CO2-Sensor
Von Senseair:
Link zum Sensor
Kommunikation über I2C
Anschluss am I2C-Port des Controllers mit 1.2K- Pullup nach +3.3V
Beim K33 muss der Wert noch mit 10 multipliziert werden.
Testprogramm für CO2-Sensor:
Auslesen des Sensors und Daten über serielle Schnittstelle an einen PC schicken
'CO2-Messung<
'Sensor an I2C
'PC.5 = SCL
'PC.4 = SDA
$crystal = 8000000
$regfile = "m8def.dat"
$hwstack = 50
$baud = 9600
'Enable Urxc
'Enable Interrupts
'On Urxc Rscommand
Config Portd.5 = Output 'LED
'I2C
Config Sda = Portc.4
Config Scl = Portc.5
'CO2-Sensor
Dim Sensorstatus As Byte
Dim Sensorvalue As Word
Dim Sensorvalue_h As Byte At Sensorvalue Overlay
Dim Sensorvalue_l As Byte At Sensorvalue + 1 Overlay
Dim Sensorchecksum As Byte
Dim Secs As Long
'-------------------------------------------------------------------------------
Main:
Do
Secs = Secs + 1
Gosub Measureco2
Print Secs;
Print Chr(9);
Print Sensorvalue;
Print Chr(9);
If Sensorstatus = 1 Then Print "OK" Else Print "Error"
Waitms 1000
Loop
'-------------------------------------------------------------------------------
Measureco2:
'Senseair K30-Sensor über I2C ansprechen
'auf Fehler prüfen (Sensor nicht bereit) durch Auslesen des Statusbytes
'falls nicht bereit: Sensorstatus =0, falls Ok: 1
I2cstart
I2cwbyte 0
I2cstop
Waitms 1
I2cstart
I2cwbyte &HD0 'Adresse (&h68 1 Bit nach links, Bit0=R/W=0 (schreiben)
I2cwbyte &H22 'Read RAM 2 Bytes
I2cwbyte &H00 'Adresse H
I2cwbyte &H08 'Adresse L
I2cwbyte &H2A 'Checksum
I2cstop
Waitms 20
I2cstart
I2cwbyte &HD1 'Lesen an Adresse &h68
I2crbyte Sensorstatus , Ack
I2crbyte Sensorvalue_l , Ack
I2crbyte Sensorvalue_h , Ack
I2crbyte Sensorchecksum , Nack
I2cstop
Sensorstatus = Sensorstatus And 1
Return
Unterlagen von Senseair zur Programmierung
10.1. Example: Reading of CO2 value from sensor
To read the current CO2 concentration from the sensor we need to read memory locations 0x08 (hi byte) and 0x09 (low byte). To do this we need to send a sequence of two I2C frames: first we send an I2C write frame containing the sensor address, command number and how many bytes to read, RAM address to read from, and a checksum. Then we send an I2C read frame to read the status, data and checksum. See chapter 2 for details. In our case we want to read 2 bytes starting from address 0x08. This will give us data from address 0x08 and 0x09, which contains current CO2 reading. The sensor address is 0x68 (default factory setting, configurable in EEPROM). So, the first frame should look like:
Start | 0xD0 | 0x22 | 0x00 | 0x08 | 0x2A | StopA. a. 0xD0 is Sensor address and read/write bit. 0x68 shifted one bit to left and R/W bit is 0 (Write).
B. b. 0x22 is command number 2 (ReadRAM), and 2 bytes to read
C. c. Checksum 0x2A is calculated as sum of byte 2, 3 and 4.
II.
The next frame will read the actual data:
Start | 0xD1 | <4 bytes read from sensor> | Stop
A. d. The 1:st byte from the sensor will contain operation status, where bit 0 tells us if the read command was successfully executed.
B. e. The 2:nd and 3:rd byte will contain CO2 value hi byte and CO2 value low byte.
C. f. The 4:th byte contains checksum
D.
E.
F. 10.2. Example: Start background and zero calibration with I2C commands
III.
In K30 and K50 meters it is possible to start zero and background calibrations with I2C commands.
Background calibration for K30 meters look like this:
Start | 0xD0 | 0x12 | 0x00 | 0x67 | 0x7C | 0x06| 0xFB | Stop
A. a. 0xD0 is Sensor address and read/write bit. 0x68 shifted one bit to left and R/W bit is 0 (Write).
B. b. 0x12 is command number 1 (WriteRAM), and 2 bytes to write
C. c. 0x7C06 is background calibration command
D. d. Checksum 0xFB is calculated as sum of byte 2-6.
Zero calibration for K30:
I2C comm guide 2_10.doc Page 29 of 33
Start | 0xD0 | 0x12 | 0x00 | 0x67 | 0x7C | 0x07| 0xFC | Stop
1. e. 0xD0 is Sensor address and read/write bit. 0x68 shifted one bit to left and R/W bit is 0 (Write).
2. f. 0x12 is command number 1 (WriteRAM), and 2 bytes to write
3. g. 0x7C07 is background calibration command
4. h. Checksum 0xFC is calculated as sum of byte 2-6.
In K50 meters with memory map 8 or lower the zero and background commands are identical to K30 meters. In K50 meters with memory maps higher than 8 the address to write to is moved from 0x67, 0x68 to 0x32, 0x33.
Table 11 Measured value and status
