October's feature

River depth to the Web.

A friend near a river has need of minding our west-of-Boston flooding. I am helping him out with a little exercise in off-the-shelf integration.

The purveyors at Omega offer wireless sensor pairs that use IEEE's 802.15.4 standard, with receiver units that have hardware-based web servers. Hard to beat!

Add a differential pressure sensor, some tubing, a fish-tank pump, and away we go.

Status: Testing.

Previous features.

Receiver unit, or, as they call it, a "coordinator." Talks 802.15.4 to the sensor unit at the other end. Talks TCP/IP to the 'Net; it has a Web server built right in.

The "End Device" talks 802.15.4 to the "Coordinator," and uses that protocol to send occasional (configurable!) bursts of sensor readings that it has digitized from analog signals from one or two sensors. Runs for months and months on two D-Cells.

In this picture, you can see a little four-pin device. That's a Honeywell differential pressure sensor. In this installation, one side is open to the atmosphere, the other side is connected to a tube that runs from the relative safety of a small structure near the river (in the floodplane, nonetheless) down into the river, where the other end sits, open to the water, at the bottom.

Up near the sensor is a little aquarium pump... it pushes air through a t-fitting in the tube mentioned above every hour or so to keep out the crud. (Observant kayakers might notice a tiny trickle of bubbles at the river's surface if their timing is right.)

The pressure in the tube, then is the pressure at the bottom of the river, minus ambient pressure.

So far in tank tests here in the house, it measures depth to within a fraction of an inch repeatably. Can't wait to test it in the river itself!

Past features. - Back.