Wireless Air Quality Monitoring
Wireless air quality monitoring is a challenge. Most chemical sensors are not precise enough and require power hungry heating, which would require huge energy reserves if used wirelessly. For example XEMICS and MICROSENS have developed a wireless air quality sensing solution based on the XEMICS XE88LC05, XM1201A and Microsens MSGS3000 sensing element.
MSGS3000 heating is achieved with low power as the sensing part is very small. The data acquisition, processing and communication formatting is handled by the XEMICS’ system on chip. In this application, it is used to bias the heating element of the sensors with the correct waveform, to read the sensors value, and to send the corresponding data to an XM1201A transceiver. The XM1201A low-power ISM band transceiver then transmits the data over 100 m with just 10 mA, and it spends most of the time in sleep mode.
Sensor integration, system-on-chip data acquisition and low power transmission makes this system very low cost and miniature compared to previous technologies.
Figure 1: Wireless Gas Sensor Schematics
The XM1201A (available from XEMICS) is made of one XE1201A, the antenna and a few passive components. It is sold ready to send-receive. The software is available from XEMICS, and should be customized for the final application by the customer.
The MGSM3000 (available from Microsens) is made up of two MSGS3000 gas sensors, one KTY13-5 temperature sensor, one XE88LC05MI028 acquisition system, one MAX232 level shifter, one Xtal and one voltage reference. As all the sensor’s management is done inside the MGSM3000, one can even program the included XE88LC05 for direct action via its parallel IO port.
The MSGS3000 gas sensor is made of 2 resistors built on a thin micro-machined silicon bridge. One resistor, named heater, is used to heat the second resistor, named sensing element, between 50?C and 500?C, depending on the measurement principle.
The sensing element resistivity depends on temperature and gas concentration. Reactivity of the sensing element also depends on temperature. Therefore an acquisition cycle uses several different temperatures of the two sensors to get accurate gas discrimination and gas concentration data. Figure 2 plots one example of a MSGS3000 sensitivity curve.
XEMICS’ XE88LC05 data acquisition SoC
The XEMICS’ XE88LC05 system-on-chip is a low-power, mixed signal microcontroller Unit (MCU) complete with a versatile 16+10 bits ZoomingADC? (best of SensorsExpo 2000 award in Anaheim), with programmable offset and gain pre-amplifier, plus 2 Digital to Analog Converters (DAC). Utilizing the very efficient CoolRISC? processor core, the XE88LC05 provides low-power, low-voltage solutions for sensing applications. The XE88LC05 is available with 100 years MTP Flash retention at 55?C on chip.
Figure 2: ZoomingADC?
The ZoomingADC? is a mix between amplifiers and ADC, together with a smart offset cancellation and offset suppression algorithm. The ZoomingADC?, with its very important dynamic range (16 + 10 bits) is perfectly adapted for this type of applications. Many different solutions can be implemented on the same board, just by reprogramming the integrated flash memory.
XM1201A transceiver module
The XM1201A is a general-purpose ISM band complete transceiver module. It is built around the low-power XE1201A transceiver chip. The XEMICS’ XE1201A is a half-duplex FSK transceiver for operation in the 433 MHz ISM band (optimized) and in the 300-500 MHz band. With its highly integrated architecture, no external filters are needed. This chip can equip both sensors as well as central units in sensing applications. The XE1201A has secure bi-directional transmission, suitable for voice over RF. It combines highest data throughput in its class with lowest power consumption, data rate up to 64 kbit/s and RX=6mA, TX=13mA@+5dBm.
With its high sensitivity the XE1201A is ideal for telemetry, RF security systems and wireless sensing. It can also be used in other security applications like door openers and remote controls. Needing few external components the XE1201A enables OEMs to develop cost/performance optimised solutions. With a glueless interface to the XE8000 family of mixed signal microcontrollers the XE1201A can be integrated with the ZoomingADC?, and have point-to-point or point-to-multipoint communications.
XEMICS XE8000 series is ideal for use with Internet connectivity. A demo has been developed based on the XEMICS Sensing Machines and the XEMICS transceivers. This smart house demo presents sensing and control applications, combining RF wireless with Internet connectivity.
1) XE88LC05 and XM1201A: www.xemics.com
2) AN8000.11 Application Note: Wireless Gas Sensor: www.xemics.com
3) MSGS3000 and MGSM3000: www.microsens.ch
XEMICS is a privately owned fabless semiconductor company with headquarters in Switzerland and a worldwide sales and customer support network. XEMICS delivers a range of advanced short-range wireless connectivity solutions to a global customer base. XEMICS is a leading designer and provider of Wireless RF transceivers and Bluetooth? applications, data acquisition, communication products, CODEC’s and GPS receivers. With a focus on high-quality low cost solutions XEMICS provides a combination of ultra-low power technology and innovative IC design.
XEMICS offers the XE8000 Sensing Machines, a series of low-power miniaturized System-on-Chip (SoC) with direct connection to resistive sensors for home security applications like fire detection, intrusion detection and air quality monitoring. These can also be used in home comfort applications like HVACs, remote controls and automatism as well as home metering applications. The XE8000 sensing machines can be used in conjunction with the XEMICS’ radio transceivers the XE1201A and XE1202 for RF connectivity.