December 15, 2004
HA7NET: Remote Environmental Monitoring on the Cheap
Environmental monitoring is an important aspect of network administration, but it�s always been kind of pricey to do remotely. Most environmental monitoring platforms cost several hundred to several thousand dollars, support only a few expensive, proprietary sensors, and aren�t readily automated through web interactions. As a result, we network administrators tend to monitor one or two environmental variables � temperature, and perhaps humidity � per data center or rack, even though we�d like to measure many more things.
The HA7Net from Embedded Data Systems is a palm-sized Ethernet-equipped Web-enabled environmental monitoring platform that costs only $150.
It supports a huge array of standard off-the-shelf sensors based on the famous Maxim (formerly Dallas Semiconductor) OneWire interface. If you�re not familiar with it, the OneWire interface is a simple single-wire daisy-chain network for slow speed communication with tiny, cheap remote sensing and control devices. These devices include temperature, humidity, and contact closure sensors, remote relays, analog-to-digital and digital-to-analog converters, digital displays, digital key readers, and audible alarms. The operative word here is �cheap.� Unlike competing sensors costing $100 each or more, these typically cost under $20 in single quantities, and you can buy the OneWire components themselves for two or three dollars each and make your own sensors.
Every OneWire device has a unique 64-bit serial number programmed into it, and you can individually address, read, and write to as many as 100 device on the OneWire network through the HA7Net. In OneWire lingo, the HA7Net is a �Bus Master�. But because it�s both Ethernet and Web enabled, it�s an eminently programmable Bus Master that you can easily integrate into your existing network management system.
You interact with the HA7Net using a web browser, over either http or https (SSL) connections. The box has a reasonably friendly Web GUI, but actually manipulating OneWire devices requires a bit of study to understand how the OneWire protocol works. In a nutshell, every OneWire interaction consists of two steps: selecting a device, and then communicating with it. You perform these steps using two HTML transactions, which you can enter manually by hand using any Web browser or automate using a Web scripting engine such as Wget or Lynx.
One of the HA7Net�s HTML commands returns an inventory of all the devices connected to the OneWire network, which lets you quickly verify in a single operation that all your sensors and controls are online and available. You can then communicate with devices individually using additional HTML commands.
Internally the HA7Net sports a multi-user Web server, a battery-backed, SNTP-capable real time clock, a DHCP client, and three-port One-Wire hub that lets you quickly connect off-the-shelf sensors using ordinary modular phone cable. The HA7Net is purely a Web device � it does not support FTP or SNMP -- but it does include telnet terminal access for debugging purposes.
The basic package doesn�t include any sensors, but you can buy plug-and-play units from Embedded Data Systems for $15 or so each, or go right to the source at Maxim and buy raw devices for $2 or $3 each and wire them up yourself. The HA7Net includes a thorough manual that teaches you everything you need to know about OneWire programming, and a number of ready-to-run examples.
In just a few minutes I was able to hook the HA7Net into my Intermapper network management system using a custom script.
Find out more about the HA7Net online at:
http://embeddeddatasystems.com/page/EDS/PROD/HA/HA7Net
You can purchase OneWire devices directly from Maxim at:
http://www.maxim-ic.com/1-Wire.cfm
To find out more about Intermapper, Dr. I. Doctor�s network monitoring tool of choice, visit:
http://www.intermapper.com
Posted by Mel Beckman at December 15, 2004 10:46 AM
