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Interface Description Sensirion SCD30 Sensor Module
CO2, humidity, and temperature sensor
▪ NDIR CO
2
sensor technology
▪ Integrated temperature and humidity sensor
▪ Best performance-to-price ratio
▪ Dual-channel detection for superior stability
▪ Small form factor: 35 mm x 23 mm x 7 mm
▪ Measurement range: 400 ppm – 10.000 ppm
▪ Accuracy: ± (30 ppm + 3%)
▪ Fully calibrated with digital interface UART or I
2
C
Contents
1 Digital interface description
1.1 I2C Protocol
1.2 Modbus protocol
1.3 Sensor commands
1.4 Signal conversion to physical values
Revision History
Warning, Personal Injury
ESD Precautions
Warranty
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1 Digital interface description
The SCD30 digital interface is compatible with the I2C protocol and the Modbus protocol. For selecting Modbus protocol, the
SEL pin needs to be pulled to VDD Voltage. Please refer to datasheet.
1.1 I2C Protocol
Maximal I2C speed is 100 kHz and the master has to support clock stretching. Clock stretching period in write- and readframes is 12 ms, however, due to internal calibration processes a maximal clock stretching of 150 ms may occur once per day.
For detailed information to the I2C protocol, refer to NXP I2C-bus specification1. SCD30 does not support repeated start
condition. Clock stretching is necessary to start the microcontroller and might occur before every ACK. I2C master clock
stretching needs to be implemented according to the NXP specification. The boot-up time is < 2 s.
1.1.1 I2C Address
After power-up of the sensor, the I2C address of the prototype module is set to the address 0x61.
1.1.2 I2C Sequence
The commands issued by the I2C master are 16 bit with an optional parameter. Data sent to the master is protected by a
CRC. This also applies to data arguments sent to the sensor, please see chapter 1.1.3 for CRC checksum calculation. 2 byte
data sent from or received by the sensor is always succeeded with an 8 bit CRC. Examples are shown below.
I2C write 16bit command without arguments
Example: Stop measurements 0x0104
START 0xC2 0x01 0x04 STOP
(Red: Write Header; Blue: Read Header; Black: Data; Green: CRC; Start Condition: START; Stop Condition: STOP)
1
http://www.nxp.com/documents/user_manual/UM10204.pdf
S
W
I2CAddress
Cmd MSB
ACK
Cmd LSB
ACK
Clock
Stretching
P
ACK
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I2C write 16bit command with arguments
Example: Trigger continuous measurement (Pressure = 0mBar)
START 0xC2 0x00 0x10 0x00 0x00 0x81 STOP
(Red: Write Header; Blue: Read Header; Black: Data; Green: CRC; Start Condition: START; Stop Condition: STOP)
S
W
I2CAddress
Cmd MSB
ACK
Cmd LSB
ACK
Clock
Stretching
ACK
Data0 MSB
ACK
Data0 LSB
ACK
CRC0
P
or
Data1 MSB
ACK
Data1 LSB
ACK
CRC1
P
or
DataN MSB
ACK
DataN LSB
ACK
CRCN
P
ACK
ACK
ACK
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I2C read multiple 16bit words
Example: Read Measurement (example with 439 PPM, 48.8% RH, 27.2 °C)
START 0xC2 0x03 0x00 STOP START 0xC3 0x43 0xDB 0xCB 0x8C 0x2E 0x8F 0x41 0xD9 0x70 0xE7 0xFF 0xF5 0x42 0x43 0xBF
0x3A 0x1B 0x74 STOP
(Red: Write Header; Blue: Read Header; Black: Data; Green: CRC; Start Condition: START; Stop Condition: STOP)
S
R
I2CAdr[6:0]
Data0 MSB
ACK
Data0 LSB
NACK
Clock
Stretching
P
ACK
Data1 MSB
ACK
Data1 LSB
ACK
DataN MSB
ACK
DataN LSB
or
ACK
or
NACK P NACK
P
ACK
CRC0
ACK
CRC1
ACK
CRCN
S
W
I2CAdr[6:0]
Address MSB
ACK
Address LSB
ACK
Clock
Stretching
P
ACK
≈
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Table 1 I2C write and read communication frames. SDA is controlled by the I2C master in clear blocks and by the sensor in dark blocks.
1.1.3 I
2
C Checksum calculation
The checksum byte for I2C communication is generated by a CRC algorithm with the following properties:
Preceding Command
Value
Name
CRC-8
Protected Data
read data
Width
8 bits
Polynomial
0x31 (x8 + x5 + x4 + 1)
Initialization
0xFF
Reflect Input
false
Reflect Output
false
Final XOR
0x00
Example
CRC(0xBEEF) = 0x92
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1.2 Modbus protocol
For selecting Modbus protocol, the SEL pin needs to be pulled to VDD Voltage. Please refer to datasheet.
The supported baud rate is 19200 Baud with 8 Data bits, 1 Start bit and 1 Stop bit, no Parity bit.
More details on the Modbus protocol can be found here:
Description
Link
General introduction
http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf
Modbus frame generator
http://modbus.rapidscada.net/
Modbus CRC generator
https://www.lammertbies.nl/comm/info/crc-calculation.html
1.2.1 Modbus address
Modbus address is 0x61.
1.2.2 Modbus function codes
Available function codes are
Function code
Description
3
Read holding registers
4
Read input registers
6
Write single holding register
1.3 Sensor commands
The command set of the SCD30 is defined as follows. All commands are available via Modbus and I2C.
- Trigger continuous measurement with optional ambient pressure compensation
- Stop continuous measurement
- Set measurement interval
- Get data ready status
- Read measurement
- (De-)Activate continuous calculation of reference value for automatic self-calibration (ASC)
- Set external reference value for forced recalibration (FRC)
- Set temperature offset for onboard RH/T sensor
- Altitude compensation
- Soft reset
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1.3.1 Trigger continuous measurement with optional ambient pressure compensation
Starts continuous measurement of the SCD30 to measure CO2 concentration, humidity and temperature. Measurement data
which is not read from the sensor will be overwritten. The measurement interval is adjustable via the command documented in
chapter 1.3.3, initial measurement rate is 2s.
Continuous measurement status is saved in non-volatile memory. When the sensor is powered down while continuous
measurement mode is active SCD30 will measure continuously after repowering without sending the measurement command.
The CO2 measurement value can be compensated for ambient pressure by feeding the pressure value in mBar to the sensor.
Setting the ambient pressure will overwrite previous and future settings of altitude compensation. Setting the argument to zero
will deactivate the ambient pressure compensation. For setting a new ambient pressure when continuous measurement is
running the whole command has to be written to SCD30.
Protocol
Command (hex)
Argument
Description
I2C
0x0010 argument
Format: uint16 Available
range:
0 & [700 … 1200]. Pressure
in mBar.
Triggers continuous
measurement. Ambient
pressure is compensated by
setting argument. argument
= 0 deactivates pressure
compensation.
Protocol
Function Code
Address
Data to write
Modbus
6
0x0036
0x0000 or
pressure in
mBar
Full sequence examples:
Protocol
Data to write / read
Description
I2C
Start
Write
Header
Cmd
MSB
CMS
LSB
Pressure
MSB
Pressure
LSB
CRC
Stop
Stop
0xC2
0x00
0x10
0x00
0x00
0x81
Stop
Start continuous
measurement without
ambient pressure
compensation
Modbus
Request:
Slave
Addre
ss
Functi
on
Code
Addre
ss
MSB
Addre
ss
LSB
Conte
nt
MSB
Conte
nt
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x36
0x00
0x00
0x60
0x64
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x36
0x00
0x00
0x60
0x64
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1.3.2 Stop continuous measurement
Stops the continuous measurement of the SCD30.
Protocol
Command (hex)
Description
I2C
0x0104, no argument
Stops continuous
measurement.
Protocol
Function Code
Address
Data to write
Modbus
6
0x0037
0x0001
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
Stop
Stop
0xC2
0x01
0x07
Stop
Stops continuous
measurement.
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x37
0x00
0x01
0xF0
0x64
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x37
0x00
0x01
0xF0
0x64
1.3.3 Set measurement interval
Sets the interval used by the SCD30 sensor to measure in continuous measurement mode (see chapter 1.3.1). Initial value is
2 s. The chosen measurement interval is saved in non-volatile memory and thus is not reset to its initial value after power up.
Protocol
Command (hex)
Argument
Description
I2C
0x4600 argument
Format: unit16
Interval in seconds.
Available range:
[2 … 1800] given in 2 byte
in the order MSB, LSB.
Sets the interval for
continuous measurement
mode. Standard
measurement interval is 2.
Protocol
Function Code
Address
Data to write
Modbus
6
0x0025
argument
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
Interval
MSB
Interval
LSB
CRC
Stop
Stop
0xC2
0x46
0x00
0x00
0x02
0xE3
Stop
Set measurement interval
to 2s
Modbus
Request:
Slave
Addre
ss
Functi
on
Code
Addre
ss
MSB
Addre
ss
LSB
Conte
nt
MSB
Conte
nt
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x25
0x00
0x02
0x10
0x60
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x25
0x00
0x02
0x10
0x60
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1.3.4 Get data ready status
Data ready command is used to determine if a measurement can be read from the sensor’s buffer. Whenever there is a
measurement available from the internal buffer this command returns 1 and 0 otherwise. As soon as the measurement has been
read by the return value changes to 0.
It is recommended to use data ready status byte before readout of the measurement values.
Protocol
Address (hex)
Description
I2C
0x0202, no argument needed
Data ready status. Status
equals “1” when a
measurement is available to
be read from the sensor.
Protocol
Function Code
Address
Modbus
3
0x0027
Full sequence examples:
Protocol
Data to write/Read
Description
I2C
Write:
Start
Write
Header
Cmd
MSB
Cmd
LSB
Stop
Stop
0xC2
0x02
0x02
Stop
Read:
Start
Read
Header
Data
Ready
MSB
Data
Ready
LSB
CRC
Stop
Start
0xC3
0x00
0x01
0xB0
Stop
Reading Data Ready status
(returning 1)
Modbus
Request
Slave
Address
Function
Code
Address
MSB
Address
LSB
No. of
registers
MSB
No. of
registers
LSB
CRC
LSB
CRC
MSB
0x61
0x03
0x00
0x27
0x00
0x01
0x3D
0xA1
Response:
Slave
Address
Function
Code
No. of
Bytes
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x03
0x02
0x00
0x01
0xF9
0x8C
I2C: SDA is controlled by the I2C master in clear blocks and by the sensor in dark blocks.
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1.3.5 Read measurement
When new measurement data is available it can be read out with the following command. Make sure that the measurement is
completed by reading the data ready status bit before read out.
Protocol
Address (hex)
Description
I2C
0x0300, no argument needed
Reads a single
measurement of CO2
concentration.
Protocol
Function Code
Address
Modbus
3
0x0028 - 0x002D
Full sequence examples:
Protocol
Data to write/read
Description
I2C
Write:
Start
Write
Header
Cmd
MSB
Cmd
LSB
Stop
Stop
0xC2
0x03
0x00
Stop
Read:
Start
Read
Header
CO2
MMSB
CO2
MLSB
CRC
CO2
LMSB
CO2
LLSB
CRC
Start
0xC3
0x43
0xDB
0xCB
0x8C
0x2E
0x8F
T
MMSB
T
MLSB
CRC
T
LMSB
T
LLSB
CRC
0x41
0xD9
0x70
0xE7
0xFF
0xF5
RH
MMSB
RH
MLSB
CRC
RH
LMSB
RH
LLSB
CRC
Stop
0x42
0x43
0xBF
0x3A
0x1B
0x74
Stop
Example with sensor
returning:
CO2 Concentration = 439
PPM
Humidity = 48.8 %
Temperature = 27.2 °C
Modbus
Request
Slave
Address
Function
Code
Address
MSB
Address
LSB
No. of
register
s MSB
No. of
register
s LSB
CRC
LSB
CRC
MSB
0x61
0x03
0x00
0x28
0x00
0x06
0xCC
0x67
Response:
Slave
Address
Function
Code
No. of
Bytes
CO2
MMSB
CO2
MLSB
CO2
LMSB
CO2
LLSB
0x61
0x03
0x0C
0x43
0xDB
0x8C
0x2E
T
MMSB
T
MLSB
T
LMSB
T
LLSB
RH
MMS
B
RH
MLSB
RH
LMSB
RH LLSB
0x41
0xD9
0xE7
0xFF
0x42
0x43
0x3A
0x1B
CRC
LSB
CRC
MSB
0x50
0x07
SDA is controlled by the I2C master in clear blocks and by the sensor in dark blocks.
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Table 2 and Table 3 shows the data layout of the data read out from the sensor.
I2C read-out stream:
Using I2C for read-out the sensor will stream out the data in the given order.
Preceding Command
Consecutive read
Description
Read measurement
Byte1: CO2 concentration MMSB
Byte2: CO2 concentration MLSB
Byte3: CRC
Byte4: CO2 concentration LMSB
Byte5: CO2 concentration LLSB
Byte6: CRC
Byte7: Temperature MMSB
Byte8: Temperature MLSB
Byte9: CRC
Byte10: Temperature LMSB
Byte11: Temperature LLSB
Byte12: CRC
Byte13: Humidity MMSB
Byte14: Humidity MLSB
Byte15: CRC
Byte16: Humidity LMSB
Byte17: Humidity LLSB
Byte18: CRC
Data read-out table for I2C
communication. Measurement of CO2
concentration, humidity and temperature
has to be finished before read-out.
Table 2: I2C data read-out table. Read-out of measurement data can be aborted by sending a NACK followed by a stop condition
after any data byte.
Example: The CO2 concentration 400 ppm corresponds to 0x43c80000 in Big-Endian notation.
Modbus read-out stream:
Words for retrieving CO2 concentration, humidity and temperature can be read out at the following addresses. The words can
be read from the sensor in an arbitrary order.
Preceding Command
Consecutive read
Memory address
Description
Read measurement
Word0: CO2 MSW
Word1: CO2 LSW
Word2: Temperature MSW
Word3: Temperature LSW
Word4: Humidity MSW
Word5: Humidity LSW
0x0028
0x0029
0x002A
0x002B
0x002C
0x002D
Data read-out table for Modbus
communication. Measurement of CO2
concentration, humidity and temperature
has to be finished before read-out.
Table 3: Modbus data read-out table.
Example: The CO2 concentration 400 ppm corresponds to 0x43c80000 in Big-Endian notation.
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1.3.6 (De-)Activate Automatic Self-Calibration (ASC)
Continuous automatic self-calibration can be (de-)activated with the following command. When activated for the first time a
period of minimum 7 days is needed so that the algorithm can find its initial parameter set for ASC. The sensor has to be exposed
to fresh air for at least 1 hour every day. Also during that period, the sensor may not be disconnected from the power supply,
otherwise the procedure to find calibration parameters is aborted and has to be restarted from the beginning. The successfully
calculated parameters are stored in non-volatile memory of the SCD30 having the effect that after a restart the previously found
parameters for ASC are still present. Note that the most recently found self-calibration parameters will be actively used for selfcalibration disregarding the status of this feature. Finding a new parameter set by the here described method will always
overwrite the settings from external recalibration (see chapter 1.3.7) and vice-versa. The feature is switched off by default.
To work properly SCD30 has to see fresh air on a regular basis. Optimal working conditions are given when the sensor sees
fresh air for one hour every day so that ASC can constantly re-calibrate. ASC only works in continuous measurement mode.
ASC status is saved in non-volatile memory. When the sensor is powered down while ASC is activated SCD30 will continue with
automatic self-calibration after repowering without sending the command.
Protocol
Command (hex)
Argument
Description
I2C
0x5306 argument
Format: uint16
“1”: Activate continuous
ASC
“0”: Deactivate continuous
ASC
See notes above, feature is
switched off by default.
Protocol
Function Code
Address
Data to write
Modbus
6
0x003A
Argument
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
ASC
MSB
ASC
LSB
CRC
Stop
Stop
0xC2
0x53
0x06
0x00
0x00
0x81
Stop
Example: deactivate ASC
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x3A
0x00
0x00
0xA0
0x67
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x3A
0x00
0x00
0xA0
0x67
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1.3.7 Set Forced Recalibration value (FRC)
Forced recalibration (FRC) is used to compensate for sensor drifts when a reference value of the CO2 concentration in close
proximity to the SCD30 is available. For best results the sensor has to be run in a stable environment in continuous mode at a
measurement rate of 2s for at least two minutes before applying the calibration command and sending the reference value.
Setting a reference CO2 concentration by the here described method will always overwrite the settings from ASC (see chapter
1.3.6) and vice-versa. The reference CO2 concentration has to be within the range 400 ppm ≤ c
ref
(CO2) ≤ 2000 ppm.
FRC value is saved in non-volatile memory, the last set FRC value will be used for field-calibration after repowering.
Protocol
Command (hex)
Argument
Description
I2C
0x5204 argument
Format: uint16
CO2 concentration in ppm
See notes above.
Protocol
Function Code
Address
Data to write
Modbus
6
0x0039
Argument
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
FRC
MSB
FRC
LSB
CRC
Stop
Stop
0xC2
0x52
0x04
0x01
0xC2
0x50
Stop
Example: Set FRC with
argument
450 ppm
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x39
0x01
0xC2
0xD0
0x66
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x39
0x01
0xC2
0xD0
0x66
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1.3.8 Set Temperature Offset
The on-board RH/T sensor is influenced by thermal self-heating of SCD30 and other electrical components. Design-in alters the
thermal properties of SCD30 such that temperature and humidity offsets may occur when operating the sensor in end-customer
devices. Compensation of those effects is achievable by writing the temperature offset found in continuous operation of the
device into the sensor.
Temperature offset value is saved in non-volatile memory. The last set value will be used for temperature offset compensation
after repowering.
Protocol
Command (hex)
Argument
Description
I2C
0x5403 argument
Format: uint16
Temperature offset, unit
[°C x 100], i.e. one tick
corresponds to 0.01°C
See notes above.
Protocol
Function Code
Address
Data to write
Modbus
6
0x003B
argument
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
SHT Offset
MSB
SHT Offset
LSB
CRC
Stop
Stop
0xC2
0x52
0x04
0x01
0xF4
0x33
Stop
Example: Set temperature
offset to 5 K
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x3B
0x01
0xF4
0xF1
0xB0
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x3B
0x01
0xF4
0xF1
0xB0
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1.3.9 Altitude Compensation
Measurements of CO2 concentration based on the NDIR principle are influenced by altitude. SCD30 offers to compensate
deviations due to altitude by using the following command. Setting altitude is disregarded when an ambient pressure is given to
the sensor, please see section 1.3.1.
Altitude value is saved in non-volatile memory. The last set value will be used for altitude compensation after repowering.
Protocol
Command (hex)
Argument
Description
I2C
0x5102 argument
Format: uint16
Height over sea level in
[m] above 0.
See notes above.
Protocol
Function Code
Address
Data to write
Modbus
6
0x0038
argument
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
Altitude
MSB
Altitude
LSB
CRC
Stop
Stop
0xC2
0x51
0x02
0x03
0xE8
0xD4
Stop
Set altitude to 1000m above
sea level
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x38
0x03
0xE8
0x01
0x19
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x38
0x03
0xE8
0x01
0x19
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1.3.10 Soft reset
The SCD30 provides a soft reset mechanism that forces the sensor into the same state as after powering up without the need
for removing the power-supply. It does so by restarting its system controller. After soft reset the sensor will reload all calibrated
data. However, it is worth noting that the sensor reloads calibration data prior to every measurement by default. This includes
previously set reference values from ASC or FRC as well as temperature offset values last setting.
The sensor is able to receive the command at any time, regardless of its internal state. In order to start the soft reset procedure
the following command should be sent.
Protocol
Command (hex)
Argument
Description
I2C
0xD304
Restarts the sensor
Protocol
Function Code
Address
Data to write
Modbus
6
0x0034
0x0001
Full sequence examples:
Protocol
Data to write
Description
I2C
Start
Write
Header
Cmd
MSB
Cmd
LSB
Stop
Stop
0xC2
0xD3
0x04
Stop
Restarts the sensor
Modbus
Request:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x34
0x00
0x01
0x00
0x64
Response:
Slave
Address
Function
Code
Address
MSB
Address
LSB
Content
MSB
Content
LSB
CRC
LSB
CRC
MSB
0x61
0x06
0x00
0x34
0x00
0x00
0x00
0x64
www.sensirion.com Version 0.91 – D1 – August 2018 17/18
1.4 Signal conversion to physical values
All data read from the sensor are float numbers in big-endian format2. Conversion of digital values Sx, (x = c(CO2), RH, T) to
physical values and respective units are shown in the following table
Physical quantity
Conversion formula
Units
Range
CO2 concentration c(CO2)
c(CO2) = S
c(CO2)
ppm
0 – 10000
Temperature T
T = ST
°C
-40 – 125°C
Relative humidity RH
RH = SRH
%RH
0 – 100
Table 4: Signal conversion table.
Conversation of temperature to °F as well as relative humidity to absolute humidity and dew point temperature can be found in
Sensirion’s online support center3
Sample pseudo code for converting data read from the sensor to physical value can be found below.
// CO2 concentration
float co2Concentration;
unsigned int tempU32;
// read data is in a buffer. In case of I2C CRCs have been removed
// beforehand. Content of the buffer is the following
unsigned char buffer[4];
buffer[0] = 0x43; // MMSB CO2
buffer[1] = 0xDB; // MLSB CO2
buffer[2] = 0x8C; // LMSB CO2
buffer[3] = 0x2E; // LLSB CO2
// cast 4 bytes to one unsigned 32 bit integer
tempU32 = (unsigned int)((((unsigned int)buffer[0]) << 24) |
(((unsigned int)buffer[1]) << 16) |
(((unsigned int)buffer[2]) << 8) |
((unsigned int)buffer[3]));
// cast unsigned 32 bit integer to 32 bit float
co2Concentration = *(float*)&tempU32; // co2Concentration = 439.09f
2
IEEE 754 applies.
3
https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_at_a_Glance_V1.pdf
www.sensirion.com Version 0.91 – D1 – August 2018 18/18
1 Important Notices
1.1 Warning, Personal Injury
Do not use this product as safety or emergency stop devices or in any other application where failure of the product could result in personal
injury. Do not use this product for applications other than its intended and authorized use. Before installing, handling, using or servicing this
product, please consult the data sheet and application notes. Failure to comply with these instructions could result in death or serious injury.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify and hold harmless
SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages and expenses, and reasonable attorney
fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if SENSIRION shall
be allegedly negligent with respect to the design or the manufacture of the product.
1.2 ESD Precautions
The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD-induced damage and/or degradation, take
customary and statutory ESD precautions when handling this product.
See application note “ESD, Latchup and EMC” for more information.
1.3 Warranty
SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of delivery that this product shall be
of the quality, material and workmanship defined in SENSIRION’s published specifications of the product. Within such period, if proven to be defective,
SENSIRION shall repair and/or replace this product, in SENSIRION’s discretion, free of charge to the Buyer, provided that:
▪ notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;
▪ such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design, material, or workmanship;
▪ the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; and
▪ the warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period.
This warranty does not apply to any equipment which has not been installed and used within the specifications recommended by SENSIRION for the intended
and proper use of the equipment. EXCEPT FOR THE WARRANTIES EXPRESSLY SET FORTH HEREIN, SENSIRION MAKES NO WARRANTIES, EITHER
EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT. ANY AND ALL WARRANTIES, INCLUDING WITHOUT LIMITATION, WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE EXPRESSLY EXCLUDED AND DECLINED.
SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper use of the goods.
SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated or stored not in accordance with the
technical specifications.
SENSIRION does not assume any liability arising out of any application or use of any product or circuit and specifically disclaims any and all liability, including
without limitation consequential or incidental damages. All operating parameters, including without limitation recommended parameters, must be validated
for each customer’s applications by customer’s technical experts. Recommended parameters can and do vary in different applications.
SENSIRION reserves the right, without further notice, (i) to change the product specifications and/or the information in this document and (ii) to improve
reliability, functions and design of this product.
Copyright© 2017, by SENSIRION.
CMOSens® is a trademark of Sensirion
All rights reserved
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info@sensirion.com
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