Semi-pseudonymous software program developed and radio ham Stephen D. has constructed and efficiently examined a Silicon Labs RF4463-based transmitter for beaming real-time video from a Raspberry Pi strapped to a high-altitude balloon — efficiently receiving VGA-resolution footage at 12 frames per second (FPS).
“For months I have been engaged on a system that may transmit actual time video to the bottom from a excessive altitude balloon,” Stephen explains by the use of background to the airborne mission. “Final weekend, on Saturday, September 9, we did a check launch of this method. The core system labored completely and I recognized some enhancements to make. Different individuals are nonetheless evaluating how their techniques did, and I hope they went in addition to mine!”
The balloon’s payload is predicated on an earlier effort which paired a Raspberry Pi Zero single-board laptop and Raspberry Pi Digital camera Module with an STMicro STM32 microcontroller driving a Silicon Labs RF4463 transceiver for static imagery transmission. “We’re utilizing an RF4463F30 module to transmit FSK [Frequency Shift Keying]-modulated packets within the 70cm band at 1W,” Stephen explains. “These packets are LDPC [Low-Density Parity Check]-encoded for error correction.”
In its newest incarnation, although, the setup has obtained a serious efficiency improve via the transfer to a Raspberry Pi 4 Mannequin B — a bigger and extra power-hungry mannequin within the widespread SBC household, however one which boasts far more reminiscence and compute efficiency. Video is captured from the digital camera sensor and encoded into H.264 by GStreamer, then obtained on the bottom and decoded utilizing the identical software program — each for reside on-screen show and for streaming to disk, in order that the footage may be reviewed at a later date.
“At present it pegs the [Raspberry Pi 4] CPU at round 50 per cent,” Stephen writes, “however the hope is to finally transfer to GPU transcoding to avoid wasting energy — and warmth! The video is encapsulated in an MPEG-TS stream to permit sleek restoration from packet loss. The video is 640×480, 12FPS, with a most bitrate of 200kbit/s, although GStreamer appears to exceed this at instances.”
The balloon’s payload was recovered post-flight — with somewhat effort. (📷: Stephen D.)
In testing, the transmitter remained useful even when the balloon reached a 50km (round 31 mile) distance from the receiver — with Stephen believing it ought to proceed to work at even longer ranges. “We wish to stream the following launch to YouTube,” he notes of future plans for the mission. “To facilitate this I will add an RTSP [Real Time Streaming Protocol] server to the bottom station. I determine I can use current software program to eat this stream and pipe it to the Web.”