UncleStem's AR Sandbox Turns Kinetic Sand Into a Live Topographic Map

You probably know what a development sandbox is, but you’ve never seen one quite like UncleStem’s. After seeing a demonstration in which UCLA researchers used a depth-sensing camera and a digital projector to map real-time topographic data onto a physical box of sand, UncleStem decided to build a budget-friendly version of his own. When you pile up the sand, mountains form, and digging trenches creates rivers and lakes right before your eyes — no glasses or goggles needed.

Rather than relying on the expensive commercial depth cameras research projects use, the creator centered the build around a miniature Time-of-Flight (ToF) sensor capable of reading distance across an 8×8 matrix. By firing infrared light and measuring the return time, the sensor captures the contours of the sand surface in real time.

To display the terrain, UncleStem picked up a tiny secondhand pico projector for only about $20. The bargain came with a problem, however: the projector’s internal battery had swollen badly from heat buildup. After opening the device, UncleStem removed the damaged cells, replaced them with new ones matched to the original specifications, and reused the existing battery management system board. Once repaired, the projector was mounted overhead on a tripod to cast terrain graphics onto the sandbox below.

Aligning the sensor and projector proved to be one of the project's toughest challenges. UncleStem designed a custom articulated mounting arm in Fusion 360 and 3D printed it with multiple pivot joints for fine adjustments. The sensor was mounted beneath the projector rather than in front of it, preventing unwanted shadows from interrupting the illusion.

Initially, the system used an Arduino Nano, but the tiny 8-bit microcontroller struggled to process the stream of 64 simultaneous depth readings fast enough. Compilation issues and sluggish performance eventually forced a hardware upgrade to an ESP32-C3 board, which provided enough processing power and memory to handle the workload smoothly.

To complete the illusion, UncleStem developed software capable of translating raw sensor data into a colorful topographic map. Lower terrain levels became blue lakes and rivers, mid-level elevations appeared as green plains while taller peaks shifted into brown mountains and snow-capped white summits.

On the first test, calibration was a problem because the sensor viewed the sandbox from a slightly different angle than the projector. To compensate, the system used four physical corner markers to align sensor coordinates with projected pixels. A later “zeroing” feature allowed the creator to flatten the sand and establish a baseline terrain level, eliminating the false appearance of a sloped landscape caused by the angled mounting arrangement.

The finished system runs at roughly 15 frames per second and transforms 25 kilograms of kinetic sand into a fully interactive miniature world that reacts instantly to every scoop, trench, and mountain ridge. Be sure to watch the video to the end — this is one you won’t want to miss!