Duty cycling mode

What this example shows

Saving power by letting the sensor measure only now and then. In duty cycling mode the BMV080 measures, sleeps for the rest of a period you set, and delivers one reading per period. This example sets a 20 second period and prints PM2.5 each time a reading arrives.

The trade-off is in the datasheet: duty cycling always uses the fast response measurement algorithm, and the precision figures for continuous mode do not apply to it. The period has to be at least 2 seconds longer than the integration time, which is 10 seconds by default.

The example code

This is DutyCycle.ino from the pinned library, without its header comment. The sketch itself is exactly as shipped. It uses the board's default address, 0x57.

Select Board

DutyCycle.ino

 #include "BMV080-SOLDERED.h"

 BMV080 bmv080;             // Create an instance of the BMV080 class
 #define BMV080_ADDR 0x57   // BMV080 default address

void setup()
{
  Serial.begin(115200);

  while (!Serial) delay(10);  // Wait for Serial to become available

  Wire.begin();

  // Attempt to initialize the sensor via I2C
  if (bmv080.begin(BMV080_ADDR, Wire) == false) 
  {
    Serial.println("BMV080 not detected");
    while (1)
    ;
  }
  Serial.println("BMV080 found!");

  // Initialize the sensor
  if (bmv080.init())
  {
    Serial.println("BMV sensor initialized");
  }
  else
  {
    Serial.println("BMV initialization failed");
    while (1)
    ;
  }

  // Set the sensor Duty Cycling Period (seconds)
  uint16_t duty_cycling_period = 20;

  if(bmv080.setDutyCyclingPeriod(duty_cycling_period) == true)
  {
    Serial.println("BMV080 set to 20 second duty cycle period.");
  }
  else
  {
    Serial.println("Error setting BMV080 duty cycle period.");
  }

  // Set the sensor mode to Duty Cycle mode
  if(bmv080.setMode(BMV080_MODE_DUTY_CYCLE) == true)
  {
    Serial.println("BMV080 set to Duty Cycle mode");
  }
  else
  {
    Serial.println("Error setting BMV080 mode");
  }
}

void loop()
{
  // Attempt to get reading
  if (bmv080.readSensor())
  {
    float pm25 = bmv080.PM25();

    Serial.print(pm25);

    if (bmv080.isObstructed() == true)
    {
      Serial.print("\tObstructed");
    }

    Serial.println();
  }
  delay(1000);
}

Expected result, from a bench run on this board (the run did not record which controller it used):

Serial MonitorAutoscrollShow timestampNewline115200 baud

Message (Enter to send message to the board)

BMV080 found!
BMV sensor initialized
BMV080 set to 20 second duty cycle period.
BMV080 set to Duty Cycle mode
7.31
7.08
6.94

After the setup lines comes one line per period, about every 20 seconds, with the PM2.5 value in µg/m³ on its own, followed by Obstructed when the sensor's view is blocked. Your numbers depend on the air around the sensor.

Functions used

BMV080()returns None

Creates the sensor object. It takes no arguments: the address and the Wire port are given to begin().

ReturnsConstructor; no return value.

begin(const uint8_t address = BMV080_DEFAULT_ADDRESS, TwoWire &wirePort = Wire)returns bool

Sets the I2C address and Wire port the library uses and checks that the sensor answers at that address. It does not start the I2C bus, so call Wire.begin() first, as the example does.

Returnstrue when the sensor answered at the address, false otherwise.

Parameters

Name	Type	Description
address	uint8_t	The sensor's I2C address. Defaults to BMV080_DEFAULT_ADDRESS, which is 0x57, the board's default.
wirePort	TwoWire &	The I2C port to use. Defaults to Wire.

init()returns bool

Prepares the sensor through the Bosch driver: reads the driver version, opens the sensor, performs a soft reset and reads the sensor's ID. Call it after begin() and before anything else.

Returnstrue when every step succeeded, false when one failed.

setDutyCyclingPeriod(uint16_t duty_cycling_period)returns bool

Sets how long one duty cycle lasts: the measuring time plus the sleep time. Call it before setMode(), because the sensor takes its settings when the measurement starts. The Bosch default is 30 seconds.

Returnstrue when the period was set, false otherwise.

Parameters

Name	Type	Description
duty_cycling_period	uint16_t	The period in seconds. It must be at least 2 seconds longer than the integration time.

setMode(uint8_t mode)returns bool

Starts measuring in the mode you choose. In duty cycling mode the library gives the Bosch driver millis() as its clock.

Returnstrue when the Bosch driver started the measurement, false otherwise.

Parameters

Name	Type	Description
mode	uint8_t	BMV080_MODE_DUTY_CYCLE for duty cycling, as here, or BMV080_MODE_CONTINUOUS for continuous measurement.

readSensor(bmv080_output_t *bmv080_output = nullptr)returns bool

Lets the Bosch driver fetch and process data from the sensor once. When a new reading arrives, the library keeps it for PM25() and isObstructed(). In duty cycling mode the driver has to be serviced at least once a second, which the example's one-second loop does.

Returnstrue when a new reading arrived during this call, false otherwise.

Parameters

Name	Type	Description
bmv080_output	bmv080_output_t *	Optional. A Bosch output structure to copy the new reading into. The example leaves it out.

PM25()returns float

Returns the PM2.5 value of the latest reading: particles 2.5 µm across or smaller.

ReturnsPM2.5 mass concentration in µg/m³.

isObstructed()returns bool

Returns the obstruction flag of the latest reading. The sensor sets it when a fixed object sits in its optical path.

Returnstrue when the latest reading was obstructed, false otherwise.

Putting it together

Set the period first, then start duty cycling with setMode(). Keep calling readSensor() at least once a second: it returns true once per period. The sensor's interrupt output cannot trigger readings in this mode, so poll it as the example does.

SourceOpen the verified Arduino exampleView the exact source used by this page.examples/DutyCycle/DutyCycle.ino