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How to sense a 8Hz signal from the ADC3 pin(shared with mic) of SensorTile (STM32L476xx)?

Question asked by Abhilash Iyer on Aug 20, 2017

I recently purchased a SensorTile  which has a STM32L476(JGY6) microcontroller inside it. It looks like that there are 3 ADC pins coming out of the board - ADC1, ADC2, and ADC3.  ADC1 & ADC2 are shared with I2C3 on which there is a temperature sensor. So, I am choosing the ADC3 channel to read my analog inputs coming at 8Hz. 


I have two questions: 
1. The ADC3 channel comes from the pad 3 (MIC_CLK) of MIC. Will this affect my sensitivity?  


2. This one is a basic one - Is there a C code example on how to listen to ADC channels from STM32L476? If the functions of the ADC getdata() is implemented, Can someone tell me where exactly is it? How to use it? 


I saw a stm32l476xx_nucleo.c  example in which they interface the joystick at the ADC 1 channel. But the code has two variables which I am not sure what they are: 

static ADC_HandleTypeDef hnucleo_Adc;
static ADC_ChannelConfTypeDef hnucleo_AdcChannelConfig; 


Here is the relevant parts of the code: 
* @brief ADC Interface pins
* used to detect motion of Joystick available on Adafruit 1.8" TFT shield
#define NUCLEO_ADCx ADC1

#define NUCLEO_ADCx_GPIO_  PIN       GPIO_PIN_0


/ ADC Private functions
static HAL_StatusTypeDef ADCx_Init(void);
static void ADCx_MspInit(ADC_HandleTypeDef *hadc);


Will I have to implement the ADCx_MSPInit() and ADC_Init()? And also where can I find the definitions of functions & variables of ADC in the following code? 


hnucleo_AdcChannelConfig.Channel = ADC_CHANNEL_15;                                 // What channel is 15? There are only 3 available channels right?
hnucleo_AdcChannelConfig.SamplingTime = ADC_SAMPLETIME_24CYCLES_5; // Definition?
hnucleo_AdcChannelConfig.Rank = 1;
hnucleo_AdcChannelConfig.SingleDiff = ADC_SINGLE_ENDED;
hnucleo_AdcChannelConfig.OffsetNumber = ADC_OFFSET_NONE;


It would be really great if you could provide some help.