Microammeter suggestions

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Hey all,

 

I am looking for a simple microammeter/millammeter that can measure up to lets say 2ma full scale.  I am trying to get an actual current draw of my entire circuit while the RF section is sleeping.  When everything wakes up I know its in the 200ma range, but that I do not care about.

 

I am looking at the ones from DROK, but I thought some freak might have another vendor recommendation.

 

Thanks

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Jim,

 

Have you heard of Dave Jones's "uCurrent"? (microcurrent)

 

https://www.eevblog.com/projects...

 

 

 

Ross McKenzie ValuSoft Melbourne Australia

Last Edited: Thu. Aug 30, 2018 - 01:57 AM
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That's a slick kit! Thanks. Will see if I can order one

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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jgmdesign wrote:
That's a slick kit! Thanks. Will see if I can order one Jim

 

Seems to be out of stock ?

Another approach could be to use the Current Monitor devices, which have a milli-volt current input, plus a volts input.

 

PAC193x

100 mV full scale range for current sense voltage, - 16 bit resolution
0V to 32V input common-mode voltage - 16 bit resolution for voltage measurements, 

 

eg  this for PAC1934 is in stock :

 

https://www.digikey.com/products...

 

or maybe this ?  (INA286)

https://www.digikey.com/products...

 

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The evaluation boards for Silicon Labs EFM, 8 range have onboard current monitors and there is a nice bit of software to read the data. I have seen a Web page where someone cut a couple of tracks to allow use with external chips.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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How much are you looking to spend?

 

Many low-cost handheld DMMs have uA ranges these days - I recently bought this one for this very purpose:

5XP-A - 600V AC/DC Digital Multimeter with VoltTect NCV

https://cpc.farnell.com/amprobe-...

 

It has a 200uA range ...

 

As Brian says, many dev boards now include some sort of "power analyser".

There's the Atmel "Power Debugger" - but that seems rather expensive for what it is.

 

Nordic's "Power Profiler Kit" is half the price: https://uk.farnell.com/nordic-se...

 

 

Do you just want to measure "static" current, or view the profile?

As I've mentioned before, I just use a current-sense amplifier (CSA) and scope ...

 

 

EDIT

 

Just remembered the SAML21 XPlained Pro board: http://blog.antronics.co.uk/2015/04/23/new-tricks-for-lower-power-from-atmel/

 

AIUI, its "Xplained Pro Analog Module "(XAM) is the "guts" of the Atmel Power Debugger.

http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42405-SAML21-Xplained-Pro_User-Guide.pdf - page 8

 

I don't know how hard it would be to "hack" the board to use this for measuring an external system ... ?

 

Currently fifty quid from Microchip: https://www.microchipdirect.com/product/search/all/atsaml21-xpro-b

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Last Edited: Thu. Aug 30, 2018 - 07:38 AM
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Like awneil #6 writes, uA ranges are pretty common with DMM's.

The Aneng AN8009 is a bit special in that regard. It is a 9999 count meter and it has an extra digit in a lot of ranges.

Current resolution is 100nA.

Voltage resolution is 1uV

Ohms resolution is 10mOhm.

The AN8009 is an USD 25 meter.

 

When measuring standby current of a uC it is handy if your meter can at least pass the full current (presumably 200mA) without too much voltage drop.

An easy way to do this is to put a (scottky) diode parallel to an external shunt resistor.

When the uC is asleep, the voltage drop over the shunt should be < 100mV and the diode conducts almost no current.

When the uC is active, the voltage drop over the shunt is limited by the diode (A few hundred mV).

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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Thanks for the diode tip - I will try that!

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Paulvdh wrote:
AN8009

This: https://www.amazon.co.uk/Digital-Ranging-Multimeters-Voltage-Electronic/dp/B07B6PLBK6 ?

Image result for aneng an8009

Trouble there seems to be that the uA measurement is on a different terminal from the mA and A ?

 

As you said:

Paulvdh wrote:
When measuring standby current of a uC it is handy if your meter can at least pass the full current (presumably 200mA) without too much voltage drop.

So that's probably going to be a problem with this one?

 

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valusoft wrote:
Have you heard of Dave Jones's "uCurrent"? (microcurrent)

jgmdesign wrote:
That's a slick kit! Thanks. Will see if I can order one
 

It's been mentioned a few times here. Might be worth searching out those threads - ISTR there were recommendations for other similar units ...

Who-me wrote:
Seems to be out of stock ?

The design is published - you could build your own ...

 

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Thanks for the diode tip - I will try that!

Indeed, +1!

 

Have you heard of Dave Jones's "uCurrent"? (microcurrent)

Jack Ganssle reviewed it a few years back:

http://www.ganssle.com/reviews/review_of_ucurrent.html

 

In that review he also mentioned:

https://www.electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhow

and:

http://www.keithley.com/data?asset=50390 (dead link, available via Wayback Machine):

https://web.archive.org/web/20140819113033/http://www.keithley.com/data?asset=50390

 

Others he has reviewed:

http://www.ganssle.com/rants/realtimecurrentmonitor.html

http://www.ganssle.com/rants/rtcm-version-2.html

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When buying a meter with a uA range you need to keep an eye on the 'burden voltage' spec. Or, in other words, the value of the shunt resistor used to measure the current. Some cheap meters can easily drop a few 100 millivolts which is not much good when your uC is running on 1.8V.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Brian Fairchild wrote:

When buying a meter with a uA range you need to keep an eye on the 'burden voltage' spec. Or, in other words, the value of the shunt resistor used to measure the current. Some cheap meters can easily drop a few 100 millivolts which is not much good when your uC is running on 1.8V.

That is the whole (or nearly) basis of Dave's design. Don't introduce a burdensome (forgive me please) burden voltage into your measurement setup.

Ross McKenzie ValuSoft Melbourne Australia

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So as not to burden myself with unecessary test gear I often made do with the stuff I had easily available. I.e. a simple R/C network inserted into the Vdd line. Although not shown in my schematic, either 10R OR 100R could be used. Oh and the electrolytic was low leakage.

I would connect a DMM for the static sleep mode currents and often scope the output when profiling the run mode current.

 

This does just fine for a "look-see" investigation. The drop in a working sleep mode design is minimal.

 

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Some words of caution about the AN8009. (So pretty much off topic).

I bought 2 of them as "extra" meters, for those times you need to do measurements with 4 or more DMM's at the same time...

The AN8009 delivers a lot of bang for those few bucks, but it has a few shortcomings.

This meter is pretty good at measuring small values (current, voltage, ohm)

It does indeed have only 2 shunts for measuring currents.

Both are fused with pretty crappy fuses ( D= 3.5 x 10mm)

They look like unobtanium, but D = 5 x 20 mm fuse holders are relatively easy to fit in the housing.

The "A" and "mA" bus has a piece of bridge wire and is not measurable with a normal DMM, Silk screen says: 10mOhm.

The "uA" input has a shunt resistor of 100Ohm and is fused at 200mA.

So it can pass a 100mA current in the "uA" setting, but it just can't measure it.

"Burden voltage" would be 100mA * 100 Ohm = 10V which is unacceptable and would probably overload & burn out the shunt before the fuse blows.

The bigges shortcoming of this meter is the lack of a real "mA" range.

It has a 9.999A range (Resolution 1mA) and a 999.9mA range ( Resolution 100uA)

For currents between 1mA and 100mA this meter has a very low resolution.

 

About the diode trick:

A lot of small power supplies have a series diode as a reverse voltage protection.

You could put the AN8009 in current measurement mode and short the diode through the shunt in the AN8009.

This should be a pretty decent measurement for currents < 1mA with no modification or extra external components.

 

-------------------------------------

I sort of like Dave's uCurrent, but will never buy one.

It is not much more than a (pretty nifty) opamp in a 100x configuration in a small box and with a few precision resistors.

It is too expensive for occasional use, and to limited for daily work.

For occasional use I would cobble something together on a breadboard or whatever.

For daily work I would prefer a power supply with built in accurate meters.

I would like one of those Keithley SMU's such as the 2400 but those are not really affordable :(

Think about USD 5000+

https://duckduckgo.com/html?q=keithley+2400

 

A power supply for 0 to 10V and 0 to 200mA and accurate measurements is not too difficult to design though.

It could also easily compensate for shunt and lead voltage drops, or even 4 wire feedback.

Dave Jones is currently developing a power supply with those sort of specs (Look at his video of custom LCD design)

It is a follow up of his uSupply which he never finished.

https://www.eevblog.com/projects/usupply/

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Thu. Aug 30, 2018 - 05:19 PM
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valusoft wrote:

Brian Fairchild wrote:

When buying a meter with a uA range you need to keep an eye on the 'burden voltage' spec. Or, in other words, the value of the shunt resistor used to measure the current. Some cheap meters can easily drop a few 100 millivolts which is not much good when your uC is running on 1.8V.

That is the whole (or nearly) basis of Dave's design. Don't introduce a burdensome (forgive me please) burden voltage into your measurement setup.

 

Yup, that's why I suggested the PAC1934 Eval Board. With 16b ADC and a maximum of 100mV,  that gives VSENSE LSB Step Size VSENSE_LSB — 1.5 — μV Unidirectional currents

 

If we scale the OPs 2mA to a 6mV burden, that's a 3 Ohm shunt, for 2mA full scale reading of 6m/1.5u = 4000 or 0.5uA LSB, The 16b ADC limit here, is hit at 33mA across that 3 ohm shunt.

 

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"Dare to be naïve." - Buckminster Fuller

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Who-me wrote:
With 16b ADC and ... If we scale the OPs 2mA to a 6mV burden, that's a 3 Ohm shunt, ...
A forthcoming energy meter apparently has a 14b ADC, a burden voltage of 25mV at 1A, and an impressive bandwidth.

The Embedded Muse 368 - Joulescope Review - An Energy-Measuring Instrument

by Jack Ganssle

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In June the Joulescope will be priced at $799. Kickstarter offerings are much less.

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Because engineering without numbers isn't engineering. It's art.

 

"Dare to be naïve." - Buckminster Fuller

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I do this regularly with one of Dave Jones current adaptors and they really are amazingly accurate and good value. A couple points however. If your on too low a range it’s hard to notice you’ve saturated it, and secondly you can replace those silly coin cell thing with three AA or AAA batteries to increase the range on each setting.

A second device I use a lot is the Mooshimeter, which is a stand-alone Bluetooth multimeter. The beauty of this is that you can record voltage and current simultaneously with a reasonably low current threshold.

Thirdly if you use an oscilloscope don’t forget that you’ll be grounding the negative terminal to the common sense point of your current amplifier - this can cause no end of weird effects including current flowing into or out off the scope ground back to your device under test.

M.

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

Last Edited: Tue. Feb 26, 2019 - 06:27 AM
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I am building a current measuring module right now. It is specially designed for time varying loads that are difficult to measure with a multimeter. Example is periodic writes to a memory card. It is built around a set of supercaps; you measure the change in voltage over some time interval to get the average current during that interval. Using a supercap maintains the low source impedance for the load, so that the load voltage does not vary much during peak loads. This is particularly important for loads containing switch-mode power converters.

 

I got the minimum 3 boards from the prototype house and enough parts to populate all. Guessing the price will be around 30USD. You can also order them as a shared design from OshPark. I will have a manual with complete schematic, bom, and use instructions. Each board has 4 1F (nominal) supercaps, a means to charge them, and a calibration resistor. You can switch in any of the 4 to optimize the discharge time for best resolution. There are binding posts for the charging side, the load side, and an additional pair for connecting a DVM. Minimum current is around 50uA (due to self discharge). I will have up to two that I'll sell for my cost, unassembled.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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If you are going low cost, check out Andreas Spiess's video: #245 Deep-Sleep Current: Which is better? µCurrent or CurrentRanger? (ESP32, ESP8266)

 

If you want something better, you can check out my Joulescope Kickstarter campaign as mentioned by gchapman!  VoltLog did a great teardown and review.

 

 

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Joulescope Precision Energy Analyzer Now Live on KickStarter | EEWeb Community

by Max Maxfield

February 19, 2019

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Matt [Liberty] is the founder of Jetperch, an engineering services company that tackles hardware and software development challenges across a wide range of industries, including consumer electronics, telecom, and industrial.

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"Dare to be naïve." - Buckminster Fuller