This Smart BLE Water Bottle Upgrade Tracks Your Hydration with an ESP32 and a Time-of-Flight Sensor

Called the SMRTcap, this replacement lid for off-the-shelf water bottles lets you track your drinking on the way to hydration goals.

Pseudonymous mechanical engineer "tanstin" has upgraded their water bottle with a bit of clever technology designed to encourage good hydration habits: a Bluetooth-enabled sensor hidden in a replacement lid, dubbed the SMRTcap, to track how much drinking they do in a day.

"I don’t need to track my water to the decimal," tanstin admits of the project. "However, I am also the person that has a tendency to wake up, eat breakfast, have 3-4 cups of coffee, then get completely lost while hyper fixated at work. Then 8PM rolls around and I’m obviously beyond behind on how much water I should have drank during the day. Sometimes it’s not hitting the goal mark to the T, every day. It’s just to convince me to drink."

The build takes the form of a 3D-printed replacement lid for an off-the-shelf water bottle — currently in the advanced prototype stage, to be replaced at the next iteration with a model that doesn't require additional hardware for assembly before being switched out for a truly food-safe and robust injection-molded version — which hides the integrated electronics.

"[There's a] Time of Flight [ToF distance] sensor to the top of the [water's] surface," tanstin explains, "with a gyro to make sure it's not moving." The microcontroller, meanwhile, is an Espressif ESP32, which connects to tanstin's smartphone over Bluetooth Low Energy (BLE) to track water consumption and compare it to a configurable goal.

"I’ve been working on this for four years," tanstin says, "filed for a patent that I couldn’t end up fronting money for after the provisional, been through 30+ different designs, and have learned so much. Last year I got pretty heavily depressed and told myself to start fresh and start completing projects not for money or for others, but to boost my confidence and keep me moving."

Thus far, tanstin has not released any source code or design files — but they may follow once prototyping is complete. "I was toying around with making a production BLE device, but the $$ it takes for certification and startup is too much," they explain. "Plus, no sense in overproducing when our world has a major consumption problem. That said, yeah, I may put together a repo with all the files and have a donate system.

"When I get the final injection-shot part made […] I may sell a pre-assembled kit that has all parts required, but isn’t programmed. That would give a base for people and would bypass BT licensing costs."

More details are available on tanstin's Reddit thread.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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