TIDUF52 December   2023 MSPM0L1303 , MSPM0L1304 , MSPM0L1305 , MSPM0L1306 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Photoelectric Smoke Detector Background – DC-Based Signal Chain
      2. 2.2.2 Modulation-Based Smoke Detection Signal Chain
      3. 2.2.3 Optical Sensing AFE Design
        1. 2.2.3.1 TIA
        2. 2.2.3.2 BPF
        3. 2.2.3.3 Demodulator and Integrator
        4. 2.2.3.4 LED Driver
      4. 2.2.4 Optical and Mechanical Design
    3. 2.3 Highlighted Products
      1. 2.3.1 MSPM0L1306
      2. 2.3.2 TLV9062S
      3. 2.3.3 TPS7A24
      4. 2.3.4 TS5A623157
      5. 2.3.5 SN74LVC1G66
      6. 2.3.6 HDC2010
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Power
      2. 3.1.2 Communication Interface
      3. 3.1.3 Headers
    2. 3.2 Software Requirements
      1. 3.2.1 Getting Started Firmware
      2. 3.2.2 Measurements and Smoke Detection
      3. 3.2.3 Additional Demonstration Functionality
      4. 3.2.4 Smoke Detector GUI
    3. 3.3 Test Setup
      1. 3.3.1 UL217 Smoke Box and Fire Testing Setup
      2. 3.3.2 Ambient Light Testing Setup
      3. 3.3.3 Air-Quality Sensing Test Setup
    4. 3.4 Test Results
      1. 3.4.1 UL217 Testing Results
      2. 3.4.2 Ambient Light Testing Results
      3. 3.4.3 Air-Quality Sensing Test Results
      4. 3.4.4 Power Testing Results
      5. 3.4.5 Fire Room Smoke Testing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 CAD Files
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.2 Modulation-Based Smoke Detection Signal Chain

This design adopted a modulation-based smoke sensing signal chain to overcome the limitations of the DC-based signal chain. As shown in Figure 2-4, the smoke signal is modulated to frequency fmod by sending a series of LED pulses at the frequency of fmod. The frequency, fmod, is selected to be far from the frequency of different types of ambient lights; for example, the LED and incandescent light interference located around 120 Hz along with harmonics of the 120-Hz fundamental frequency, and florescent light interference located around 44 kHz along with harmonics of the 44-kHz fundamental frequency. The modulated signal with ambient light interference is filtered by a bandpass filter with a center frequency located at fmod. The interference is attenuated by the bandpass filter while the smoke signal is retained. The signal is then demodulated back into baseband while the low-frequency interference is modulated up to fmod. With additional low-pass filtering, the interference is attenuated again, yielding an interference-free smoke signal around DC at the baseband. The demodulated signal is sampled by an Analog-to-Digital Converter (ADC) and stored for further post-processing. The modulation, demodulation, filtering and sampling is operated pulse by pulse. Better SNR can be achieved by sending a higher number of pulses (stronger filtering, more averaging, and lower noise) at the cost of power consumption.

GUID-20231020-SS0I-Z163-5L5H-CHT8ZFPSPJSR-low.svgFigure 2-4 Modulation-Based Smoke Detector Signal Chain