[volt-nuts] Cheap Oscilloscope measurement of small current?

[Peter Loron]

If you wouldn't mind, I'd appreciate a more detailed explanation of the setup you're using. A stab in the dark gives me this schematic:

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On Nov 5, 2010, at 7:08, Oz-in-DFW <lists at ozindfw.net> wrote:

> I'm doing quite a bit of this and like most things, the answer is "it
> depends. " 
> 
> What I'm doing right now is using a resistor in series with the _input_
> of a low leakage micropower Low DropOut (LDO) regulator because this (15
> uA) circuit will run off of a regulated supply.  The LDO has a steady
> state consumption of a few microamps and that is largely a function of
> input voltage and operating temperature at the low operating currents
> I'm dealing with.  My workshop temperature is constant enough.  This
> works well below a uA.  I just use my plain old Tek scope with two
> channels in differential mode.  If I neede teh extra channel I'd brew a
> diff amp or use something like this:
> 
> http://datasheets.maxim-ic.com/en/ds/MAX9938.pdf
> 
> I believe you have a much more complex problem.  You will be operating
> from battery or solar supplies that likely have a defined voltage and
> internal resistance over time.  This can have a profound impact on
> operating time, particularly if subtle considerations are as significant
> as you imply they are.  You'll either need to take a lot of measurements
> and model the supply carefully, or you'll need a good simulator of the
> supply. 
> 
> On 11/4/2010 6:07 PM, Peter Loron wrote:
>> Hello, all. I'm working (very slowly, but working) on some designs that
>> will be battery (and possibly solar) powered sensors with a wireless
>> data backhaul (likely 433 or 915MHz).
>> 
>> As part of my never ending quest for more tools, I'm starting to educate
>> myself on what I may need to get measurements on current usage over time
>> for these devices. I want to be able to quantify power usage while it is
>> asleep, sensing, sending data, etc..."does changing this code shorten
>> the radio on time?"
>> 
>> I'm sure Agilent would be happy to sell me a fancy oscilloscope current
>> probe for more than my condo cost, but I'm looking for something more
>> cost effective.
>> 
>> Suggestions from the hive mind?
>> 
>> Thanks.
>> 
>> -Pete
> -- 
> mailto:oz at ozindfw.net    
> Oz
> POB 93167 
> Southlake, TX 76092 (Near DFW Airport) 
> 
> 
> 
> 
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