A Sensing node consists of methane gas sensor, carbon monoxide gas sensor, accelerometer sensor, temperature sensor and RS232 interface circuit with dual port RAM. Methane gas sensor and carbon monoxide gas sensors are placed on stationary node because its concentration is lighter than so it detects near the roof of the mine. The purpose of using accelerometer is to detect the earth quake type of activities. The Sensing node gets data from neighbouring Sensing node and sends its data to the next Sensing node.
The main computing microcontroller in this Hardware is CC430F6137. There are various gas sensors connected to Sensing node which will help monitor explosive and toxic gases within the mine environment. To monitor any structural change in the mine the Sensing node will analyze accelerometer data and to prevent any fire it will also monitor temperature inside the mine.
There are number of sensors connected to the microcontroller as shown in figure 5.The data of some of these sensors will be captured by built-in 12 bit ADC inside the CC430f6137.To extend the addressable memory an external SRAM has been connected via SPI interface whereas Accelerometer is connected via I2C bus.
The complete schematic design of Sensing node comprises of 3 sheets which are connected with each other using off sheet connectors. The first sheet has a main computing unit of CC430 with CO sensor circuit, Methane gas sensor, Accelerometer and battery monitoring circuit. The second sheet has a RF matching circuit for CC430 RF Radio Core and the 3rd sheet has a power supply circuit for power-up all the modules.
schematic design of Sensing node. The gas sensor output is connected to the voltage clipping circuit because the A/D of CC430 can read maximum of 3.3V and gas sensors output varies from 0V-5V.The Output of clipping circuit is connected to CC430 via A/D convertor. The A/D reads the output of Methane and CO gas sensor and translates its voltage level to the respective gas concentration. The Accelerometer is connected to CC430 via I2C interface. The battery monitoring circuit output is connected to A/D of CC430. A/D read the value of voltage from battery monitoring circuit and displays the status of the battery on respective LED. A 1Kbit of SRAM is included to stationary node due to insufficient internal memory of CC430.
Following is the power supply circuit diagram supplying +3.3V and +5.0V
During testing we were able to send and receive data at a distance of 100 meters with RF power output of +12dbm
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