ADS1115 negative voltages

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ajsweet2022
 
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Joined: Sat Sep 24, 2022 11:15 pm

ADS1115 negative voltages

Post by ajsweet2022 »

Im trying to use an esp32 and ADS1115 to measure 2 x 15 volt batteries wired in series (-15VDC - 0 - +15VDC )

If possible, I want to measure each battery (independely) with one ADS1115

At the moment I'm using a simple 2 resistor voltage divider , to measure one of the batteries, so 1 battery (15VDC) is represented at the ADS1115 input A0 , at 6 VDC.

However, I cant figure out how to measure the other battery with the same ADS1115 ....do I need another voltage divider that changes -15VDC to -0.3VDC (max negative input for the ADS1115) ?

Or something else?

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adafruit_support_bill
 
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Re: ADS1115 negative voltages

Post by adafruit_support_bill »

The ADS1115 cannot measure voltages less than GND. All input voltages to the ASD1115 must be between GND and VDD. https://www.ti.com/lit/ds/symlink/ads1115.pdf
(The "Absolute Maximum" rating is -0.3v to VDD+0.3v, but as the datasheet says, these are 'stress ratings' only:
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability
To measure negative voltages, you need to use the differential mode measurement. This takes two inputs (both between 0v and VDD) and measures the difference between them.

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