Derivative works — US Patent 5359647

This defensive disclosure document outlines a series of derivative inventions and improvements based on the core principles of US patent 5359647. The purpose of this disclosure is to place these concepts into the public domain, thereby establishing them as prior art for the purposes of patentability examination.

Reference Patent: US 5359647 ("Headset in-use indicator")
Publication Date: April 26, 2026

Series 1: Material & Component Substitutions

1.1. MEMS Microphone with Integrated DSP for Signal Detection

Enabling Description: The discrete analog circuit for audio detection (amplifier, level detector, integrator, comparator) is replaced by a single integrated component: a Micro-Electro-Mechanical Systems (MEMS) microphone with an on-board Digital Signal Processor (DSP). The received audio signal is fed to the MEMS input. The internal DSP is programmed with a firmware algorithm that continuously calculates the Root Mean Square (RMS) power of the signal. If the RMS power exceeds a configurable threshold (e.g., -45 dBFS) for a specified duration (e.g., > 500 milliseconds), a General-Purpose Input/Output (GPIO) pin on the MEMS package is driven to a logic high state. This logic high signal directly gates a P-channel MOSFET, which acts as the switch to apply DC battery voltage to the received audio line for powering the visual indicator. This consolidates the bill of materials, reduces physical footprint, and allows for dynamic, software-based adjustment of detection sensitivity and timing.

Diagram:

flowchart TD
    A[Received Audio Signal] --> B{MEMS Mic w/ DSP};
    B -- RMS Power > Threshold? --> C{GPIO Output High};
    C --> D{MOSFET Switch Closes};
    D --> E[Apply DC Voltage to Audio Line];
    E --> F[Visual Indicator Activated];
    B -- RMS Power <= Threshold --> G{GPIO Output Low};
    G --> H{MOSFET Switch Opens};

1.2. Haptic In-Use Indicator Using Piezoelectric Transducer

Enabling Description: The visual indicator (LED) is replaced with a haptic feedback mechanism to provide a non-visual indication of use. A flat piezoelectric disc transducer is integrated into the headset's earcup housing. The DC voltage applied to the received audio line during an active call does not power an LED, but instead powers a low-current relaxation oscillator circuit (e.g., built with a programmable unijunction transistor). The oscillator output is a square wave tuned to the resonant frequency of the piezoelectric disc (e.g., 250 Hz), causing it to vibrate. The user feels a subtle, continuous hum or a patterned pulse against their ear or temple, confirming an active call state. This is advantageous in tactical environments where light is undesirable or for accessibility applications.

Diagram:

flowchart TD
    subgraph Detection Circuit
        A[Audio Signal] --> B{Detector/Integrator/Comparator};
        B --> C[Activation Signal];
    end
    subgraph Indication Circuit
        D[Battery] -- Switched by C --> E{Relaxation Oscillator};
        E -- 250Hz Square Wave --> F[Piezoelectric Transducer];
        F --> G[Haptic Vibration];
    end

1.3. Fully Flexible Indicator Circuit on Polyimide Substrate

Enabling Description: The entire indicator detection circuit is fabricated as a flexible printed circuit (FPC). A thin, flexible polyimide (e.g., Kapton) or PET substrate is used. Circuit traces, resistors, and capacitor plates are formed using silver nanoparticle conductive ink via screen printing or aerosol jet printing. Surface-mount bare-die versions of the transistors and op-amps are attached using anisotropic conductive adhesive. The entire flexible assembly is then encapsulated in a thin layer of silicone or TPE and laminated directly onto the headset's microphone boom or integrated within the headset cable's outer jacket. This results in a rugged, lightweight, and conformal electronic system that is seamlessly integrated into the headset's physical form.

Diagram:

graph TD
    subgraph Headset Boom Cross-Section
        A(Outer Encapsulation);
        B(Flexible Circuit Layer);
        C(Adhesive Layer);
        D(Boom Structural Core);
    end

    subgraph B - Flexible Circuit Layer
        B1[Printed Silver Traces];
        B2[Embedded Bare-Die Transistor];
        B3[Printed Resistor];
    end

    A --> B;
    B --> C;
    C --> D;

Series 2: Operational Parameter Expansions

2.1. In-Use Indicator for High/Low Temperature Environments

Enabling Description: The invention is adapted for use in extreme temperature environments, from cryogenic (-100°C) to high-heat industrial settings (+150°C). All passive components (resistors, capacitors) are specified with a near-zero temperature coefficient of resistance/capacitance. The active semiconductor components (transistors, comparators) are fabricated from silicon-on-insulator (SOI) or silicon carbide (SiC) wafers for stable operation at temperature extremes. The power source is a specialized lithium-thionyl chloride (Li-SOCl₂) primary cell with a flat discharge curve across a wide temperature range. The entire circuit is potted in a thermally conductive, high-dielectric-strength ceramic-loaded epoxy.

Diagram:

stateDiagram-v2
    [*] --> Idle
    state Operational {
        direction LR
        Idle: Indicator Off
        Active: Indicator On
        Idle --> Active: Audio Detected
        Active --> Idle: Audio Ceases
    }
    note right of Operational
        Operating Range: -100°C to +150°C
        Components: SiC Semiconductors
        Power: Li-SOCl₂ Battery
    end note

2.2. Non-Audible Frequency Carrier Detection

Enabling Description: The indicator activates based on the presence of a non-audible supervisory tone or digital carrier signal, rather than voice audio. The front-end amplifier is replaced with a high-Q band-pass filter centered on a specific carrier frequency (e.g., 38 kHz). The filter's output is fed into a phase-locked loop (PLL) circuit. When the 38 kHz carrier is present on the received audio line (indicating the communication channel is open, even if silent), the PLL achieves a "locked" state. The lock-detect output pin of the PLL serves as the activation signal for the switch, powering the visual indicator. This provides a highly reliable indication of an "on-line" condition, immune to false positives from ambient or crosstalk noise.

Diagram:

flowchart TD
    A[Received Signal (Audio + 38kHz Carrier)] --> B[Band-Pass Filter @ 38kHz];
    B --> C[Phase-Locked Loop (PLL)];
    C -- Lock Detected? --> D{Activation Signal High};
    D --> E[Indicator ON];
    C -- No Lock --> F{Activation Signal Low};
    F --> G[Indicator OFF];

Series 3: Cross-Domain Applications

3.1. Aerospace: Sterile Cockpit Communication Monitor

Enabling Description: The audio detection mechanism is applied to monitor aircraft cockpit intercom channels to enforce "sterile cockpit" rules below 10,000 feet. The system taps into the CVR/intercom audio lines and is enabled by a discrete signal from the air data computer indicating altitude is below 10,000 feet. The audio detector is tuned to the frequency range of human speech and the integrator time constant is set to 15 seconds. If non-essential conversation (continuous speech exceeding 15 seconds) is detected, a non-critical amber annunciator light illuminates on the flight panel, providing a silent, non-disruptive reminder to the crew to limit communication to essential flight matters.

Diagram:

sequenceDiagram
    participant ADC as Air Data Computer
    participant Monitor as Sterile Cockpit Monitor
    participant Panel as Annunciator Panel
    participant Intercom
    ADC->>Monitor: Altitude < 10,000 ft (Enable)
    Intercom->>Monitor: Continuous Speech Audio (>15s)
    Monitor->>Panel: Activate Amber Light
    Intercom->>Monitor: Speech Ceases
    Monitor->>Panel: Deactivate Light
    ADC->>Monitor: Altitude > 10,000 ft (Disable)

3.2. AgTech: Bovine Distress Vocalization Alerter

Enabling Description: A ruggedized, solar-powered audio monitoring device is attached to a livestock ear tag. The detection circuit employs a DSP programmed with a machine learning model (e.g., a lightweight convolutional neural network) trained to recognize the specific acoustic signatures of bovine distress vocalizations. When a vocalization pattern is positively identified with a confidence score above 95%, the DSP generates an activation signal. This signal powers up a LoRaWAN radio module, which transmits a small alert packet containing the animal's ID and the event type to a central base station on the farm. The system remains in a deep sleep state, drawing microamps, until activated by the specific audio signature.

Diagram:

stateDiagram-v2
    [*] --> Listening
    Listening --> Analyzing: Potential Vocalization Detected
    Analyzing --> Listening: (Noise/False Positive)
    Analyzing --> Transmitting: Distress Signature Confirmed (ML Model)
    Transmitting --> Listening: (Alert Sent via LoRaWAN)

3.3. Consumer Electronics: Smart Speaker Active Listening Indicator

Enabling Description: A standalone hardware device provides a verifiable, out-of-band privacy indication for smart speakers. The device uses a near-field inductive probe to non-invasively detect the specific high-frequency electronic noise (e.g., from the clock of the ADC) that is only present when the smart speaker's microphone array is active and digitizing audio for streaming. This signal is amplified, filtered, and then processed by the detector/integrator circuit. When the electronic signature is present for more than one second, the comparator triggers a bright, wide-angle red LED. This provides a physical, tamper-evident guarantee of the device's listening state, independent of any software-controlled indicator light on the speaker itself.

Diagram:

flowchart TD
    A[Smart Speaker Internals] -- Radiates Electronic Noise --> B(Inductive Probe);
    B --> C[Amplifier & High-Pass Filter];
    C --> D{Noise Signature Detector};
    D -- Signature Present? --> E[Activate Red Privacy LED];
    D -- Signature Absent? --> F[Deactivate LED];

Series 4: Integration with Emerging Technologies

4.1. AI-Driven Contextual Call Indicator

Enabling Description: The indicator's behavior is dynamically modulated by an edge AI processor integrated into the headset. An ARM Cortex-M microcontroller with an NPU continuously analyzes the received audio stream. A compact neural network performs real-time keyword spotting, sentiment analysis, and speaker identification. The indicator is a multi-color RGB LED. Based on the AI's analysis, the output is contextual: solid blue for normal conversation; slow-pulsing green when a manager's voice is detected; fast-pulsing red if the caller's sentiment is classified as "angry" or "distressed"; and a yellow "breathing" effect when keywords like "urgent" or "deadline" are spotted. This provides the user with at-a-glance contextual information about the call's nature.

Diagram:

graph TD
    A[Audio Stream] --> B{Edge AI Processor};
    B -- Analysis --> C{Indicator Logic};
    C -- Normal Sentiment --> D[Set RGB LED to Blue];
    C -- Negative Sentiment --> E[Set RGB LED to Pulse Red];
    C -- Keyword 'Urgent' --> F[Set RGB LED to Yellow];
    C -- Manager Voice ID --> G[Set RGB LED to Pulse Green];

4.2. IoT-Enabled Presence and Status Synchronization

Enabling Description: The headset's in-use activation signal simultaneously triggers a Bluetooth Low Energy (BLE) module within the headset. The BLE module broadcasts a standardized presence service GATT profile, changing a characteristic's value from "Available" to "In-Call". A nearby IoT gateway (e.g., a desk phone, computer, or dedicated hub) subscribes to this characteristic. Upon detecting the change, the gateway pushes a status update via MQTT to a cloud service. This service uses APIs to automatically update the user's presence in collaboration platforms like Microsoft Teams, Slack, and Cisco Webex to "Busy - On a call," and can trigger smart office routines like activating a "Do Not Disturb" light at the user's desk.

Diagram:

sequenceDiagram
    participant Headset
    participant Gateway as IoT Gateway
    participant Cloud
    participant UC_Platform as Collaboration Platform

    Headset->>Headset: Call Active, Activation Signal High
    Headset->>Gateway: BLE GATT Update (Status: In-Call)
    Gateway->>Cloud: MQTT Publish (user: X, status: InCall)
    Cloud->>UC_Platform: API Call (Update Presence)
    UC_Platform-->>UC_Platform: User status is now "Busy"

Series 5: Inverse and Failure Mode Disclosures

5.1. Fail-Safe "Heartbeat" Indicator

Enabling Description: The indicator logic is inverted to provide a clear signal of both system health and in-use status. In the idle state (on-hook), a low-power timer circuit causes the indicator LED to emit a slow, brief "heartbeat" flash (e.g., 50ms every 5 seconds). This confirms the indicator circuit has power and is operational. When a call is detected, the comparator's output signal disables the heartbeat timer and turns the LED to a solid ON state. If the battery dies or the circuit fails, the LED is permanently OFF. This creates three unambiguous states: Slow Pulse = Ready; Solid On = In-Use; Off = System Fault/No Power.

Diagram:

stateDiagram-v2
    [*] --> Ready
    state Ready: LED Slow Pulse (Heartbeat)
    state In_Use: LED Solid On
    Ready --> In_Use: Audio Detected
    In_Use --> Ready: Audio Ceases
    Ready --> Fault: Battery/Circuit Failure
    In_Use --> Fault: Battery/Circuit Failure
    state Fault: LED Off

Combination Prior Art with Open-Source Standards

1. WebRTC and WebHID Integration

Enabling Description: The in-use indication is controlled by an open web standard rather than analog audio detection. The headset connects to a computer via USB and exposes a Human Interface Device (HID) endpoint. A web application using the WebRTC API for a call, also uses the WebHID API to gain access to the headset. When the RTCPeerConnection state transitions to connected, the JavaScript application sends a specific HID output report to the headset. The headset's firmware interprets this report as the "activation signal" and powers the indicator LED. When the call ends (disconnected state), a different HID report is sent to turn the light off. This creates a hardware in-use indicator for browser-based communications controlled entirely by open W3C standards.

2. FreeRTOS-Based Software-Defined Detector

Enabling Description: The patent's detection logic is implemented entirely in software on a microcontroller running the open-source FreeRTOS. The received audio line is connected to the microcontroller's ADC. A high-priority FreeRTOS task continuously samples the audio. The samples are processed using a software-based DSP library (e.g., CMSIS-DSP) to perform filtering and RMS power calculation, emulating the amplifier and detector. The result is passed to a second task which implements a digital IIR filter, emulating the integrator. This task compares the output to a configurable threshold and, if exceeded, uses a FreeRTOS semaphore to signal a third task, which manages the GPIO pin connected to the indicator LED, allowing for complex patterns like fades and programmable flash rates.

3. SIP-Triggered VoIP Indicator

Enabling Description: The indicator is triggered by passively monitoring network traffic for Session Initiation Protocol (SIP) messages, an open IETF standard (RFC 3261). A small network device (e.g., running OpenWrt) is configured to mirror the traffic of a VoIP phone. A process on the device uses libpcap to capture packets and specifically filters for SIP messages. Upon seeing a "200 OK" response to an "INVITE" request for the monitored extension, the device sends an activation signal (e.g., via a USB-to-GPIO adapter) to an external indicator circuit. The indicator is deactivated upon the capture of a "BYE" message. This provides an extremely reliable in-use status for VoIP systems that is independent of audio levels or encryption.