How to change current scale on display?

[James Cameron]

G'day,

Am sourcing 5V on channel B to drive an Arduino, which flashes an LED,
which is also being measured on channel A.

I wish to get a better idea of the changes in current, but the detail
is hard to see.

How do I configure channel B to display more vertical detail?

(Workaround: export, and read the numbers).

--
James Cameron
http://quozl.linux.org.au/

[Ian Daniher]

Workaround is to use the #enableigain flag, like apps.nonolithlabs.com/edge/pixelpulse#enableigain. Note that there's a small DC offset with common mode voltages greater than 2v, but this shouldn't negatively impact the AC measurements.

Best!

--

Ian

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[Dan Steingart]

Hi Ian:

Does this actually improve the the sensor resolution or just the reported resolution?  

Thanks,

Dan

[Ian Daniher]

This enables the analog programmable gain amplifier in our ADC, improving the sensor resolution, but at higher gain levels, the 2v DC offset dominates measurements.

[Dan Steingart]

Just to be clear, this is a constant correction factor offset, correct?

Thanks in advance.

[Ian Daniher]

The dynamics of the error are adequately captured by this plot of a voltage sweep of an unloaded channel with current gain at max:

This error occurs when the analog input frontend of the MAX9919F current sense amplifier used on CEEs V1.0 and V1.1 undergoes a voltage-dependent transistor transition. See https://github.com/nonolith/CEE/issues/25 for more discussion.

Few workarounds:

Use a channel set to 0v as a low side current sensor. This is approach has limitations, but works sufficiently well when you're attempting to interact with a two terminal device that has no connections to external / earth ground.

Ask me about V2 and V3. I use V2rc1(https://github.com/nonolith/CEE/tree/v2rc1/eagle) on the daily. It uses an INA213 current sense amplifier which doesn't suffer from the aforementioned transition glitch, but limits the effective current control bandwidth to not better than 5KHz. V3 is a complete redesign I've been working on in collaboration with some folks at Analog Devices.

Best!

--

Ian

[Dan Steingart]

Any dates on V3?  Would you ship some units with V2rc1 ( :) )?

[Ian Daniher]

No dates on V3 yet. Email te...@nonolithlabs.com with more info about your need for V2rc1 & we can likely work something out in the immediate future.