Measuring low current

[Moshe Livne]

I am trying to build some low powered sensors and following some threads here but it seems that i lack any instrument that can measure milliamps. I have very little electronics background and only own a half decent multimeter. Any recommendations? tricks? will KEW MATE 2000 work well? its the only thing made by a respectable firm that i found that can measure current with clamp for under 200$ (although i couldn't figure how low it can get). Anyone has good experience with the chinese clamps meters on ali? I had some disappointments lately so twice shy.

[tbowmo]

@Moshe-Livne

Have you checked out uCurrent from eevblog?
http://www.eevblog.com/projects/ucurrent/

It's used by a number of persons here on the forum (myself included)

[Moshe Livne]

@tbowmo Thanks. As i said - very little background so didn't even know about the option. seems very accurate and cheap! I wish someone knowledgeable will write a complete tutorial about increasing battery life. currently there are some very good threads but they mention for example removing the LED and voltage regulator without much details and I am afraid to hurt my 2.5$ nano....

[Moshe Livne]

Just to anyone who happend to find this thread while looking for ways to conserve battery power, this is a very good place to start http://www.mysensors.org/build/battery

not everything there is 100% clear but I guess its manageable.

[scalz]

@Moshe-Livne : if you want, this link is very interesting https://hallard.me/category/ulpnode/
Sure he is not using an arduino mini, but his board consumes only 400nA-800nA in sleep mode. And he is trying to make it mysensors compatible!

[AWI]

@Moshe-Livne Even more practical information by @EasyIoT : Low Power

[Moshe Livne]

@scalz this is very similar to sensebender, right? Anyway, the price per node is too high for the amount of nodes I need (if it is even in production!)

[Moshe Livne]

@AWI How can he directly measure such small currents? I thought that the multimeter itself when used in serial will create too much disturbance, thats why I was planning on getting the ucurrent.
I know very little about these things, just repeating what I read/heard.

[AWI]

@Moshe-Livne Measuring low currents is a kind of science. You can choose to be more practical and take the risk of non-accuracy and obvious mistakes. When measuring current with a multimeter you basicaly put a resistor in series with the load. The voltage drop (or Burden Voltage) over this resistor (called shunt) influences your measurement. The quality (sensitivity) of the used (multi)meter determines what the error is.

The Ucurrent is in fact a very very sensitive volt meter (green) over a low value shunt resistor (10 k ohm, 10 ohm or 10 milliohm)

In practice: most budget multimeters can be used in the milli-amp range for determining the ballpark current/power consumption of our MySensor Arduino's. Typically in the 0.1mA (100nA) to 30mA range. There is a tendency in part of this community to reduce power consumption to a kind of sub-zero level. To put it into perspective: with a current consumption of 100nA (which can be measured in-accurately with a budget multimeter) 2AA Alkaline cells (2000mAh) will last for more than 2 Years. The real consumption comes from the active mode of the Arduino, powered Sensors and the radio in relation to sleep time.

I own a ucurrent (of course ) and had to discover the hard way that most power consumption comes from stupid design errors, like:

• Voltage dividers
• High dissipation sensors
• (internal) pull-up resistors with a constant load
• (feel free to add to the list)
  All of which can be easily found with a budget meter.... but it is our hobby so we need stuff like ucurrent/ 3D printers / oscilloscopes.

[Moshe Livne]

@AWI totally understandable! I am a bit relived to hear that actually. I own a reasonable (I think) multimeter - not the cheapest from aliexpress... it is reasonably ok but everyone is so hushhush about the accuracy. I even ended up asking some multimeters companies what is the *&%&% accuracy and stop giving me all sorts of equations to solve!!!
It reminds me of my other hobby, woodworking. You can do almost anything to a really good degree of finish with couple of hundreds $ of equipment BUT (and its a big capital BUT):

1. You need to know what you are doing
2. You need to carefully select this equipment and usually you gain the insight only after spending couple of K$ on useless hyped things.
3. You need to have the confidence required
4. it does take more time and can end up less accurate.

Thanks for this... now I can use my multimeter with more confidence