The key features of the system are listed in the following mini spec sheet:
- Open-ended: can be extended and customized as needed to meet the user's requirements. The objective is to free it from 'lock-in' to particular hardware or software as much as possible.
- Provides both monitoring and control of the home:
- It will allow various temperatures and home status information like A/C power, water leaks, door open/closed, etc. to be read remotely (from anywhere in the world either cell phone service or an internet connection is available.)
- It will allow remote control of home lighting, temperatures, etc.
- Wireless to provide maximum reliability when land-lines go down, as they frequently do in our rural area.
- Does not require an internet connection in the home being monitored.
- Low-cost to build and operate. Remote access devices include cell phones, smart phones and browsers.
- Provides maximum flexibility in communicating via twitter, email and cell phone text messages from almost anywhere in the world.
- Remotely accessible functions are customizable by the user to include other functions, such as querying the temperature database recorded during operation to find things like maximum indoor temperatures over a multi-day period.
- Additional sensors and control devices can be easily added by the user.
- Based on open source hardware and software as much as possible
To achieve these goals the system is based on cell phone technology and uses text messages, otherwise known as short message service (SMS) to communicate all home information. This limits the quantity of information that can be transferred, in particular pictures and video of the home cannot be provided, but makes full internet access unnecessary, lowering operating costs and potentially increasing reliability. (I can get 1000 text messages for $10, and unlimited for $20 using my AT&T account.) Text messages can be sent to the monitor as email, using addresses like 4435550707@att.net, allowing for sending status requests and control commands via email, and receiving responses. Text messages can be sent to twitter accounts from the monitor, allowing periodic tweets of home status. And of course can be sent and received via cell phones and smart phones.
The system is based on open source software, from the operating system (the Pupeee version of Linux) to the programming language tools (Tcl/Tk.) It uses a currently inexpensive GSM USB modem (Icon 322 for about $30), a net book (the Asus 701, available for maybe $20 on eBay) and the open source Arduino microcomputer ($30 or so.) Wired to the microcomputer are various power and temperature sensors, and controls like light switches.
The most basic quantities we would like to know are the inside and outside temperatures, and whether house power is on or off. Power failures are not infrequent in our rural location, and can lead to ugliness when the contents of refrigerators and freezers eventually rots. Water leaks are another situation that can be expensive to repair, and a water sensor is a high priority, although I did not implement one in my first designs.
Monitoring systems are available commercially, but I wanted one that could be endlessly customized by adding sensors, remotely controlled switches and remotely accessed software to perform open-ended functions in the house. My hope is that others can benefit from my experiences in building their own systems.
To see the most recent design details, go to the page "Current Monitor Design Details" under the "PAGES" list.
I plan to update the blog as the design progresses. Hopefully my blogs will improve as I get more comfortable with the process.
