A composite video signal generator running on a Raspberry Pi. It reads live aviation radar data (from an RTL-SDR or similar receiver), renders a radar sweep display, and outputs the result as a PAL composite video signal — viewable on any analog TV or monitor with composite input.

Architecture

RTL-SDR (1090 MHz ADS-B)
  → Pi reads aircraft positions
  → radartv.c renders radar sweep + blips in 640×480 framebuffer
  → GPIO composite output (PAL/NTSC via Pi's TV out)
  → Analog TV: real-time radar display

All rendering is done in C with direct framebuffer access. No GPU, no X11, no desktop. The composite output is generated via the Pi’s native TV-out circuitry using pwm_ir_tx pin for video and pcm_clk for audio sync.

Source Files

• radartv.c — ~800 lines of C: composite sync generation, radar sweep rendering, aircraft blip drawing, font rendering (font8x16.inc)
• radartv.conf — Configuration: center frequency, line mode (PAL/NTSC), test pattern
• compile.sh — GCC build with -O2 -march=armv6
• install.sh — Systemd service setup, auto-start on boot

Features

• Real-time radar sweep with persistent trail (fading blips)
• Aircraft tags: callsign, altitude, speed, squawk
• Test pattern mode for display calibration
• Configurable: line standard, color burst, scan rate
• LCD/little display mode via /dev/fb0 for direct HDMI
• Systemd service for headless operation

The Hardware

• Raspberry Pi 3B+ (or any Pi with composite out)
• RTL-SDR dongle for ADS-B reception
• 3.5mm TRRS cable → composite video input
• 5V USB power

What Was Learned

• Composite video timing to the microsecond: front porch, sync pulse, back porch, active video
• PAL color subcarrier generation (4.43361875 MHz — 283.75 cycles per line + 25 Hz offset)
• Pi’s firmware-dictated TV-out configuration via config.txt (pwm_ir_tx, pcm_clk, tvservice)
• The difference between interlaced vs progressive scan and how to pick based on display
• Analog video is a solved problem but has zero documentation for modern software engineers

Status → ✅ Shipped / Running

Deployed as a systemd service on a Pi 3B+. Composite output to a 14" CRT in the workshop. Available as a reference for any Pi→composite video project.