Author Topic: Battery powered 4-20mA/0-10V analog input module for low power battery module  (Read 973 times)

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Offline virtappTopic starter

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Hi guys,

I've actually done some experiments for my low power battery-operated arduino pro mini sensorboard following this guide (https://learn.sparkfun.com/tutorials/reducing-arduino-power-consumption/all) i've reached 5uA of current draw from arduino in deep sleep.

Now, i need to design something that can allow me to acquire two type of signals: 4-20mA and 0/10V, i know that this can be done in a bunch of ways, but i need to use low-power designs in order to keep my sensor run on battery for at least 2 year.

I'm planning to use standard AA batteries like these old-fashioned Duracell Plus Power https://docs.rs-online.com/1623/A700000007325672.pdf, they are claims to be able to deliver 3Ah per single cell and i want to use two of them in series, so i can reach 3V.

My maximum target consumption during sleep can be around 20-25uA during deep sleep.

My thoughts drive me to this schematic: using a low power NCS20062DR2G (https://www.onsemi.com/pdf/datasheet/ncs2006-d.pdf) in this configuration i can read 4-20mA, 0-10V...and in addition a dry contact from external sensors/systems.



In order to put everything on battery and keep it "zero" on consumption during sleep, i'm thinking to attach the VCC pins to a Arduino digital pin output and then do a digital write high (putting it to 3V).

Anyway, i have some doubts about this design:

  • How it works when the battery discharges...say at 2.3V?
  • It can be a good solution for this specific purpose?

I'm completely opened to alternative solutions, please note that this is only my initial idea...and i'm not sure about that.

About the given schematic, this was seen on Iono Arduino board, you can find more informations here: https://www.sferalabs.cc/files/ionoard/doc/ionoard-user-guide.pdf (at page 8).

And for completeness, here it's the complete schematic of the Iono Arduino Board: https://www.sferalabs.cc/files/ionoard/doc/ionoard-sch.pdf
 

Offline esepecesito

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I would not use any op-amp. just couple of resistors and direct to A/D input.
Good question about the voltage: the "Ah" rating of the batteries is total capacity, including the discharge well below the nominal 3V. Typically you should have a dc/dc converter which warranties the 3V.
 

Offline Benta

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Are your external sensors self-powered?
 

Offline virtappTopic starter

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Yes, the sensors are already powered up with typical +24VDC DIN power supply.

And yes, i've changed my initial approach and i've chosen to keep it simple: i'm planning to use a simple ADS1115 in this configuration:



About the batteries i'm planning to use, i'm considering these Energizer Lithium Iron Disulfide AA Batteries 1.5V https://uk.rs-online.com/web/p/aa-batteries/1966692/ with this typical discharge curve:




You think that will be a good choice?

Thanks.
« Last Edit: July 12, 2021, 10:15:58 am by virtapp »
 


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