IAQ-ENGINE

Manual iAQ-engine, Version 2.0 May 2011 (all data subject to change without notice) Manual iAQ-engine Indoor Air Quality sensor • • Digital and analog I/O SMD type package Product summary iAQ-engine is used for measuring VOC levels that can be read out as a prediction via the I2C bus. The iAQengine can also control equipment directly by an analog output with a 0-5 V DAC. The sensor itself is protected by a plastic cap and a filter membrane. The sensor module can be soldered directly to a host circuit board with selective soldering. Dimensions 7.6 12.3 1 6 2 5 3 4 Pin 1 2 3 4 5 6 17.8 2.54 4.9 Name PRED SCL GND SDA NC VCC Comment Prediction I/O Serial clock Ground Serial data Not connected +5V 11.2 PCB 15.24 x 17.78 mm 15.2 HEIGHT PCB 1.7 mm Figure 1: iAQ-engine sensor (dimensions in mm, Top View) Dimensions (approximate values) HOOD 11.2 x 17.78 mm TOTAL HEIGHT 4.3 mm Sensor position (approximate values) 7.6 x 12.3 mm Weight Approximately 1g IP-Class 00 Connector Card edge (cut via) 1 Radius 3,5 mm Manual iAQ-engine ( all data subject to change without notice) 1 Electrical specifications 1.1 Power supply Voltage 5.0 ± 0.25V, max. 20mV ripple Power consumption 225mW @ 5.0VDC Note: Module features a decoupling capacitor. 1.2 Communication 2 IC Output signal options DAC (0-5)V First functional reading after start up 15 minutes
For more communication details see chapter 4 2 Environmental Temperature range operation 0 to 50°C Temperature range storage -25 to 50°C Humidity range 5 to 95 %r.h., non-condensing 3 Sensor Features Sensing technology MEMS metal oxide sensor Sensing range I²C: 450 – 65535 ppm CO2 equivalents (relative) DAC: 450 – 2000 ppm CO2 equivalents (relative) Module Automatic baseline correction 2 Manual iAQ-engine ( all data subject to change without notice) 4 I²C Interface 4.1 Interface description 4.1.1 Physical interface The physical interface is two-wire open drain SCL (clock) and SDA (data). Pull-up resistors External pull-up resistor required Clock speed 100kHz Clock stretching Bus master clock stretching support is required 4.1.2 Clock stretching Clock stretching pauses a transaction by holding the clock line low. The transaction cannot continue until the line is released to high again. Although the module could send the bytes of data at a fast rate, it could happen that the module is busy at the request time. It can then hold the clock line low after reception and acknowledgement of a byte to force the master into a wait state until the iAQ-engine module is ready for the next byte transfer in a type of handshake procedure. (See official I²C specification and user manual UM10204, http://www.nxp.com/documents/user_manual/UM10204.pdf) 4.1.3 Address 2 Standard 7 bit I C address for iAQ-engine is decimal 90 or hexadecimal 0x5A. The addressing byte includes the read/write bit at the lowest significant bit. The communication with the iAQ-engine starts with 0xB5 for reading data. Address R/ W Bit 7 6 5 4 3 2 1 0 data 1 0 1 1 0 1 0 1 Table 1: Addressing byte for the iAQ-engine 4.2 Interface protocol The standard I²C specification is used for the iAQ-engine interface protocol. The I²C bus master should request 7 bytes. These seven bytes include information about the indoor air quality value, the iAQ-engine status and the resistance of the sensor. If there is a need just for the indoor air quality value and the status, the master should request three bytes from the iAQ-engine. All bytes are reported back as shown in the following table. A graphical description for a standard I²C communication with the iAQ-engine module is shown in figure 2 – figure 5. Byte 0-1 Name pred Data type uint16 Typical/example value 450 2 status uint8 0 3-6 resistance int32 256431 Table 3: Read data from the iAQ-engine 3 Explanation / notes Prediction [ppm] 0x00: OK (data valid) 0x01: BUSY (re-read multi byte data!) 0x80: ERROR (if constant:replace sensor) Sensor resistance [Ohm] Manual iAQ-engine ( all data subject to change without notice) Figure 2: The first byte is send by the master, containing address (0x5A) and read/write bit. The slave sends an acknowledgement (ACK) by pulling the data line to low. Figure 3: The slave will answer by sending bytes with MSB first. Byte0 and byte1 contain the prediction value. All bytes are Acknowledged by the master. Figure 4: The third byte contains the information of the iAQ-engine module state, in this case status = 1. The master answeres with an Acknowledge. 4 Manual iAQ-engine ( all data subject to change without notice) Figure 5: The last four bytes contain the resistance value. For the calculation of the resistance only byte4, byte5 and byte 6 are relevant, because byte3 is zero .After the last requested byte, the master sends a not Acknowledge. 4.2.1 Prediction Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 The first two bytes contain the prediction value, which gives the information about the indoor air quality. The value is a CO2 equivalent and the calculation is shown in the following example. Equation 1 : 5 Manual iAQ-engine ( all data subject to change without notice) 4.2.2 Status Flag Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6 The third byte indicates status of the module. • 0x00: OK • 0x01: BUSY • 0x80: ERROR If status is OK the data is valid. If the status is BUSY, the data integrity is not guaranteed for variables of size > 8 bits, because the module may be updating a part of the variable. If the status is ERROR constantly (or very frequently) this indicates that the module is reading non-realistic values, and the sensor element is probably defective. 4.2.3 Resistance Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 The next four bytes contain the sensor resistance in Ohm. The fourth byte of the int32 variable is 0. Equation 2: 4.3 Typical applications VCC_________ 4k7 Microcontroller 4k7 SCL iAQ-engine GND SDA Figure 6: Simple microcontroller application 6 Byte6 Manual iAQ-engine ( all data subject to change without notice) 4.4 Recommended footprint 15.2 2.54 1.4 Keep out 2.54 Figure 7: Recommended footprint (standard) 4.5 Ordering information Order code 60-0100 Comment iAQ-engine 7