Deaf-Guardian

Deaf-Guardian: Reducing the gap between sound and silence with real-time multi-modal AI.

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Inspiration

For individuals who are deaf or hard of hearing, missing critical environmental sound cues—such as doorbells, smoke alarms, or emergency signals—can pose serious safety hazards and daily challenges.

Deaf-Guardian was born out of the vision to create an open-source, affordable, and modular Raspberry Pi HAT that bridges this accessibility gap. By integrating real-time I2S digital sound sensing with dual physical feedback mechanisms (high-torque haptic vibration and high-intensity RGB strobe light alerts), the device senses environmental acoustic events and instantly translates them into touch and visual warnings.

How I Built The Project

The project was designed as a modular Raspberry Pi HAT featuring four core hardware sub-systems. I utilized EasyEDA for the schematic capture and PCB layout.

+------------------+      I2S Audio Data     +-------------------+
| INMP441 MEMS Mic | ---------------------> |   Raspberry Pi    |
+------------------+                        | (Signal Analytics)|
                                            +---------+---------+
                                                      |
                       +------------------------------+------------------------------+
                       | GPIO Trigger                                                | GPIO Signal (PWM)
                       v                                                             v
            +--------------------+                                        +--------------------+
            | AO3400A N-MOSFET   |                                        | WS2812B RGB Strip  |
            | Haptic Driver      |                                        | Visual Alert       |
            +---------+----------+                                        +--------------------+
                      |
                      v
            +--------------------+
            | Vibration Motor    |
            +--------------------+

1. Digital Audio Sensing (INMP441 MEMS Microphone)

  • Digital Transmission: Interfaced via I2S protocol (I2S_SCK, I2S_WS, and I2S_SD) connected directly to the Raspberry Pi 40-pin header.
  • Power Stability: Filtered using parallel 0.1uF ceramic and 10uF tantalum decoupling capacitors on the +3.3V rail.
  • Channel Definition: Configured with a 100k Ohm pull-down resistor on the SD line to ensure stable data transmission.

2. Haptic Vibration Motor Driver

Since Raspberry Pi GPIO pins cannot directly drive high-current inductive motors:

  • Switching Element: Utilized an AO3400A N-Channel MOSFET.
  • Flyback Protection: Placed a fast 1N4148W freewheeling diode in anti-parallel across the motor 2P header to safely clamp inductive back-EMF voltage spikes when turned off:

$$V_{kickback} = -L \frac{di}{dt}$$

  • Gate Damping: Integrated a 100 Ohm series gate resistor alongside a 10k Ohm pull-down resistor to eliminate floating gate logic during startup.

3. Visual Strobe Alert Interface (WS2812B RGB LED)

  • Header Connection: 3P 2.54mm male header supplying +5V, GND, and DIN.
  • Transient Voltage Buffer: High-brightness white strobe flashes create rapid current surges. A bulk 100uF reservoir capacitor paired with a 100nF ceramic capacitor was connected across the +5V rail to absorb transient spikes and prevent system reboot.
  • Signal Integrity: A 330 Ohm series damping resistor was added on the DIN trace to eliminate signal ringing and reflections.

4. Mute & Emergency Interface

  • Integrated a tactile button connected between GPIO_BTN and GND, allowing immediate alarm muting or manual SOS triggering via software pull-up configuration.

Challenges I Faced

  • System Power Voltage Dips During Strobe Flashes
    • Issue: Simultaneously flashing full-brightness RGB LEDs produced sharp current spikes, causing the system +5V rail to dip and triggering Raspberry Pi under-voltage warnings.
    • Solution: Placed a 100uF electrolytic capacitor directly adjacent to the 3P LED connector to act as a localized energy buffer.
  • Inductive Noise from the Vibration Motor
    • Issue: Switching the DC motor on and off created high-voltage back-EMF kickbacks that risked damaging the switching MOSFET.
    • Solution: Incorporated a 1N4148W flyback diode across the motor terminals to safely recirculate and dissipate inductive coil current.

What I Learned

Through designing and engineering the Deaf-Guardian HAT, I gained significant practical knowledge in:

  • Hardware & Circuit Design: Schematic capture and component layout using EasyEDA and LCSC component libraries.
  • High-Speed Digital Interfaces: Routing I2S audio lines and ensuring noise immunity in audio sensing circuits.
  • Power Distribution Networks (PDN): Managing transient power demands for high-current loads (motors and LED arrays).
  • DRC & Manufacturing Readiness: Executing complete Design Rule Checks (DRC) to verify net consistency and prepare files for PCB fabrication.

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