Microcontroller returning from stand-by wont take sensor readings

Projects Programming
1

Hello everyone,

I am currently using a Seeeduino Xiao (ATSAMD21G18A) in a project. The project involves taking a temperature and ambient light measurement (I2C) every 10 minutes. The MCU should be in sleep mode otherwise. The LowPower.attachInterruptWakeup() from the Arduino low power library is not supported by the Xiao. I found this sleep and wakeup with RTC and tried to implement it. When the MCU starts the first measurements are taken but once it enters standby and wakes up, no measurements show up in the serial monitor again. However, the code in the while loop does execute as the blink sketch works. The sensors communicate perfectly without the stand-by mode. Here is the code:


#include "RTC_SAMD21.h" //install seeed_arduino_RTC : https://github.com/Seeed-Studio/Seeed_Arduino_RTC
#include "DateTime.h"
#include <EnergySaving.h>

#include<Wire.h> //include library
#define Address_GY49 0x4A // GY-49 I2C Address is 0x4A(74)

#include <Adafruit_TMP006.h>

Adafruit_TMP006 tmp006 (temperature sensor);

EnergySaving myPowSave;
RTC_SAMD21 myRtc;

#define PIN_LED 13

void setup()
{


  //configure gy-49 module (Ambient light sensor)
  Wire.begin(); //initialize library
  Serial.begin(9600); //start serial monitor
  Wire.beginTransmission(Address_GY49); //start wire iic transmission
  Wire.write(0x02); // Select configuration register
  Wire.write(0x40); // Continuous mode, Integration time = 800 ms
  Wire.endTransmission(); // Stop iic transmission
  delay(300);


  myRtc.begin();


  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH); //LED off (active LOW)

  myRtc.adjust(DateTime(2030, 4, 1, 8, 30, 0) );
  myRtc.attachInterrupt(dummyfunc);
  myPowSave.begin(WAKE_RTC_ALARM);

  myRtc.disableAlarm();
  DateTime timeNow = myRtc.now();
  const uint16_t uiAlmNextSec = 1000;
  DateTime timeAlarm = DateTime(timeNow.year(), timeNow.month(), timeNow.day(), timeNow.hour(), timeNow.minute(), timeNow.second() + uiAlmNextSec);
  myRtc.setAlarm(timeAlarm);
  myRtc.enableAlarm(myRtc.MATCH_SS);

}

void loop()
{
  // this executes
  for (int i = 0; i < 3; i++) {
    digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(1000);                       // wait for a second
    digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
    delay(1000);
  }

  //temperature sensor
  digitalWrite(LED_BUILTIN, HIGH);
  float objt = tmp006.readObjTempC();
  Serial.print("Object Temperature: "); Serial.print(objt); Serial.println("*C");
  float diet = tmp006.readDieTempC();
  Serial.print("Die Temperature: "); Serial.print(diet); Serial.println("*C");


  //gy-49 ambient light module
  unsigned int data[2];
  Wire.beginTransmission(Address_GY49); //start wire iic transmission
  Wire.write(0x03); // Select data register
  Wire.endTransmission(); // Stop iic transmission
  Wire.requestFrom(Address_GY49, 2); // Request 2 bytes of data
  // Read 2 bytes of data
  // luminance msb, luminance lsb
  if (Wire.available() == 2)
  {
    data[0] = Wire.read();
    data[1] = Wire.read();
  }
  // Convert the data to lux
  int exponent = (data[0] & 0xF0) >> 4;
  int mantissa = ((data[0] & 0x0F) << 4) | (data[1] & 0x0F);
  float luminance = pow(2, exponent) * mantissa * 0.045;

  // Output data to serial monitor
  Serial.print("Ambient Light Luminance :");
  Serial.print(luminance);
  Serial.println(" lux");

  delay(4300);

  myPowSave.standby();

  //proceed after wakeup


}

void dummyfunc()
{}

`
Does anyone have an idea what the problem could be? I am still quite new to Arduino so the solution might be super trivial. Also, I am unable to change the duration of the standby mode. The MCU says in standby mode for around about 50 seconds regardless of the uiAlmNextSec value. Anyone help will be much appreciated. Bless!

2

I would like to see a schematic, not a frizzy picture with links to "Technical" information on all the hardware parts. What do you do with the hardware when you go into standby? Pending the schematic I will take a SWAG and say you have to re initialize the I2C interface when waking up again.

1 Like
3

Perhaps this is a rare case where

 Serial.end();

would actually be used.

When you put everything to sleep, call it.

When you wake everything up, call

 Serial.begin(115200);

again.

Just from under the umbrella.

a7

1 Like
4

Thanks for the help. I found the reason today - once you use the RTC sleep method the USB clock is stopped, disabling the connection. No serial communication can take place.

5

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