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3.4.1 start_continuous_measurement

The start_continuous_measurement command will start a continuous measurement.

Command

Command

Hex Code

Argument

Read Data

Execution

Time (ms)

Description

start_continu

ous_measure

ment

0x218B

-

-

-

Starts continuous

measurement with 1 s

sampling interval.

Recommended operation sequence:

1. Send the start_continuous_measurement command.

2. Wait 1 s13.

3. Send the read_measurement command (Section 3.4.3) and wait the specified execution time.

4. Read out the measurement data.

4.1. If data is not yet available, wait 150 ms and retry to read out the measurement data.

5. Wait 1 s13.

6. Repeat steps 3-5 as needed.

7. To stop the continuous measurement, send the stop_continuous_measurement command (Section 3.4.2)

and wait the specified execution time.

3.4.2 stop_continuous_measurement

The stop_continuous_measurement command will finish the currently running measurement before returning

to idle mode. During the execution time, the sensor will not acknowledge its I2C address nor accept commands.

Command

Command

Hex Code

Argument

Read Data

Execution

Time (ms)

Description

stop_continuo

us_measurem

ent

0x3F86

-

-

1’200

Stops the continuous

measurement and put the

sensor into idle mode.

3.4.3 Read_measurement

Measurement data is read out through the read_measurement command. The measurement data buffer is

emptied upon read-out. Subsequent measurement data can be readout by sending the sensor’s I2C address

and the read direction bit. The sensor will respond with a NACK if no measurement data is available. The

I2C master can abort the read transfer with a NACK followed by a STOP condition after any data byte. See

Section 3.5 for the signal output and input conversion. The sensor status is used to determine if the sensor is

in testing mode (See Section 3.4.13).

Command

Command

Hex Code

Argument Read Data

Execution

Time (ms)

Description

read_measur

ement

0xEC05

-

Byte0: CO2 concentration 8msb

Byte1: CO2 concentration 8lsb

Byte2: CRC

Byte3: Temperature 8msb

Byte4: Temperature 8lsb

Byte5: CRC

Byte6: Relative Humidity 8msb

Byte7: Relative Humidity 8lsb

Byte8: CRC

Byte9: Sensor Status 8msb

Byte10: Sensor Status 8lsb

Byte11: CRC

1

Reads out the

measurement data.

Values for temperature

and humidity are

provided as received from

the external temperature

and humidity sensor.

13

Note that the sensor and the microcontroller are subject to clock tolerances. The effective sampling interval is 1’000 ms ± 150 ms.