Start • System Overview • Installation & Operation • Garage Door Module • Water Level Module • Temperature Module • Hardware Design • Garage Door Sensor • Water Level Sensor • Temperature Sensor • Software Design • Improvements • Peace of Mind • Sources and PDF

GARAGE DOOR SENSOR

I started the remote sensor design with the garage door module because all of the required hardware was already part of the MC13192-SARD PCB, with one minor exception I will discuss later. With the high level of hardware integration on the MC13192-SARD, the design of this sensor was software only, but this provided an easy starting point to start software development and quickly implement a sensor for the validation of the base unit’s reception abilities.

The garage door module uses the Freescale MMA1260D 1.5-g z-axis accelerometer included on the MC13192-SARD PCB to detect the position of the garage door. The MC13192-SARD periodically wakes up, checks the accelerometer, and sends an error code when –1 g (due to the force of gravity) is seen. The PCB must be mounted on the garage door with the solder side toward the door so that it is horizontal and upside down on the raised garage door.

The minor exception I mentioned earlier is power management. One of the great things about the 802.15.4 wireless networking standard and the protocols that build on it (e.g., Freescale’s Simple MAC and Zigbee) is low-power consumption. Units can sleep the majority of the time and thereby reduce the average power. Unfortunately, with the hardware provided for the Wireless Design Challenge, there was no way to put the accelerometers or serial port chip on the MC13192-SARD board into Power Down mode, so I couldn’t implement a low-power Sleep mode. With a custom PCB, I could have included power control for these components as well.