ADC input status during low power mode?

[DonpK]

I am using a voltage divider from Vcc to measure the battery voltage supplying an Arduino Uno-type device. The divider is used to reduced the ca. 5 volt Vcc value so the internal 1.1 volt reference can be used. This divided voltage is connected to an analog input.

Using the LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF) function, the device current is slightly higher during the sleep mode with the analog input left connected to the voltage divider. The additional current with the ADC connected depends on the size of the resistors in the divider. It can range from 1µA with high-value resistors to 7 or 8 µAs with lower value resistors.

What is the actual status of the analog inputs during the sleep mode? It would appear that it is not entirely an open circuit, but has some high impedance drawing current through the resistor divider.

[LIM PHANG MOH]

Hi,
I think you might have already found your answer in the forum.
But, as I have been using the same resistor divider and a capacitor to measure the battery voltage using the internal 1.1V reference all this while but it is always on pin ADC6 or ADC7. So, if you look at section 23.9.5 of the datasheet (register DIDR0), that might be answer. I have yet to dig the Arduino core on whether they does this when using the pin as an analog pin. Chances is they don’t as this is granular detail in power optimization but I could be wrong.

[DonpK]

Thanks for your answer. “section 23.9.5 of the datasheet (register DIDR0”. What datasheet are you referring to? Do you have a link or more details?

[LIM PHANG MOH]

I’m referring to the ATMega328P datasheet. I think I was referring to the older datasheet. On the latest datasheet it is on section 28.9.8 at page 326.

[DonpK]

Thanks, I found the section you were talking about. As author of the Low Power Library, I think you are perhaps the best person to answer your own question.

The low power consumption rates I am getting seem reasonable. I’m sure you’ve seen the other articles on the internet using your library. My results seem in line with them.

[CoraDias]

Hi…i am a new user here. I was also working for same kind of project and have been using the same resistor divider and a capacitor to measure the battery voltage using the internal 1.1V reference all this while but it is always on pin ADC6 or ADC7. So, if you look at section 23.9.5 of the datasheet , that might be answer. I have yet to dig the Arduino core on whether they does this when using the pin as an analog pin.

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