SLAA351A April   2007  – November 2018 MSP430F2232 , MSP430F2232 , MSP430F2234 , MSP430F2234 , MSP430F2252 , MSP430F2252 , MSP430F2254 , MSP430F2254 , MSP430F2272 , MSP430F2272 , MSP430F2274 , MSP430F2274

 

  1.   A Simple Glass-Breakage Detector Using an MSP430™ MCU
    1.     Trademarks
    2. 1 Introduction
    3. 2 Hardware Description
      1. 2.1 Device Specifications
      2. 2.2 Power Supply
      3. 2.3 Microphone
      4. 2.4 LED and Buzzer Alert
      5. 2.5 Interface to CC1100 or CC2500 Devices
      6. 2.6 Operational Amplifiers (OAs)
      7. 2.7 Internal Very-Low-Power Oscillator (VLO)
      8. 2.8 JTAG Interface
      9. 2.9 Current Consumption
    4. 3 Software Description
      1. 3.1 Initialization Routine
      2. 3.2 Timer_A
      3. 3.3 ADC10
      4. 3.4 Signal Analysis
        1. 3.4.1 First Stage of Processing
          1. 3.4.1.1 Signal Averaging, Peak Detection, and Zero Crossings
          2. 3.4.1.2 High-Pass Filtering
        2. 3.4.2 Second Stage of Processing
          1. 3.4.2.1 Frequency Composition Ratio
          2. 3.4.2.2 Peak and Zero-Crossing Count
          3. 3.4.2.3 Glass-Breakage Detect
    5. 4 Hardware Schematic
    6. 5 Test Setup
    7. 6 References
  2.   Revision History

2.7 Internal Very-Low-Power Oscillator (VLO)

The MSP430F2274 has an internal VLO that typically operates at 12 kHz. With the VLO as a clock source, the MSP430 MCU can be operated in low-power mode 3 (LPM3). Using the VLO eliminates the need for an external low-frequency crystal. The VLO is the clock source to the internal timer, which is functional when the device is in standby or LPM3. Timer_A is responsible for the periodic wake up every 2 ms. Due to the temperature drift of the VLO frequency, this wake-up time could be different. An algorithm to consider the drift of the VLO and its impact on the wake up time of 2 ms is not implemented but can be added. For example, the factory-provided DCO calibration constants in the flash memory can be used to determine the VLO frequency and adjust the length of the wake-up interval accordingly.