A water softener is a fairly common piece of equipment found in many homes. Fill it with a bunch of salt, and all those calcium ions will be replaced with sodium ions. Your soap lathers now, and you might just get rid of those deposits on your coffee pot.
While a bag of salt may last a month or so in a water softener, you can’t know what you don’t measure. That’s what led Erik Lemcke to create the Salt Sentry, an IoT gizmo to monitor the level of salt in a water softener.
For measurement, the Salt Sentry uses a Time-of-Flight laser-ranging sensor to measure the distance from the water softener to the salt block. It’s a simple solution, and more than accurate to tell you if you’ll need to fill up the water softener in the next week or so.
The brain of the Salt Sentry is an Espressif ESP-WROOM-02, incorporating an ESP8266 microprocessor in a small package. This module sets up a web server that’s accessible over WiFi, and has support for MQTT, so your home assistant of choice will tell you when to buy more salt. You can check out an example of what the web interface looks like in the panel to the left.
Because the ESP8266 is well-supported by the Arduino IDE, the Salt Sentry is also fully hackable, with six GPIO pins broken out onto an internal header. If you want to expand the Salt Sentry to provide more measurement, go for it. Add a light sensor, so you know when the basement light is on. There’s already a really, really awesome manual for the Salt Sentry available and a bit more information available on how to connect it to your network.
