A hot tub with a smartphone in front showing real-time sensor data

ESP32 Keeps Track Of Hot Tub’s Vital Signs

October 1, 2023 by Robin Kearey 11 Comments

Like swimming pools, hot tubs need regular monitoring to ensure their water stays clean and clear. An average person might take a water quality reading once or twice a week using test strips, but such a low sampling rate obviously won’t do for a hacker. [Stephen Carey] has therefore built a hot tub monitor that checks the water quality every minute and reports it on a neat mobile dashboard.

[Stephen]’s system uses commercially available sensors that track pH levels and Oxidation-Reduction Potential (ORP), both basic measurements that indicate water quality. A second set of sensors keeps track of the temperature of the water and the outside air, which should help in finding insulation failures and keeping energy use under control.

An ESP32 reads the sensors and sends out the data through WiFi. [Stephen] programmed the ESP32 in MicroPython, using an MQTT driver to connect it to Home Assistant. By looking at the graphs generated, you can tell when someone entered the tub from a step change in pH and ORP. It’s even possible to generate alerts when any of the values drift outside their acceptable range – we can already imagine an alarm going off when someone enters without having showered first.

The system also has a calibration mode to check the sensors against a well-defined buffer solution. As with many chemical sensors, the pH and ORP probes gradually lose their active material and need to be replaced after about a year. Good ones aren’t cheap, but [Stephen] has found pretty decent low-cost alternatives on AliExpress that should be fine for a home setup.

If you also want your tub or pool to be actively managed, you’ll need a more complex system, perhaps even one that can also dispense chemicals. If your hot tub is heated by a wood fire, however, all you need is a way to alert the person tending the fire.

Wood-Fired Hot Tub For The End Of The World

August 8, 2020 by Jenny List 13 Comments

It’s one of the idyls of our age, to imagine oneself lounging in a hot tub watching a golden sunset, glass of wine in hand and the love of your life at your side. Along the way though it’s one that’s become diverted from the original, instead of a Scandinavian style wood fired tub in the forest we’re more likely to be thinking of an electric whirlpool spa made from fibreglass, as much a status symbol as a leisure item. It’s refreshing then to see [sirClogg]’s home made hot tub, a simple wooden tub with associated wood stove to heat its water. We can’t wait to step in!

The tub is simplicity itself, being made from softwood planks held together under tension by some steel cables. He admits though that he made a mistake using green wood, as it has now contracted leaving the tub with some gaps. But it’s a simple enough build that he can contemplate dismantling and rebuilding it to correct for that oversight.

Heat meanwhile is provided by a pipe that circulates water from the bottom of the tub through a heat exchanger coil inside a brick-built wood stove adjacent to the tub. The fabrication of the heat exchanger is detailed in the video below, we enjoyed seeing the copper piping filled with salt to ensure it doesn’t collapse when being bent around a five-gallon bucket. It doesn’t get much simpler than this, and the reward of a hot tub must be a sweet one indeed.

For hot tub enthusiast hackers, it’s always worth remembering that the excellent Danish hacker camp BornHack has a hot tub as part of its wellness area.

Continue reading “Wood-Fired Hot Tub For The End Of The World” →

The Danish Internet Of Hot Tubs

August 24, 2019 by Jenny List 2 Comments

Every hacker camp has its own flavor, and BornHack 2019 in the Danish countryside gave us the opportunity to sample some hacker relaxation, Scandinavian style. Among the attractions was a wood-fired hot tub of gargantuan proportions, in which the tired attendee could rejuvenate themselves at 40 Celcius in the middle of the forest. A wood-fired hot tub is not the easiest of appliances to control, so to tame it [richard42graham] and a group of Danish hackerspace friends took it upon themselves to give it an internet-connected temperature sensor.

The starting point was a TMP112 temperature sensor and an ESP8266 module, which initially exposed the temperature reading via a web interface, but then collapsed under too much load. The solution was to make the raw data available via MQTT, and from that create a web interface for the event bar, Twitter and IRC bots. There was even an interface to display hot tub temperature on the ubiquitous OHMlights dotted around the camp.

It’s more normal to control a hot tub via an electric heater, but since the wood fire on this one has to be tended by a camp volunteer it made sense to use the IRC system as an alert. It will be back at BornHack 2020, so we’ll have to do our job here at Hackaday and spend a long time lounging in the hot tub in the name of journalistic research to see how well it works.

Fill Your Hot Tub With Sand. For Science!

December 8, 2017 by Lewin Day 62 Comments

Here at Hackaday, we can understand if you don’t like sand. It’s coarse, rough and irritating, and it gets everywhere. With that said, [Mark Rober] discovered a great way to have fun with sand right in your own back garden.

We’ll preface this by stating that this isn’t the easiest hack to pull off on a lazy Saturday afternoon. You need a spare hot tub, plenty of pipe, and a seriously big air supply. But if you can pull it all together, the payoff is fantastic.

What [Mark] has achieved is turning a regular hot tub into a fluidized bed. In simple terms, this is where a solid particulate material (like sand) is made to act more like a fluid by passing pressurized fluid through the material. Through a carefully built series of drilled copper pipes, [Mark] manages to turn the hot tub into a fluidized bed, much to the enjoyment of his young nephews.

While it’s not the easiest hack to copy at home, [Mark] drives home the science of both the fluidized bed and why certain objects float or sink in the sand. It’s something that can also be easily tackled at a smaller scale, if you’re looking for something more achievable for the average maker.

For more sand science, how about using it to hold up your car?

[Thanks to Keith for the tip!]

Carpool DeVille: The World’s Fastest Hot Tub

July 14, 2014 by Eric Evenchick 27 Comments

Back in 1996, a group of engineering students at McMaster University set out to build a fully functional hot tub housed in a working car. They chopped up an abandoned 1982 Chevy Malibu and converted it into The Carpool.

That group of students graduated, and began work on the Carpool DeVille. Six years later, they’re ready to take it to Bonneville Salt Flats to claim the title of “world’s fastest hot tub.”

There has been some substantial modifications to the vehicle to make the Carpool a reality. A custom fibreglass tub was built to drop into the passenger compartment, and heat exchangers were added to the stock engine system to heat the water. The plumbing and pumps for the tub reside in the truck, while the original V8 engine is up in the front. A custom air suspension system allows them to carry the massive volume of water. There’s even a marine throttle to control gas and brake from the driver’s seat in the tub.

The folks behind the Carpool DeVille ran a Kickstarter to fund their race costs. The campaign is over, but you can still check out the story and pictures of the conversion. Since it was a successful campaign, we’re looking forward to seeing this custom vehicle out on the salt flats.

Spaduino Heats Up A Used Hot-tub

November 14, 2011 by Mike Szczys 38 Comments

[Ryan] and the roomies decided that a hot tub was just what they needed to spice up the place. They hit Craig’s List and found one for the right price. After acquisition and setup they were pleased to find that the jets and pump worked great. But you’re not going to want to stick as much as your big toe into this ice-cold cryogenics experiment. Some poking around in the control system exposed the dead relays which are responsible for switching the heater. Instead of swapping the parts, [Ryan] began building a control system that will replace the twenty-year-old original.

The heating element still works, but it’s rated at 5.5 kW and here’s no way to automatically switch it on and off. [Ryan] found a 60 Amp solid state relay which can handle the load, and plays nicely with his Arduino. Initial tests got the tub up and running again. Obviously you want the tub to maintain temperature and so a thermistor was added to take readings from the heater core. There’s also a potentiometer to adjust the temperature, and an LCD screen to show the current settings. But [Ryan] hopes to add more features over time, like incorporating jet control, and adding wireless communications via an Xbee module.