F429 disco ADC outliers

[ChrisMicro]

The ADC functions randomly return 0 for several seconds.

[danieleff]

Can you put here a short test code for it?

[ChrisMicro]

It's a long time. I think it was this code:
`

/************************************************************************

STM32F546 Discovery simple oscilloscope example

The oscilloscope has a auto trigger function to achieve a stable
visual impression when a repeating signal like a sine wave is applied.

May 2017, ChrisMicro

************************************************************************/

#include "TFT_F429_Discovery.h"

TFT_F429_Discovery tft;

#define HORIZONTAL_RESOLUTION 240
#define VERTICAL_RESOLUTION 200
#define POSITION_OFFSET_Y 20
#define SIGNAL_LENGTH HORIZONTAL_RESOLUTION

uint16_t oldSignal[SIGNAL_LENGTH];
uint16_t adcBuffer[SIGNAL_LENGTH];

#define SAMPLING_TIME_US 20
#define ANALOG_SIGNAL_INPUT PC12

void setup()
{
tft.begin();
tft.fillScreen( LTDC_BLACK );
tft.fillRect(10, 1, 150, 160, LTDC_BLACK);
//tft.setRotation(1); // horitzontal wide screen
tft.setCursor(0, 0);
tft.setTextColor(LTDC_GREEN); //tft.setTextSize(3);
tft.setTextSize(2);

tft.println("analog input PC12");
tft.print("sampling frequency: "); tft.print(1000000 / SAMPLING_TIME_US); tft.println(" Hz");

// configure the ADC for 12 Bits
analogReadResolution(12);
}

void waitForAutoTrigger()
{

uint32_t triggerLevel = 512;
uint32_t hysteresis = 10;
uint32_t timeOut_ms = 100;

uint32_t timeOutLimit = millis() + timeOut_ms;
uint32_t timeOutFlag = false;

uint32_t adcValue = 0;

adcValue = analogRead( ANALOG_SIGNAL_INPUT );

// wait for low level
while ( ( adcValue > triggerLevel - hysteresis ) && !timeOutFlag )
{
adcValue = analogRead( ANALOG_SIGNAL_INPUT );

if ( millis() > timeOutLimit ) timeOutFlag = 1 ;

}

if ( !timeOutFlag )
{
// wait for high level
while ( ( adcValue < triggerLevel + hysteresis ) && ( millis() < timeOutLimit ) )
{
adcValue = analogRead(ANALOG_SIGNAL_INPUT);
}
}

}

void showSignal()
{
int n;

int oldx;
int oldy;
int y;

for (n = 1; n < SIGNAL_LENGTH; n++)
{
y = VERTICAL_RESOLUTION - ( adcBuffer[n] * VERTICAL_RESOLUTION / 1024 ) + POSITION_OFFSET_Y;

if (n == 1)
{
  oldx = n;
  oldy = y;
}

if (n < SIGNAL_LENGTH - 1)
{
  // delete old line element
  tft.drawLine(n - 1 , oldSignal[n - 1], n, oldSignal[n], LTDC_BLACK );

  // draw new line element
  tft.drawLine(oldx,               oldy, n,            y, LTDC_GREEN );
}

oldSignal[n - 1] = oldy;
oldx = n;
oldy = y;

}
}

void loop(void)
{
int n;
uint32_t nextTime = 0;

//waitForAutoTrigger();

// record signal
for (n = 1; n < SIGNAL_LENGTH; n++)
{
adcBuffer[n] = analogRead( ANALOG_SIGNAL_INPUT );
//adcBuffer[n] =random(0,200);
// wait for next sample
while (micros() < nextTime);
nextTime = micros() + SAMPLING_TIME_US;
}

showSignal();
delay(100);
}
`