Luckfox Forums

Hello everyone,
I'm testing ADC readings for an external battery voltage.
I'm using a resistor voltage divider with 470kΩ on the top and 100kΩ on the bottom.

When the divider output is not connected to the SARADC_IN0 pin, the voltage is stable. However, when I connect it to SARADC_IN0, the output voltage drops noticeably.

Could you please advise on the input impedance of the ADC?
Do I need to use an op-amp buffer in this case?
Thank you

Hello, we have not actually used the method for measuring battery voltage in RV1106. And we do not provide technical support for hardware design-related issues. You can analyze the electrical properties related to ADC by visiting the https://files.luckfox.com/wiki/Luckfox- ... 231218.pdf page.

Hello Crocodile
When checking PDF schematic, we saw the SARADC0 connected to Boot button circuit.
This not good for ADC put with pull-up resistor to 1V8.
Really dont have option for isolation the circuit of Boot button on Luckfox Pico Ultra design.
Next, we checked the SARADC1, but saw it connected to net CDS+, but we dont have any same net connection.
I believe that you can help to confirm this, because your team designed this dev board.
Thanks.

The SARADC0 on the Luckfox Pico Ultra uses a pull-up resistor because, during the U-Boot stage, the system relies on the voltage level of this pin to determine whether to enter download mode. If the pin is left floating, it can lead to unstable system startup or failure to enter download mode.
This pin can be reconfigured via software. If your design is based on the Core1106, you can choose to use other GPIOs instead. However, on the Luckfox Pico Ultra, using this pin for battery voltage detection may produce inaccurate results due to the presence of the pull-up resistor.
In the schematic, CDS+ is a no-connect (NC) net, so SARADC1 is directly connected to the header pins.

I recommend creating a topic that clearly specifies the model in use, and by default, assumes the peripheral hardware design is based on the Core1106.