SafeSense v1.0: A Wireless Environmental-Monitor Project

SafeSense BD

I thought I smelled gas coming from my fireplace one evening. After inspection I was assured there was not an issue and the smell was aging pipes. The experience led me to the realization however that there was no natural gas monitoring in my home. A few block diagram iterations later and I had designed a wireless sensor node with the following requirements:

1. Monitor natural gas *
2. Monitor carbon monoxide **
3. Temperature and humidity monitoring for sensor calibration and temp gradient measurements
4. Report measurements wirelessly, 915MHz ISM band (chosen for range, low data bandwidth, and antenna requirements)
5. Optional vibration sensor (for significant earthquake event reporting)
6. Optional geophone sensor (for minor earthquake event reporting)

BOM Highlights:

MRF49XA-I/ST: 415/915MHz XCVR chip from Microchip. Selected for cost, range, modulation diversity, spectral occupancy. Although wireless standards already exist (X-Bee) I will be developing a protocol for multiple node integration with low interference.

MQ-4: Natural Gas sensor or equivalent.

: For temperature and humidity monitoring at each node; calibration of gas sensors.

ATMEGA328-AUR: Standard AVR chosen for rapid code development. A PIC would be a more cost effective solution in an actual product.

The prototype PCB arrived last weekend, bring-up to occur in the following sequence:

Bring-Up Sequence

1. Power supplies (passed)
2. AVR (wip)
3. Natural gas sensor (already prototyped)
4. Wireless XCVR
5. Base Station XCVR (Prototype = Arduino Yun with MRF49XA Shield I also fabbed)
5. Temperature/Humidty Sensor
6. Calibration Curves
7. Remainder of sensors as deemed necessary

In all the project is more to satisfy curiosity and creative urges. Moreover it is an exercise in sensor integration, coordination of wireless nodes on one frequency, and handling of data/metrics from multiple nodes and creating trends, warnings, etc. The central hub of the network is TBD, however it will feature a 915MHz ISM XCVR as well and an Ethernet interface.

Assembly and Bringup PS_ARD

* Not intended to replace regular servicing and maintenance of gas-based appliances; simply an additional safety monitor
** Does not replace CO monitor required by CA-law for each level of the home


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