BlueBark Lite

A lightweight Raspberry Pi + RTL-SDR signal presence detector for TETRA-like RF activity (Emergency Vehicles Detector).

What It Does

• Scans the configured RF bands with rtl_power_fftw.
• Keeps the strongest unread sweep in the Cython bridge so short bursts are not overwritten before Python sees them.
• Drives a small OLED meter and status readout.
• Uses three membrane buttons for mute, mode, squelch floor, shutdown, and OLED rotation.
• Beeps through an active buzzer when signal thresholds are crossed.
• Basically it's an emergency services alert system

OLED Layout

The OLED is intentionally minimal so it stays readable at a glance.

• Left side: a 13-step vertical signal bar that grows with detected energy.
• Peak marks: small dots that hold the strongest recent level for a short time.
• Right side: a mode letter, the current squelch floor, a mute icon when muted, and the peak dB text.
• Temporary overlay: CPU temperature replaces the bar briefly after a short press on the shutdown button.
• Alarm bloom: the upper signal bar brightens when the alarm threshold is reached.

Project Layout

• bluebark_lite_app.py: main application, OLED UI, button handling, SDR restart logic.
• bluebark_lite.pyx: Cython DSP bridge for reading rtl_power_fftw output quickly.
• setup.py: build script for the Cython module.
• bluebark-lite.service: example systemd unit for boot startup.
• WIRING.md: exact button, OLED, and buzzer wiring for the current configuration.

Dependencies

System packages:

• Raspberry Pi OS or DietPi on ARM64
• Python 3
• rtl_power_fftw
• I2C enabled system
• Build tools for Cython compilation, usually gcc, make, and Python headers

Python packages:

• Cython
• RPi.GPIO
• luma.oled
• Pillow

When you build rtl_power_fftw yourself, you also typically need FFTW and RTL-SDR development packages.

Example install set on Debian-based Pi systems:

sudo apt update
sudo apt install -y python3-dev python3-pip python3-setuptools gcc make libffi-dev libjpeg-dev zlib1g-dev
python3 -m pip install --upgrade pip
python3 -m pip install cython RPi.GPIO luma.oled Pillow

Quick Start

1. Put this folder on the Pi, for example at /root/bluebarklite.
2. Enable I2C.
3. Install the Python and SDR dependencies.
4. Build the Cython module:

cd /root/bluebarklite
python3 setup.py build_ext --inplace

5. Run the app:

sudo python3 bluebark_lite_app.py

systemd Startup

The included service file is meant as the starting point for boot startup.

sudo cp bluebark-lite.service /etc/systemd/system/bluebark-lite.service
sudo systemctl daemon-reload
sudo systemctl enable bluebark-lite.service
sudo systemctl start bluebark-lite.service
sudo systemctl status bluebark-lite.service

Default Buttons configuration

• Shutdown button short press shows CPU temperature briefly and gives one beep.
• Shutdown button long press triggers shutdown after about 2 seconds.
• Mute button short press toggles mute.
• Mute button long press rotates the OLED display.
• Mode button short press raises the squelch floor in 2 dB steps and wraps back to the minimum.
• Mode button long press toggles between NARROW and WIDE SDR modes.

Tuning Notes

• TESTPMR is aimed at the 446 MHz PMR range.

rtl_power_fftw scans the selected frequency range - binary sweep data goes into a RAM FIFO - Cython reads the FIFO and extracts the strongest peak - Python handles display, buttons, threshold, and buzzer.

Important: this is a signal presence and strength monitor only. It does not decode, demodulate, or reconstruct TETRA voice or data content. This repository is provided as-is.

License

MIT