Glass Break Detector
Design
Considerations
Glass Break Detector can be designed with 3 types of implementations in mind: Standalone, wireless connectivity and Fixed/Wired Connectivity. The first two implementations are battery operated. The functional block diagram of the glass break detector is divided into 3 sub-blocks: the sensing block, the processor and the communication interface blocks. When implementing a basic standalone type of glass break detector, the processor and the communication interface are not needed. The sensing block is comprised of an acoustic device (Microphone) to sense the specific high frequency tinkle of shattered glass, and two operational amplifiers to amplify the detected frequency and enable the ADC in the MSP430 to sample the signal. With the need of extended battery life for standalone and wireless connectivity implementations, MSP430 microcontrollers with their low current consumption are ideal fit for these applications.
It is important to balance cost vs. settling-time performance, while minimizing current consumption when selecting an external operational amplifier for the application. Settling time is important in allowing the detector to provide multiple reports of a glass break event in a short period of time, so as to minimize any false alarms. To further reduce current consumption of external components, some may be powered directly from an MSP430 port pin. This will take the current consumption of the amplifier to zero, when the MSP430 is in a standby state, significantly increasing the battery run time of this application.
Communications Interfaces
RF Transceiver: Range, network configuration and power consumption are important factors when selecting a Low Power Wireless (LPW) solution. Range is affected by output power, sensitivity and selectivity, which in turn impact the jamming of other signal sources and the ability to distinguish the desired signal from local interferers. Selectivity is also important in RF design, especially when designing products in the 2.4GHz band, where interference from other equipment is likely. When making the RF radio selection, it is also important to understand the network configuration is which the glass break detector will be use: Point to Point, Star or Mesh Network, as it may impacted the radio, processor, memory and power requirements of the system.
Line Powered: Power over Ethernet (IEEE 802.3af) integrates data and power over standard LAN connection. It provides uninterrupted 15W max (13W load), 48V nominal supply to the devices connected to the system. The power requirement for glass break detectors is well below the ~ 12.5W limit for powered devices and can be easily powered from PoE. This sort of implementation removes the need to run AC power to sensor locations, and reduces the cost of the power supply in the detector by requiring only DC/DC power conversion.
Glass Break Detector can be designed with 3 types of implementations in mind: Standalone, wireless connectivity and Fixed/Wired Connectivity. The first two implementations are battery operated. The functional block diagram of the glass break detector is divided into 3 sub-blocks: the sensing block, the processor and the communication interface blocks. When implementing a basic standalone type of glass break detector, the processor and the communication interface are not needed. The sensing block is comprised of an acoustic device (Microphone) to sense the specific high frequency tinkle of shattered glass, and two operational amplifiers to amplify the detected frequency and enable the ADC in the MSP430 to sample the signal. With the need of extended battery life for standalone and wireless connectivity implementations, MSP430 microcontrollers with their low current consumption are ideal fit for these applications.
It is important to balance cost vs. settling-time performance, while minimizing current consumption when selecting an external operational amplifier for the application. Settling time is important in allowing the detector to provide multiple reports of a glass break event in a short period of time, so as to minimize any false alarms. To further reduce current consumption of external components, some may be powered directly from an MSP430 port pin. This will take the current consumption of the amplifier to zero, when the MSP430 is in a standby state, significantly increasing the battery run time of this application.
Communications Interfaces
RF Transceiver: Range, network configuration and power consumption are important factors when selecting a Low Power Wireless (LPW) solution. Range is affected by output power, sensitivity and selectivity, which in turn impact the jamming of other signal sources and the ability to distinguish the desired signal from local interferers. Selectivity is also important in RF design, especially when designing products in the 2.4GHz band, where interference from other equipment is likely. When making the RF radio selection, it is also important to understand the network configuration is which the glass break detector will be use: Point to Point, Star or Mesh Network, as it may impacted the radio, processor, memory and power requirements of the system.
Line Powered: Power over Ethernet (IEEE 802.3af) integrates data and power over standard LAN connection. It provides uninterrupted 15W max (13W load), 48V nominal supply to the devices connected to the system. The power requirement for glass break detectors is well below the ~ 12.5W limit for powered devices and can be easily powered from PoE. This sort of implementation removes the need to run AC power to sensor locations, and reduces the cost of the power supply in the detector by requiring only DC/DC power conversion.
