November 2005, Issue 184

Water Pressure Sensor
ZigBee-Based NozzleMon Aids Firefighters

SYSTEM OVERVIEW

In the NozzleMon system, a Freescale ZigBee family evaluation board, the 13192-EVB, serves as the controller in the pump panel unit (PPU) to receive and display the nozzle’s data. An MC13192 sensor application reference design (SARD) board serves as the nozzle unit (NU) processor that manages the sensors near the nozzle.

Pressure sensing is performed by an MPXH6400A integrated silicon pressure sensor, which I used to replace the MPXM2010GS on the breakaway board from the 2004 Freescale Wireless Design Challenge. Position sensing is achieved with the x- and y-axis (MMA6261Q) and z-axis (MMA1260D) accelerometers on the SARD board. Even after substituting the MPXH6400A for the MPXM201GS, a mechanical transducer was required to scale down the pressure and isolate the water from the transducer.

The PPU includes a 2 × 24 LCD for displaying pressure readings and messages. It also has an ultra-bright red LED for indicating problems, a large push button for indicating a set pressure (SP), and a toggle switch for turning on the power.

The PPU continuously polls the nozzle for data, updating its displays with every successful reception. The LCD normally displays the latest (instantaneous) pressure reading on the first line and the average of the previous 16 readings on the second line. If the red button is pressed, the current average pressure becomes the set pressure. If the average pressure is more than 10 psi above or below the set pressure, a “Pressure out of range” message appears on the first line of the LCD and the red LED illuminates. These error indications will remain until the average returns to the set pressure range or the red button is pressed again to clear the set pressure.

Other messages that may appear on the first line include “No signal from nozzle!” and “Nozzle out of control!” Each message is also accompanied by the illumination of the red LED. The NozzleMon doesn’t have audible output because the environments that pump operators find themselves in are usually noisy.