Author Topic: Current Ranger from LowPowerLab  (Read 361 times)

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Offline kgmuzungu

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Current Ranger from LowPowerLab
« on: February 27, 2020, 07:03:24 pm »
Bad experience with the Current Ranger from LowPowerLab. The Current Ranger is a copy of the uCurrent with some added features to it. I thought it would be open source but it is not. Felix, the guy who designed it and is moderating the forum, deletes forum entries explaining his product works or indicating parts he used but not mentioned in the schematic. Yes the schematic is published, asking myself, why then? He thinks it is his IP  |O. I would say Dave did the major work and deserves all credits. So my advice, dont buy it!

Initially he used the same config as Dave, two MAX4239 amps after each other (SMD mark ABAA), then in later versions he swapped the second op amp with the AD8628 (SMD mark A0L, you might read it also as AOL) which is a 5pin SOT23 package. I posted this on his forum. The post was deleted the next day with a comment asking why I am trying to reveal his secrets  :-DD.

And for anyone interested what GND-ISO is for and how the CurrentRanger bias-mode works (guess what, this post was deleted as well):
The reason that there is a GND and a GND-ISO in the schematic is that GND-ISO is the output of the DAC of the microprocessor and GND is the battery ground (min) to use the CurrentRanger in normal- or bias-mode.

Taking a non-inverting op amp voltage amplifier configuration and you put the feedback resistor not on ground but on an arbitrary voltage level (here GND-ISO) e.g. to bat/2 volt then the output of the op amp relative to the battery goes also to bat/2 V if there is no diff voltage present at the inputs. You can show that if you analyze the circuit on paper or you try it out or simulate it. With the CR you measure then the output voltage between the op amp output and GND-ISO, which is in bias-mode bat/2 or to whatever voltage you set the DAC output. In bias-mode if there is no input voltage then the output is zero because the op amp output and GND-ISO are on the same level. The output can go higher then bat/2 then you get a positive output voltage or lower then the output appears negative. That's how the bias-mode works.

Note: in the source code the voltage for GND-ISO is set with the variable "offset".

Note: If you have a noise signal then in bias-mode the positive and negative parts are amplified and might average out measured with a multimeter. In normal mode you might only amplify the positive part and create an DC error.

Conclusion: go for the uCurrent or take a transimpedance amp for ultra-low currents ... or something else.
 
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Re: Current Ranger from LowPowerLab
« Reply #1 on: July 28, 2020, 09:04:32 am »
Bad experience with the Current Ranger from LowPowerLab. The Current Ranger is a copy of the uCurrent with some added features to it. I thought it would be open source but it is not. Felix, the guy who designed it and is moderating the forum, deletes forum entries explaining his product works or indicating parts he used but not mentioned in the schematic. Yes the schematic is published, asking myself, why then? He thinks it is his IP  |O. I would say Dave did the major work and deserves all credits. So my advice, dont buy it!

Yes, the design does not seem to have properly followed the license. I released it under CC-BY-SA, that means "Sharealike", so his project should be released under the same license.
https://creativecommons.org/licenses/by-sa/2.0/au/

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