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[SAADC] how to measure battery with more precision digits

[CONDITION] 1. R1 = 1.5M, R2 = 430K 2. GAIN = 1/2 3. RESOLUTION = 10bits 4. Single End

[ISSUE DESCRIPTION] 1. If voltage is changed by 0.1V step (4.1V -> 4.0V), the outputs from ADC is ok to distinguish. 2. However, if voltage is changed by 0.01V step (e.g. 4.12V -> 4.11V), the outputs from ADC is overlapped for some range, resulting in ambiguous readings to tell 4.12V from 4.11V, or vise versa.

[QUESTION] How to make SAADC work to get battery voltage with more precision digits: e.g. 4.1V, 4.11V, 4.111V, ....?

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  • nRF52832 has a 12 bit ADC, and the spec says

    "14-bit resolution with oversampling"

    This is 2 bits better than the nRF51's ADC

    I'm not sure however I fully understand your problem.

    If your resistor divider is 1500k and 430k , you can measure up to voltages of 4.246V as that divides to 3.3V at the ADC

    For for a 10 bit ADC, thats 1024 steps so 4.246 / 1024 = 0.004V resolution. Which is better than you now say you require.

    However....

    I think you do not fully understand the operation of an ADC. See devzone.nordicsemi.com/.../

    So you need you either need to use much lower value resistors (which may be impractical as it would flatten the battery). Or you need to implement a circuit described here

    devzone.nordicsemi.com/.../

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