January 2006, Issue 186

Electronic Scarecrow

CONSTRUCTION

Photo 2 shows the Freescale ZigBee demonstration boards and all of the sensors from the sensor breakaway board supplied to ZigBee Wireless Design Challenge entrants. The SARD boards I used for the remote units required significant modification. Most of the sensor boards were fairly easy to modify because almost all of the IC pins were in just the right places to install connectors where I needed them. The notable exception was the MMA6261Q accelerometer, which was missing a connection on its self-test pin. Its pins are underneath the package, so it was a challenge.

I mounted the photovoltaic cells on a curved piece of plastic and attached it to the top of a heavy-duty garden stake (see Photo 1). The cells are rated for short-term outdoor use, so I’ll add a protective layer on top of them at some point. The box mounts on the same stake so its built-in accelerometer can pick up movement. The two RJ-11 jacks located just above the batteries are for a second accelerometer and the pressure sensor, which are both mounted in tiny boxes and can be placed in other areas of my property.

The base unit’s evaluation board was much easier to modify (see Photo 3). I replaced the power supply, added circuitry for the X10 interface, and moved some connectors so the board would fit into the box. I mounted the push buttons on a small piece of perf board that I attached to the LCD.

I sandwiched together the LCD and evaluation boards before dropping them into the plastic box. I made the front panel legend by running an adhesive Mylar sheet through a laser printer.

I wanted to be able to carry the base unit outside, so I made a portable power source by putting the PCB containing a 9-V battery and 5-V regulator from the breakaway board in a small box.