part 1
Project description
Figure 1 shows the Zigbee gas detector boards, the left board holds the analog part with an XBee module connector while the right board is the digital board with avr32 module AL-UC3AEB MCU, oscillator and regulators, this board was bought from http://alvidi.de/avr32_module.html

Figure 1: to the left analog board with XBee socket,to the right digital board with avr32 MCU

The device works when the two boards are packed together back to back (see figure 2) and power is fed from 5V usb cable. In the XBee configuration the usb cable is used only for power and not for data, other configuration can use the usb cable both for power and data (in this case the XBee module is disabled).

Figure 2: working device top view, the analog board is over the digital board.

The analog sensors MQ-4, MQ-7 are continuously fed with 5V to keep them at working temperature (this is why it can not be used as an end device). Every 100 msec the MCU samples the analog sensors and stores the results, other tasks are responsible for running the algorithm over the data and broadcasting when the buffer is full over the air (if requested), for more details see the digital board description.
A simple Matlab gui is used to show gas and temperature measurements and device messages, for more details see gui section.