Title: (This was previously submitted as <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=2246856" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=2246856</a>)<p>The Ravenna Ultra-Low-Altitude Vehicle is a backyard rocketship treehouse nestled in the Seattle neighborhood of Ravenna. Click the link to see a demo video (<a href="http:&#x2F;&#x2F;rocket.jonh.net" rel="nofollow">http:&#x2F;&#x2F;rocket.jonh.net</a>).<p>The hexagonal treehouse is about 6.5 feet (2 meters) across at its widest point. The frame is welded mild steel with riveted aluminum siding. It contains nearly 800 LEDs forming dozens of numeric displays spread across 14 control panels, each with an acrylic face laser-cut and etched with labels such as &quot;Lunar Distance&quot; and &quot;Hydraulic Pressure&quot;. The pilot controls the rocket using a joystick and panels full of working switches, knobs and buttons. Underneath the capsule are three &quot;thrusters&quot; that shoot plumes of water and compressed air under the control of the pilot&#x27;s joystick, simulating real positioning thrusters. Takeoff and docking sequences are augmented by a paint-shaker that simulates the vibration of a rocket engine. Sound effects complete the illusion, with a powered subwoofer that gives the rocket a satisfying rumble.<p>When it was built in 2011, rocket operations were controlled by three Atmega328 microprocessors on custom-fabricated printed circuit boards, running a small operating system, RULOS, built just for this project.  A trench running from the house to the rocket carries 12VDC power for the lighting and electronics, water for the thrusters, compressed air, and several data signals.<p>Since 2011, the two-person team has upgraded it, here is a recent update from the makers:<p>One of the most visible changes is replacing the primary 4-line display with a slicker 6-line display (i.e., 6 rows of 8 columns of 7-segment LEDs). The audio synthesizer has been upgraded to a PCB that can generate 50khz, 16-bit audio. The interconnection bus, which had been flat IDC cable carrying individual on&#x2F;off lines, was upgraded to a true I2C-based networked distributed system with over a dozen individually addressable targets, all interconnected by standard cat5 cable that carries both our I2C protocol and power. We also moved much of the electronics from 8-bit atmega328s to newer, 32-bit STM32F3&#x27;s. RULOS has been expanded into a pretty general purpose embedded systems platform ported to 5 major lines of CPU (atmega, attiny, stm32, nxp lpc, and esp32). We&#x27;ve used it for dozens of other projects in the last 12 years, including a nanosecond-accurate timestamper, a GPS datalogger, an air quality sensor, various little electronic control boards for toys (e.g. these, and this), and an autonomous boat (that sank). It is all available on Github: <a href="https:&#x2F;&#x2F;github.com&#x2F;jelson&#x2F;rulos">https:&#x2F;&#x2F;github.com&#x2F;jelson&#x2F;rulos</a>.
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