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

2.2.1 Photoelectric Smoke Detector Background – DC-Based Signal Chain

The optical smoke detector, also known as a photoelectric smoke detector, leverages the Mie light-scattering principle to detect the smoke particles rapidly and accurately. Figure 2-2 shows a simplified example of how this detector works. The light-emitting-diode (LED) is pulsed periodically to transmit the light across the detection zone. If there are no smoke particles, minimal light reaches the photosensitive element (photodiode in this case) and hence no smoke alarm is triggered. When there are smoke particles, the pulsed-LED light is scattered to the photodiode (PD) and is translated to an electrical signal with sophisticated front-end circuitry. Once the signal surpasses a certain threshold, the smoke alarm is triggered.

The detection happens in the optical chamber with both optical elements being inside the chamber. The optical chamber serves two goals: (1) the chamber blocks external light from the environment as well as undesired objects such as insects to avoid any false alarm, but allows smoke particles to successfully enter the detection zone, (2) the internal mechanical and material design makes sure that negligible light reaches the photodiode when there is no smoke.

GUID-20231020-SS0I-CNN8-ZJZX-FGPDRSSMDLJK-low.svgFigure 2-2 Detection Principle of Optical Smoke Detector

A conventional optical smoke detector uses a DC-based signal chain that samples the DC signal when the LED is on, but there are some drawbacks to this method. First, the ambient light from the environment acts as an interference signal, which is difficult to distinguish from the actual smoke signal as both are low-frequency signals. However, the optical chamber can be designed to block a majority of the ambient light. Secondly, the DC offset, flicker noise, and input bias current of the transimpedance amplifier (TIA) acts as an error signal for smoke sensing. As illustrated in Figure 2-3, these sources of error limit the signal-to-noise ratio (SNR) of the sensing signal chain.

The aforementioned drawbacks either diminish the performance and robustness or increase the design complexity (better optical chamber) and the cost (better electronics) of the smoke detector.

GUID-20231020-SS0I-R3MR-D1QL-PV1X3MFKRMZ7-low.svgFigure 2-3 DC-Based Smoke Detection Signal Chain