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I am working on a battery powered project. With a multimeter I've been measuring current on the "positive" side of a module and observe 5μA.

However I thought to measure the "negative" side and was surprised to observe a value of 4.6mA, which is a wildly larger value from 5μA.

In terms of calculating battery life, how do I consider -4.6mA versus +5μA? Am I measuring what I think I am measuring, that being current consumption?

I've read over Q/A's such as How to calculate battery life and How do I calculate battery life for my devices? but these don't provide an answer. I'm totally new to all things electrical. I've searched for answers to this question but I know so very little likely I don't know the correct search terms.

Edit:

@AliChen's first comment prompted me to disconnect the TX/RX lines and having done so, the current measurements are congruent. Exactly determining the why, of course, is another matter for me to pursue.

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RamblinRose
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  • Can you describe load and layout? You may need a bypass cap to shunt your probe inductance if the load is pulsed. – Tony Stewart EE75 Jan 18 '18 at 15:26
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    Please can you post a diagram of what you have, with detail rather than a box labelled 'load' :-) The more you put in, the better the quality of the answers you'll attract. – TonyM Jan 18 '18 at 15:46
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    Also just to add, it seems like you're saying that you have 5uA coming out of the positive terminal, and 4.6ma going into the negative terminal. This is fundamentally impossible, indicating that there is a problem with your measurement setup. We might be able to help you fix that problem if you post a schematic. – BeB00 Jan 18 '18 at 16:12
  • What a tough crowd! ;) I hope this is what you're asking for I kid not when saying I am new to electronics. I didn't know how to use a multimeter a 6 weeks ago (possibly still don't?). To measure current I am running either the +/- leads from the 3V3 or GND lines through the multimeter. It's quite possible I am doing everything wrong! – RamblinRose Jan 18 '18 at 16:37
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    To be clear by +/- leads I meant TEMP μA/mA and COM on the multimeter. – RamblinRose Jan 18 '18 at 16:51
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    "What a tough crowd!" - We are only trying to help. An experienced EE can tell you more from glancing at a schematic than asking dozens of questions about your problem. – Bruce Abbott Jan 18 '18 at 17:42
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    To calculate battery life you need to know how much current is being drawn from it. But you don't show a battery in your schematic so we can only presume it is powering the Arduino through Vin and GND. If so then you should measure current there, not at the BLE module. – Bruce Abbott Jan 18 '18 at 17:57
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    Ok. Please provide TWO schematics, where the battery is, and where did you take your TWO measurements. What is "BLE", and where it is connected to? I suspect that some Rx/Tx lines are powered as well, and contribute to the return ground current. – Ale..chenski Jan 18 '18 at 18:09
  • @BruceAbbott indeed the diagram does not show a battery. I presume for observing current the source of the current (3.3V from an UNO or from a battery) is not germane. Clearly it will affect battery lifetime calculations, but for now I am simply confused about the values I observe between the positive an negative. – RamblinRose Jan 18 '18 at 18:11
  • @AliChen you nailed it, when removing the TX/RX lines the 3V3 and GND currents equate. Currently I do not understand why, of course. – RamblinRose Jan 18 '18 at 18:15
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    To understand why, you need to show where the TX/RX are connected to. They likely have resistor pull-up (to +3.3 V) on the other side of connection. That's why complete schematics (including battery, connection source, at which point did you insert your DMM, etc.) is needed to diagnose your confusion. – Ale..chenski Jan 18 '18 at 18:19
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    @BruceAbbott "what a tough crowd" was a purely mirthful comment, hence the wink. Having been savaged on stackoverflow a few times I can say this board is a good bit more tolerant of newbies. – RamblinRose Jan 18 '18 at 18:19
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    @AliChen that's what I suspected too. Make your comment into an answer and get some points! – Bruce Abbott Jan 18 '18 at 19:22
  • "What a tough crowd!" - well, what an impossible question :-) Unfortunately, you've drawn a box marked 'load', as I'd said not to do because we can't do anything with it besides guesses. Can't see a battery there. It's up to you to detail it if you want a decent answer, I'm afraid... – TonyM Jan 19 '18 at 08:53
  • Long comment stream and no answers. Already flagged as too broad... –  Jan 20 '18 at 01:20

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