[MAGEEC] Accuracy of the power measurement shield

Jeremy Bennett jeremy.bennett at embecosm.com
Fri Mar 9 14:24:03 GMT 2018

Hash: SHA1

Hi Mark,

You'll see I have updated the Wiki in line with my email. Looks like
the ADCs are actually 12-bit.

Best wishes,


On 06/03/18 16:48, Jeremy Bennett wrote:
> On 06/03/18 16:26, Mark Kettner wrote:
>> Hello everyone,
>> could someone please tell me the accuracy of the measurement 
>> shield. How can I assume really low power (milli or micro) are 
>> still valid measurements and not just noise? Or is this purely 
>> affected by the selected resistor?
> Hi Mark,
> Good to hear from you. James Pallister and Simon Hollis reckoned
> the measurement is accurate to 1%.
> I'm out of the office at the moment, so don't have a board to look
> at. - From memory it uses a 10 bit ADC. To measure the current, the
> inserted resistor aims to create a maximum 50mV drop. The largest
> resistor on the board is 5R, which would therefore be for a peak
> current of 10mA. There is an option to insert a larger resistor if
> you wish. Voltage range is fixed I think at 0-6V.
> The circuit was designed to sample at up to 2MHz on each sample
> point, although at that frequency I would expect inductive and
> capacitive affects to impact on the accuracy. The standard tool is
> written in Python and in my experience struggles to sample at much
> more than 10kHz. However the design is fully open, so there is no
> problem with modifying the tool and/or the firmware to sample at
> these higher rates. You can find the software on GitHub.
>> Unfortunately I couldn't find anything about that in the wiki.
> Since the MAGEEC work finished some time ago, I've been less
> proactive in updating the wiki. However I'm happy to add some notes
> about this. I'll check the facts against the board when I get
> back.
> Best wishes,
> Jeremy
>> -- Mit freundlichen Gruessen / Best Regards
>> Mark Kettner _______________________________________________
>> mageec mailing list mageec at mageec.org 
>> http://mageec.org/cgi-bin/mailman/listinfo/mageec

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