Author Topic: uCurrent Gold and a lot of noise on oscilloscope  (Read 10925 times)

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Offline Gyro

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Re: uCurrent Gold and a lot of noise on oscilloscope
« Reply #25 on: March 05, 2016, 04:32:42 pm »
Oh i see (and no need to get on your high and mighty) the problem then is that you have an ambiguos reading. The idea is that mV = nA, uA and mA, if you do each decade it will be so confusing it will make life harder. A multimeter reads in mV or V, to have 100mV per 1nA, 10nA, 100nA, 1uA, 10uA, 100uA, 1mA, 10mA, 100mA will be very confusing if your trying to use all ranges. Of course a more complex product could do as you want but it would be more expensive as it would need it's own display and a more complicated case.

Live and let live then :).

 I thought I was being fairly clear, the mV I was talking about in all cases was the voltage drop across the shunt resistor for a given current, sorry if it was confusing.

Sure, I appreciate that one of the aims of the uCurrent was to be as cheap possible to manufacture by putting everything on the PCB, unfortunately that inevitably leads to compromises like multi-way switch availability, which limits number of shunts, which....  It's what you need to do to meet the selling price and of course a weak point in comparison with what can be made one-off - as always with commercial products.

Yes, you can certainly use external shunts across the terminals, and probably a good idea to do it on the 'bottom ends' of the uA and mA ranges to trade a slightly higher voltage burden for less noise. Unfortunately not possible on the nA range as the 10k is already there - maybe an option to switch out all internal shunts would be useful addition, leaving the actual uCurrent as a low offset, high impedance amplifier (there's always an option for the user to remove the 10k of course).
Chris

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Offline Simon

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Re: uCurrent Gold and a lot of noise on oscilloscope
« Reply #26 on: March 05, 2016, 04:44:19 pm »
Yes that's what I meant. Remove the 10k resistor and you have the flexibility to do what you like but obviously it's not a self-contained unit any more. The other thing is that you can use an oscilloscope to view the output so 9 different ranges might cause confusion here as well although I suppose if you played with the divine factor of the oscilloscope probe setting you could get it right but again it takes a lot of messing about to do that and you can't just switch seamlessly between ranges and have an easy read out.
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Offline deephaven

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Re: uCurrent Gold and a lot of noise on oscilloscope
« Reply #27 on: March 05, 2016, 05:01:08 pm »
When I do such measurements (with or without a uCurrent) I feed the output into the scope via a simple RC filter straight into it's BNC, no probe. Depending on how much detail you need to see in the current ripple, you can adjust the values in the RC filter accordingly. Typically I use a 10K series resistor followed by a 100n capacitor to ground. No noise then.
 

Online borjam

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Re: uCurrent Gold and a lot of noise on oscilloscope
« Reply #28 on: March 16, 2016, 11:49:07 am »
How else can you measure the consumption of tiny microcontrollers without spending a fortune?

Not difficult, you just need a series resistor and a bit of voltage gain. You can do it very cheaply.
Good luck! what do you think the uCurrent is ? it is litterally that, a resistor and a 100x amp. The problem with dealing with such low voltages is offset voltage on the amp so the uCurrent was designed to resolve that with a good amplifier.

Exactly. So much stuff can be homebrew, yet I need to get some measurements, and this little box solves my problem while I focus on the rest of the project.

 


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