Questions about nRF52840 ADC

[ericwelch1]

We are using nRF Connect SDK 1.8.0 with Seggar Embedded and I have a number of questions.

1. What is the best Nordic example for ADC on this platform?

2. While we have been able to use add_read(), the call add_read_async() doesn't appear to exist in the 1.8.0 SDK.  Why?

3. We have experimented with the ADC reference "Internal" and the accessor suggests that this is 600 mV.  However, using ADC_REF_VDD_1 or ADC_REF_VDD_1_2 produce errors when adc_read() is called.  Why is this?

prj.conf includes

# ADC
CONFIG_ADC=y
CONFIG_ADC_NRFX_SAADC=y

zephyr.dts includes:

adc: adc@40007000 {
compatible = "nordic,nrf-saadc";
reg = < 0x40007000 0x1000 >;
interrupts = < 0x7 0x1 >;
status = "okay";
label = "ADC_0";
#io-channel-cells = < 0x1 >;
};

4. we are using pins AIN6 and AIN7.  We always get data, but it is apparently not always  related to the voltage on the input pin.

Any input or suggestion would be welcome.

[Jared]

Hi,

1. What is the best Nordic example for ADC on this platform?

I would suggest this one. 

2. While we have been able to use add_read(), the call add_read_async() doesn't appear to exist in the 1.8.0 SDK.  Why?

Strange, both should be available in NCS v.1.8.0. Are you getting any specific errors when you try to use it?

3. We have experimented with the ADC reference "Internal" and the accessor suggests that this is 600 mV.  However, using ADC_REF_VDD_1 or ADC_REF_VDD_1_2 produce errors when adc_read() is called.  Why is this?

prj.conf includes

# ADC
CONFIG_ADC=y
CONFIG_ADC_NRFX_SAADC=y

zephyr.dts includes:

adc: adc@40007000 {
compatible = "nordic,nrf-saadc";
reg = < 0x40007000 0x1000 >;
interrupts = < 0x7 0x1 >;
status = "okay";
label = "ADC_0";
#io-channel-cells = < 0x1 >;
};

Exactly what errors is returned? 

4. we are using pins AIN6 and AIN7.  We always get data, but it is apparently not always  related to the voltage on the input pin.

Are you using a custom board or the PCA10056 development kit?

regards

Jared n

[ericwelch1]

When using an apparently unsupported Reference, the error is -21 (which I understand is EINVALID, meaning that the setup isn't supported)

We are using a custom board, but the clock and power duplicate the NRF9160_nRF52840 as closely as possible.  We have a custom AFE connected to AIN6 and AIN7

[Jared]

Hi there,

Could you share a minimal example that reproduces the issue on a development kit?

regards

Jared