A £130 build cost separates three schoolchildren from equipment that oceanographers pay thousands for. Pinak, Vihaan and Yuvan — aged 10 to 13 and working as the Unboxed STEM Club with mentors Kshitij Varma and Dr Amol Patil — have built Sensea, a DIY underwater explorer that records video and water temperature from the River Cam and a nearby lake called Todd's Pit.

The team noticed a gap between rhetoric and measurement. People talk about protecting oceans and rivers, but rarely have the tools to measure what is happening below the surface. Their answer, as they describe it, is "a low-cost DIY (£130) underwater explorer that would reveal what's going on below the surface of our local ponds and rivers."

The compute platform is a Raspberry Pi 3 Model B+. The choice was deliberate on two counts: affordability and power draw. The board runs off a standard 5V USB power pack, extending deployment time compared with hungrier alternatives. Imaging comes from a Raspberry Pi Camera Module 3, which captures 10-second underwater video clips alongside time-stamped temperature readings from a waterproof DS18B20 sensor.

Waterproofing drove most of the engineering. The housing had to stay completely sealed while letting sensors sample the surrounding water and the camera see through an end cap. It also had to open for battery swaps and sensor insertion, then reseal reliably. The solution is a sealed acrylic tube acting as a transparent pressure chamber. One end closes permanently with a 10.5cm acrylic disc bonded using marine epoxy. A waterproof cable gland drilled through that end passes the DS18B20 probe cable while keeping the joint watertight. The other end uses an expanding drain plug of the sort plumbers use to test pipework for leaks.

The team trusts but verifies. Every deployment follows a leak test regime: the fully sealed tube and cable sit submerged in a bucket for five minutes, and any rising bubbles scrub the dive. Only after that does the rig go into the water inside its protective cage.

Buoyancy took iteration. After experiments with size and weight, the team settled on a 2kg bone-shaped dumbbell to pull Sensea beneath the river surface and hold it steady while recording.

The optics carry a lesson for anyone filming in turbid water. The boys chose manual fixed focus over the Camera Module's autofocus because autofocus struggles with suspended particles. "Fixing the focus gives much sharper and more stable footage," they explain.

Data handling is equally pragmatic. A PCF8523 real-time clock maintains accurate timestamps without an internet connection, so every clip and temperature log carries a reliable time reference. A Python script, sensea_logger.py, triggers video capture, reads the temperature sensor and writes everything to the Pi's microSD card for retrieval after the dive.

Initial deployments already produced results. Comparing temperature measurements between the River Cam and Todd's Pit clearly revealed differences between the two environments — a baseline the team can now track over time.

The roadmap stays cost-conscious. Future additions may include a pH sensor for pollution monitoring, a depth or pressure sensor, and AI-powered species identification, extending the platform from environmental snapshotting toward continuous, multi-parameter monitoring.