Getting Custom (Swimming Pool) Tempetures onto Apple Watch.

I’m not going to lie, Apple have really locked down the Apple Watch, and made it very difficult to automate a workflow of getting a DIY Temperature sensor to a complication on an Apple Watch. Rest assured there is a solution, but it does require a one time in App purchase to get complication support.

The work flow is farily straight forward, you need to read the temp, upload it to a common platform that can be read by a third party App that supports complications on the Apple Watch. It took me a little research to workout what sites are supported by what App’s and of those which ones has watch support.

The first part of this process can be skipped if you have a prebuilt temperature sensor that supports the Weather Underground service.

Solution (From the Ground Up):

My pool temperate is read by a customer built arduino board using a DS18B20 temperature sensor. It’s has some fancy add on bits like solar charging and li-ion battery support. But at it’s basis it’s a cheap lilon D1 Mini with a DS18B20 sensor connect to it. The D1 Mini supports WiFi (important) and can be powered by a basic 5V USB-C adapter, it is a few dollars on eBay / Aliexpress etc.

The DS18B20 Temperature sensor comes in a number of package styles depending on your application, since I’m monitoring a pool I have an enclosed waterproof unit with a 3 meter lead.

The Arduino IDE has code examples for the DS18B20 and obtaining plans and further details is very easy using Google. It is one of the most widly used DIY sensors. Of course you can use any temperature sensor you like.

Once I have my ardiuino reading the temperature the next step is to get the temperature recorded somewhere a Watch App can use. Weather Underground (WU) appears to be most supported. So I signed up for WU account and added a new “weather station”. When you add your new device you can upload data to it via HTTP in the following format:

weatherstation.wunderground.com/weatherstation/updateweatherstation.php?ID=XX&PASSWORD=XX&dateutf=now&tempc=12%2E44&action=updateraw

The ID and PASSWORD (Key) can be found for your new device on WU.

So get your Sensor Data uploading to WU from your D1 Mini. This requires a little extra coding to connect your D1 to your Wifi and then have it post data to the URL above. Again all the nessasary code is avaliable via Google, or youtube in some cases. There are lots of examples out there.

Once you have data in WU you will be able to view it, see the plot over time and keep track of your sensor.

OK, I got my temperature data into Weather underground, now what?

Now it gets a little easier. All you need is an iPhone App that supports WU with complications. For this I use ‘My Personal Weather Station’ or MyPWS. Once you have installed the App, you can add your WU station in the App for access on your phone, and then enable the watch complication add on (fee involved). Once you have the App add on for watch support you can then modify a watch face to add the MyPWS complication (make sure you add the MyPWS App to your watch).

Done, your custom temperature should start appearing on your Apple Watch.