current pulse over 1 second and it measured average current nicely

[charlespax]

I came here to type basically  the same thing, so major +1. A tool for low-power profiling would be awesome.

What kind of resolution do you need in terms of time and voltage? Would it be sufficient to use a coulomb counter that gives resolution of 0.1707mAh?

[stmdude]

Done know about which peripherals the GigaDevices MCUs have though. As in, are they compatible with a low, medium or high-density STM32F103 ?

Datasheet is attached with relevant GD32F103 peripheral tables.

Seems like the GD32F103 Tx, Cx, R4->B, V8, VB would correspond to the STM32 Medium-density devices.
GD32F103 RC->RK, VC->VK would correspond to the high/xl-density devices.

As for STM32F103: 
STM32F103x4/x6 are low-density devices.
STM32F103x8/xB are medium-density devices.
STM32F103xD are high-density devices.
STM32F103xF/xG are XL-density devices.

[stmdude]

Some meters have an integral based current measurement. They use a PLC setting. So say you set it to 1 second it will integrate total current over that second. This might help with average current measurements. It works well on my Keithley 2110. I tested it with a 1ms current pulse over 1 second and it measured average current nicely

Oh, nice. How does it deal with dynamic range?  As in, my device sleeps at ~1uA, and then "every now and then" transmits RF, and jumps to ~13mA (for <10uS). The 6.5 digit range on the 34410 doesn't like that, and wants to switch ranges on me (unless I shove a big old cap in parallel to take the edge off).

I've been eyeing a 8.5 digit DMM, but I can't really justify the cost..

[trevwhite]

Some meters have an integral based current measurement. They use a PLC setting. So say you set it to 1 second it will integrate total current over that second. This might help with average current measurements. It works well on my Keithley 2110. I tested it with a 1ms current pulse over 1 second and it measured average current nicely

Oh, nice. How does it deal with dynamic range?  As in, my device sleeps at ~1uA, and then "every now and then" transmits RF, and jumps to ~13mA (for <10uS). The 6.5 digit range on the 34410 doesn't like that, and wants to switch ranges on me (unless I shove a big old cap in parallel to take the edge off).

I've been eyeing a 8.5 digit DMM, but I can't really justify the cost..

I set my 5.5 digit meter to 100ma range and it did the rest. Its an analogue measurement technique so I have a feeling it will handle things. Possibly if signals are extremely quick it might struggle but seriously I do wake up and sleep stuff and before I found the integral feature average current was a nightmare. Now it is easy

[charlespax]

For hardware, I'd like to reuse the T400 enclosure if possible since I already have the tooling. The top panel is interchangeable and can be replaced with a 1.6 mm PCB. There are six buttons, a MicroUSB connector, MicroSD card connector, and a 132x64 pixel LCD.

I'm wondering what everyone thinks of the landscape layout versus a traditional portrait style hand-held meter. Personally, almost always use my DMMs when they're sitting on my bench rather than held in my hand. It can be frustrating to shuffle things around on a bench and knock over or nearly knock over a multimeter. I made my temperature data logger in a landscape format to keep it nice and stable. Pulling on a cable just drags it along a bench instead of tipping it over. I wonder how suitable this format would be for a multimeter. If you want to take a closer look at the enclosure, check out the github repo https://github.com/PaxInstruments/t400-enclosure. How do you feel about this form factor?



Since the front is mostly screen it doesn't really fit a traditional range switch. Function selection could be done with software buttons or maybe slider switch.

Would a landscape design be crazy, awesome, or something in between?

[ajb]

Some way to synchronize and time-correlate multiple units would be nice.  Could be as simple as a trigger in/out, or something more sophisticated to facilitate easy master/slave configurations when you need to log across multiple channels.  The latter is less compelling if you're intending this to be automated via PC, but for standalone use being able to pull logs from multiple units through one interface would be nice.

[ataradov]

What kind of resolution do you need in terms of time and voltage? Would it be sufficient to use a coulomb counter that gives resolution of 0.1707mAh?

I don't know what technical implementation would be the best. So let me describe how I do it right now. Typical things I work with will sleep and consume ~2.5 uA, at wake up power consumption is very dynamic and goes up to ~20 mA, but with very variable profile. Wake up duration is 5-20 ms. I'll attach some pictures later.

Right now I do high resolution (in the time domain) captures of a voltage drop over 10 Ohm resistor. This gives me a representation of the active current consumption that I can integrate. I identify all possible wake up scenarios, capture a representative sample of all of them and do my battery estimations based on the sleep current (measured with a DMM) and number of events and expected power consumption during that event.

This is a time-consuming process, but I found the accuracy good enough.

Resolution of 0.1707mAh will be more than sufficient, but what about the accuracy?

[stmdude]

Would a landscape design be crazy, awesome, or something in between?

Landscape works fine on bench DMMs. Should work fine, I'd guess. No need to plan a new tooling before trying what you have already.

As for the rest of the form-factor, I'm a little worried about the tippy-overness of it when connecting some decent banana-jack cables. They're not _super_ heavy, but the T400 doesn't look very hefty either.. 

I'm looking at https://github.com/PaxInstruments/t400-electronics/blob/master/eagle/T400%20Rev%200.14/PaxInstrument-T400.pdf ..
Seems like I could whip up an STM32 board that would fit in it quite quickly.  Won't do any multimetering, but enough to test the interaction.
Where does the battery connect?  Can't find it..
Would you mind sharing the part-numbers for the buttons and LCD connector?

[charlespax]

I'm looking at https://github.com/PaxInstruments/t400-electronics/blob/master/eagle/T400%20Rev%200.14/PaxInstrument-T400.pdf ..
Seems like I could whip up an STM32 board that would fit in it quite quickly.  Won't do any multimetering, but enough to test the interaction.
Where does the battery connect?  Can't find it..
Would you mind sharing the part-numbers for the buttons and LCD connector?

The battery connects on the back side of the PCB. You can see it in the attached image circled in red.


I've been planning on making a developer PCB with the processor, power, and all external interfaces populated on the PCB. Then there would be an empty area where a submodule could be soldered on. See the yellow area in the image below.



The LCD connector is a 12 pin 1 mm pitch FPC connector. It's a fairly standard footprint with many parts that fit it. The part number I use is FH12-12S-1SH(55). You can find a more detail conversation here.


The T400 tactile switches are generic ones, I don't have a specific part number. My PCBA house has suggested using more common square footprints that are more available. These can happily change.

[Marco]

High dynamic range, high temporal resolution current monitoring is a relatively specialized (but common) problem and doing it in the "normal" multimeter way requires too many compromises in my opinion.

I'd rather have a device which had two shunts in series, say 1 Ohm and 10K, with a very fast voltage clamp across the 10K resistor to limit burden voltage, low pass filters for the shunts and a couple MAX44252s to amplify the voltages by 100x (x10x10). That way you have two high bandwidth current measurements for two dynamic ranges which you can feed into a two channel scope, or a slower data-logger (with some extra low pass filtering most likely).

This kind of device makes more sense separate from a logger (there is more overlap with the uCurrent in fact).

[chickenHeadKnob]

I love the form factor of your T400! and having the probes come in at the top is very natural on the bench. If it is too tippy  as stmdude worries then perhaps make sure the stand hinge is at the very top of the case and have it open to an obtuse angle. You might have to modify the case but you should still be able to have a single case for both products. I don't particularly need or want another multimeter so I will let others guide you on specific features, however a few general comments come to mind:

• No point making an "also ran" that just copies other multimeter functionality. You already indicate you want to explore full time multi-channel. Great for measuring power,  if the other guys bench meters attempt this at all, they implement  it with relay kludge klackery.
• go for a high resolution ADC, 20 bits plus, because this is a bench machine. Select a delta sigma ADC for high resolution DC/low sample rate and offer two high speed 1Mhz sampling (or faster depending on processor) 12 bit channels connected  to the processor AtoD as stm32 have pretty good on chip converters, better than AVR I think. That way you can provide pocket DSO type inputs as well as exceed the typical multimeter specs. nobody else does exactly that, although to be fair the Keithley DMM7510 can run at high sample rate it also costs 4K$ If you provide fast inputs beware of the sustained through-put requirements for logging to USB storage or PC!
• As to processor selection I like the stm32 product line, however the stm32f103 does not come to mind as the first choice for a battery powered device. Entry level cortex M4F devices like Stm32f401 or '410 are  nearly as cheap and have very good power per mip especially when moderately underclocked at 32 to 20 Mhz. STM32l476 is intended for battery power and has nice power down/ wake-up modes but a cost premium
• color LCDs are becoming very cheap now, even cheaper than the older graphical mono displays, and I prefer them however I did not check on power consumption. Since you already have a display and the software to drive it probably doesn't make sense to upgrade.

While I am not in the market for a multimeter, I did look at your T400 and said "I wish Charley would make a 4 channel wheatstone bridge input version of this, with low voltage AC or pulse excitation and the requisite tables and formulas for resistive  temperature sensors like platinum RTDs and cheap ntc, ptcs"

[bitseeker]

Landscape is good for this especially for displaying recent samples in a scrolling graph, just like the T400. The enclosure might end up too small in the end, but the back could just be replaced with a deeper cabinet. That would provide space for more electronics, connectors, etc. as well as be more stable on the bench.

[EEVblog]

For hardware, I'd like to reuse the T400 enclosure if possible since I already have the tooling. The top panel is interchangeable and can be replaced with a 1.6 mm PCB. There are six buttons, a MicroUSB connector, MicroSD card connector, and a 132x64 pixel LCD.

I'm not sure you'd have enough room to mount the deep shrouded banana jacks required and have traditional protection components and spacing.
Certainly not for multiple channels which is what would differentiate a product in this space.
A low voltage multi channel voltage and current logger with screw/phoenix connectors, sure. A traditional multimeter, likely not.

An old video:

[charlespax]

Resolution of 0.1707mAh will be more than sufficient, but what about the accuracy?

Not sure, I haven't really looked down the coulomb counter road. I'm just thinking of ways for determining power consumption that are cheaper than brute forcing it with high speed current and voltage measurements.

[Marco]

Not sure, I haven't really looked down the coulomb counter road. I'm just thinking of ways for determining power consumption that are cheaper than brute forcing it with high speed current and voltage measurements.

You can low pass the signal across a shunt before sampling. Average value of a low passed signal is the same as the average value of the input.

I'm not sure you'd have enough room to mount the deep shrouded banana jacks required and have traditional protection components and spacing.

Without LowZ you don't need a PTC and you could use an external shunt for high current measurements. That saves a lot of room.

[TiN]

Perhaps one thing to consider is to make units networkable (e.g. have RS485 or BT coming out, so multiple units could talk to each other to combine data).
My use scenario for multiple channels are usually 2-3 channels for voltage monitoring (using bench 7.5-8.5d DMMs) + current monitoring (SMU) + 2-3 channels RTD sensors (other bench DMM and TEC SMU). There is not much you can do  in such a small case, so that's why the idea to make them expandable, with each meter have only one or two channels.
You can even have few versions of them, dedicated to more specific application (e.g. voltage high-resolution version or high-speed version).

As for ADC, TI ADS1262 is pretty capable cheap device. It have integrated current sources, temp sensor, multiple channels, easy to interface, and goes in solderable TSSOP. I had done a review on it's DK some time ago.

For energy meter there are some chips from AD in ADE series that can do power, factor and such measurements easily.

[charlespax]

I'm not sure you'd have enough room to mount the deep shrouded banana jacks required and have traditional protection components and spacing.
Certainly not for multiple channels which is what would differentiate a product in this space.
A low voltage multi channel voltage and current logger with screw/phoenix connectors, sure. A traditional multimeter, likely not.

A shrouded connector fits between the LCD and enclosure with just a few hairs to spare. With any luck, I can find a mating connector that mounts mid PCB. Another custom connector is probably not in the cards. I can say with high confidence that I will not be making any devices that measure mains voltage. Sticking to +/-12 V is fine with me. I'm not really interested in making a multimeter.



I hacked a PCB mount RF connector on one of my T400 devices. A screw on BNC adapter fits perfectly and looks pretty good. That could also be a connectivity option.

[EEVblog]

A shrouded connector fits between the LCD and enclosure with just a few hairs to spare. With any luck, I can find a mating connector that mounts mid PCB. Another custom connector is probably not in the cards. I can say with high confidence that I will not be making any devices that measure mains voltage. Sticking to +/-12 V is fine with me. I'm not really interested in making a multimeter.

In which case using shrouded meter leads is a bit pointless.
I don't think you can make this case into a multimeter, I don't see any market need for yet another (single channel) multimeter that can't be used on high voltage etc.
It should be a data logger, voltage and current, to match your temp logger. Logging usually means hooking up a semi-permanent test cable, so no point in using regular multimeter leads.

[EEVblog]

I hacked a PCB mount RF connector on one of my T400 devices. A screw on BNC adapter fits perfectly and looks pretty good. That could also be a connectivity option.

Bingo, a 4 channel high resolution scope type logger.

[Jeroen3]

Beware that you do not create fancy hardware with horrible software.

[charlespax]

stmdude whipped up a quick ARM PCB. We're working on basic hardware to get some momentum going and evaluate a few ideas. If you'd like to get your hands dirty working on the design, please join the discussion. This EEVblog thread will be for the more general discussion.

[sarepairman2]

I like the idea but choosing a spec to attain is the hard part.

I wanted to do this myself a few times, but I end up thinking.. do I want 2.5 or 4.5 digits on x-y-z range. what kind of voltage range is useful.... noise floor, update rate...

you can design 50 different systems all useful for something.. BUT HOW DO YOU CHOOSE A DESIGN??? 


and then.. how do you choose a design for sale? thats even harder....

this sounds useful for maybe green energy people... I think this would be a broader market then just electronics hobbyists. But then you might also want clip on measurement.

Alot of people are interested in temperature trends. Not so many people are interested in electrical trends. For AC power logging these is alot of options already. Not to mention the dangers of designing this stuff.

It seems that quite a bit of green sources make reasonably low voltage things appropriate for a meter that won't have CAT certifications and stuff. Also it would not make you crazy trying to design for nano ampers and stuff that hard core electronics people are interested in.

why can't it measure high frequency nanovolts???

This is assuming you want to make money. I have yet to design something to sell, only to satisfy personal curiosities.

From a hunch, if you want to sell near the price of the T400, which is 165$, with four channels, you won't be raising the bar in terms of any kind of measurements, making it difficult to appeal  to a volt/time/current nut, as cheap electronics have gotten precise enough that measuring drift is difficult.

A portable unit with its own batteries might be useful for drone power monitoring, green energy, MAYBE some automotive stuff (i don't know cars). Also maybe for monitoring the behavior of machinery like CNC machine/3d printer/etc, if it samples enough .

A bench top current logger without outstanding capability would probobly be relegated to measuring battery drain.. which you only need one channel for. And probobly a uCurrent to hook up to it  (business opportunity for a combo sale with dave jones lol). Plus lots of people are starting to get dummy loads now.

ANd selling something designed to hook into mains without the extensive safety testing just seems like a bad idea.

I have a FLUKE HYDRA DAQ.. I have yet to use it yet, and I have a fairly sophisticated interests... the main reason being that its resolution is not high enough to be useful to me.

Plus, for high speed measurement, there are tons of portable oscilloscopes out on the market. Not to mention regular bench top oscilloscopes are getting more and more channels cheaper, making it less and less appealing to have a separate unit.

What I don't see alot of is long term measurement devices that are light and have long lasting batteries.

I also think that the thing that people are asking for in this thread does not fit in with the marketing model that you have for your T400 (i.e. its useful for many many things, from bbq chicken to making moonshine vs its good for measuring power supply stability and battery drain). A big selling feature of your T400 is the data card.. a data card is not useful in a electronics laboratory when you are prototyping or repairing. It would just slow things down. It would only be useful for some kind of burn-in test but who is doing that? the mentality is "it works".

Using this forum for market research will contaminate your data with volt-nuts like myself

the last thing you want is "hackaday" to post a "hack" where you turn your oscilloscope time base wayyy down and plug a ucurrent into it to make a data logger instead of buying your product.

another interesting use for a data logger would be just general thing to connect transducers to, i.e. portable instrumentation package to put on a balloon/roof/mountain top/something

[charlespax]

A few of us have been hashing out a base design that will be used to experimenting with different measurement devices. The board has an STM32F103Rx microcontroller and all the essential components for interfacing with the T400 enclosure (LCD, buttons, MicroSD card, etc.).

There is a empty 32x66 mm space for soldering in a daughter board. The idea is to make a small batch of main boards, so we don't have to assemble the system core for each prototype. I think this will speed up instrument development.

I'm still laying out the board, but I thought you'd be interested in where things are. I'd love to have your feedback.

[Kean]

This looks great for some things that I had in mind for the extra enclosures I bought.  I was planning to probably use STM32F103 as well.
I don't have time right now to do my own layout as I'm in the middle of serveral other projects, but being able to use this with various daughter boards looks quite promising.
 

[charlespax]

I believe this first prototype revision is done. I'm going to sleep on it and order boards tomorrow. Please check out the code from https://github.com/PaxInstruments/labwiz-board and let me know if you have any feedback. You can post in this EEVblog thread, on the Pax Instruments forum thread or file an issue on Github. The schematic and layout are also attached.

[charlespax]

A lot of what we discussed is not all soldered up. Power is good. I still have to bring up the MCU.

I've going through the markets trying to figure out a good connector solution and I think I have one. In this photo you see a 12x2 half-height header with a 0.05 inch (1.27 mm) pitch. On the female side I can get custom bent legs that straddle a 1.6 mm PCB. The male connector fits nicely on a 1.0 mm PCB, but a 0.8 mm PCB might be better. I'll plug one of the holes, so the connector is keyed. Four of these will fit across the prototyping area with a one pin gap between and a bit on each side.

These two photos illustrate the size of a prototyping module. We could use up to four of these or just one big one. I'm really excited abouthis.

[danadak]

What sorts of things are you measuring during startup?


Basically power supply sequencing in embedded designs.


Regards, Dana.

[ataradov]

On the female side I can get custom bent legs that straddle a 1.6 mm PCB.

Where? If it is not a big secret. Those connectors are expensive as it is, I can't imagine customizations like that would be cheap.

[charlespax]

On the female side I can get custom bent legs that straddle a 1.6 mm PCB.

Where? If it is not a big secret. Those connectors are expensive as it is, I can't imagine customizations like that would be cheap.

Pretty much any factory that makes male/female pin headers can do it. Some things are really easy to do while other are hard. Things like pin length are pretty easy to change because it's a setting on the machine. Other things might be hard to do it the manufacturing process depends on that feature. I spoke with some factory people and they said this modification would not be expensive.

[charlespax]

Also, I'm pretty close to ordering the next batch of boards. Since these' some empty space I've added a few modules for testing. Three of them are for interfacing with the Seeed Studio Grove modules. This reduces the amount of time spent on hardware development and I can focus on writing code.

[Kean]

I'd be interested in getting a couple of the blank pcbs and assisting with debugging.  Please let me know if I can contribute.
I'm comfortable with doing my own assembly and not afraid of a bit of rework.  I probably also have many of the necessary parts in stock already, either from my other designs, or from the enclosure kits and mystery bags I got from you previously.

[charlespax]

I'd be interested in getting a couple of the blank pcbs and assisting with debugging.

That would be great! When I get boards back I will select one and solder down the minimum necessary components to verify the MCU can be programmed and there is no fundamental design error. I think it would be best to send you one in this configuration rather than a blank board. Otherwise, we run the risk of wasted money and time with shipping. How's that sound?

I can make a private item in the store and share a link here.

[Kean]

When I get boards back I will select one and solder down the minimum necessary components to verify the MCU can be programmed and there is no fundamental design error. I think it would be best to send you one in this configuration rather than a blank board. Otherwise, we run the risk of wasted money and time with shipping. How's that sound?

I'm happy with either bare or minimally populated boards.  Maybe just partially populate and quickly verify one for yourself, before shipping.
Even if there is a design error, I can probably work around it.  I've certainly screwed up my share of footprints in the past.

I can make a private item in the store and share a link here.

Good idea.  I'd love to grab two, but others here might also be interested depending on how many you're getting.

[charlespax]

I just ordered some boards from dirtypcbs.com. It's such a relief to get the hardware to this point. @protological has been crushing the firmware and has just about everything working in FreeRTOS.

Here's where we stand:

• STM32F103RGT6 microcontroller 1024 kb flash, 96 kb RAM
• Cortex debug has been working great with ST-Link and Eclipse
• Each module interface has CAN, i2C, USART, SPI, and GPIO
• There is extra space on the PCB, so I added three Seed Studio grove module adapters and one temperature module. The temperature module had an MCP9800 temperature sensor and an MCP3421 ADC for thermocouple input. This basically gives a single channel of what is in the T400. Having the grove module adapters will allow us to test hardware without having to develop and make boards right now.
• USB is configured as a virtual serial port and is working
• LCD is working
• The SD card is giving us a weird hard fault issue
• ESP8266 breakout header. Not tested.

[Kean]

Nice work Charles