Repository: voice-feedback-device-documentation
This section documents the firmware implementation for the first-generation voice feedback device, as maintained in the project GitHub repository.
- TinyGSM – LTE modem communication
- SPI – Peripheral communication interface
- SD – Local SD card storage
- TMRPCM – Audio recording and playback in WAV format
- EEPROM – Persistent storage of counters and device state
- ARDUINO-TIMER – Task scheduling and low-power timing
- Device remains in low-power sleep mode by default
- User presses button → device wakes up
- Records a voice feedback audio file (
.wav) - Stores file on SD card
- Increments file counter
- When 5 files are recorded:
- LTE modem activates
- All 5 files are uploaded to the citizen feedback portal
- Counter resets to 1
- Device returns to sleep mode
This document summarizes the evolution of the Sema Audio Feedback Devices across four major iterations. It highlights the hardware choices, functional improvements, power performance, and deployment considerations to support decision‑making on which device version is best suited for specific field deployments.
To provide a clear comparison of Sema device versions developed over time, showing technological progress, feature improvements, and deployment trade‑offs for supervisors and project stakeholders.
Purpose: First proof‑of‑concept for collecting citizen audio feedback and transmitting to the portal.
Key Features
- Main controller: Arduino Mega Pro Mini
- Audio format: WAV recording
- Transmission: LTE modem upload to citizen feedback portal
- Maximum audio length: 15 seconds
- Power: 2 lithium batteries (series or parallel configuration)
- Runtime: ~2 days
- Audio quality: Raw microphone input, no background noise suppression
Pros
- Functional end‑to‑end audio capture and upload
- Simple and low-cost design
Cons
- Short battery life
- Limited recording duration
- No noise suppression
Purpose: Improved upon v1.0 with longer recording and better audio clarity.
Key Features
- Main controller: Arduino Mega Pro Mini
- Audio format: WAV recording
- Transmission: LTE modem upload to citizen feedback portal
- Maximum audio length: Up to 1 minute (can stop early when user finishes)
- Microphone: Noise‑cancellation microphone
- Power: 3 lithium batteries in series
- Runtime: ~7 days
- Audio quality: Improved with background noise suppression
Pros
- Better audio clarity
- Longer battery life
- Longer flexible recording duration
Cons
- Increased power complexity
- Still dependent on LTE connectivity
 |
 |
| Version 1.2.1 | Version 1.2.2 |
Purpose: Designed for deployments without continuous internet connectivity.
Key Features
- Main controller: Arduino Nano
- Audio format: WAV recording
- Transmission: No cloud upload; files stored locally
- Maximum audio length: Up to 1 minute (early stop supported)
- Microphone: Noise‑cancellation microphone
- Power: 3 lithium batteries in series
- Runtime: ~14 days
Pros
- Longest battery life among Arduino-based versions
- Does not require network connectivity
- High audio quality
Cons
- Requires manual retrieval of stored audio files
- No real‑time monitoring
Purpose: Transition to embedded Linux for advanced processing and connectivity.
Key Features
- Main controller: Raspberry Pi Zero 2W
- Audio input: USB microphone
- Transmission: Raspberry Pi 4G HAT with USB attachment
- Audio handling: On‑device recording and processing
- Runtime: ~4 hours
Pros
- Supports advanced processing and future ML integration
- Flexible software environment
- Direct cloud connectivity
Cons
- Short battery life
- Higher power consumption
- Increased system complexity
| Feature | Version 1.0 | Version 1.2 | Version 2 | Version 3 |
|---|---|---|---|---|
| Main Controller | Arduino Mega Pro Mini | Arduino Mega Pro Mini | Arduino Nano | Raspberry Pi Zero 2W |
| Audio Format | WAV | WAV | WAV | WAV |
| Max Recording Length | 15 sec | 1 min | 1 min | Configurable |
| Audio Upload | LTE to portal | LTE to portal | Local storage only | 4G Cloud upload |
| Microphone | Standard | Noise‑cancellation | Noise‑cancellation | USB Microphone |
| Noise Suppression | No | Yes | Yes | Depends on software |
| Power Source | 2 Li batteries | 3 Li batteries | 3 Li batteries | Li battery pack |
| Runtime | ~2 days | ~7 days | ~14 days | ~4 hours |
| Connectivity Requirement | LTE | LTE | None | 4G |
| Deployment Mode | Online | Online | Offline | Online / Smart IoT |
Short-term citizen feedback pilots (connected areas):
- Version 1.2 – Reliable connectivity and good audio quality
Remote or off-grid deployments:
- Version 2 – Long battery life and offline storage
Advanced sensing and real-time monitoring:
- Version 3 – Supports future ML, dashboards, and OTA updates
- Progressive improvement in battery efficiency
- Introduction of noise‑cancellation microphones
- Transition from microcontroller to embedded Linux
- Shift from short recordings to flexible user-controlled recordings
- Gradual integration toward smart connected sensing platforms
- Power optimization for Raspberry Pi platform
- Hybrid online/offline synchronization
- On-device speech-to-text or classification
- Solar-assisted charging
You can view the circuit schematics for each device version below:
The Sema Audio Feedback Devices support flexible power input for both grid-connected and off-grid deployments.
- Series configuration: 12.6V DC charging (12V adapter or solar)
- Parallel configuration: 5V DC charging (low-power systems)
The PCB includes an on-board buck-boost converter that:
- Accepts solar panels or DC adapters (up to 20V max input)
- Automatically regulates voltage for battery charging and device operation
- Enables direct solar panel connection without external regulation
- Mains: 12V DC adapter
- Solar: Panel (≤20V) via onboard regulator
- Battery: Internal lithium pack
| SN | Item Name | Description | Qty | Unit Cost (UGX) | Total Cost (UGX) |
|---|---|---|---|---|---|
| 1 | Lithium batteries | 2600mAh | 3 | 5,000 | 15,000 |
| 2 | Microcontroller | Mega Pro Mini | 1 | 80,000 | 80,000 |
| 3 | 4G Modem (inbuilt GPS) | SIM7600 | 1 | 140,000 | 140,000 |
| 4 | Lithium charger | 3S charger | 1 | 20,000 | 20,000 |
| 5 | Recording module | MAX9814 | 1 | 20,000 | 20,000 |
| 6 | SD card reader | Read SD card | 1 | 10,000 | 10,000 |
| 7 | SD card | 1GB | 1 | 15,000 | 15,000 |
| 8 | Switch | Power device on or off | 1 | 3,000 | 3,000 |
| 9 | RTC | DS3231 | 1 | 12,000 | 12,000 |
| 10 | Voltage step-down 1 | Circuit step-down | 1 | 20,000 | 20,000 |
| 11 | Switching transistor | TIP122 | 1 | 1,500 | 1,500 |
| 12 | Switching resistor | 1K Ohm | 2 | 500 | 1,000 |
| 13 | Power block diodes | 2N1001 | 2 | 1,000 | 2,000 |
| 14 | Header pins | Component slot | 1 | 5,000 | 5,000 |
| 15 | Glue stick | Assembly | 1 | 5,000 | 5,000 |
| 16 | RTC battery | RTC power | 1 | 3,000 | 3,000 |
| 17 | PCB | PCB board | 1 | 30,000 | 30,000 |
| Total (UGX) | 382,500 | ||||
| Total (USD) | ~103.21 |
Supplier: Bbiri Centre
Author: Joel T. Muhanguzi
Project: Sema Audio Feedback Hardware Evolution