Minimax Salt-indicator IoT prototype

Rick van Gemert Rick van Gemert
27 - 06 - 2018

For one of our customers we’ve prototyped a network connected monitoring device for their water softener: Minimax. It checks your salt level to make sure your softener never runs out and can continuously provide you with soft water throughout the day, every day.

Hard water

Hard water is caused by a high mineral content in the water. It can affect the taste and smell of the water, but can also affect the functioning of appliances. To solve this problem, Minimax built a water softener. It reduces the mineral content in the water using blocks of salt without needing to be connected to a power source. This allows you to place the water softener wherever it makes the most sense, often in the basement, without having to worry about a power supply or making sure its batteries are charged.


Although the device is great at softening water, it does not provide you with monitoring tools to keep an eye on it. If you want to know when you have to refill your salt, you have to physically walk to the Minimax and look into the device to see if there is any salt left. Many people, myself included, love to have information readily available at their fingertips but this is just not possible with the Minimax as is. This led us to start prototyping and build a solution for the problem.


The most important feature for the prototype is measuring the salt level in the device. To tackle this, we’ve used an ultrasonic distance sensor. The sensor triggers a sound and listens for its echo. Using the interval between them it can calculate the distance to the object. When the salt level decreases, the distance between the salt and sensor increases. The sensor is read by an ESP32. The ESP32 is a microcontroller with built-in Wifi and Bluetooth allowing us to send the data to the user.

Besides an app which shows the salt level, the device also contains a physical indication of your salt level. A green, orange or red light indicates if the salt is sufficient, needs to be refilled or is almost depleted. This allows you to see if you need to refill your salt whenever you walk past it.

Next steps

As a basic prototype, the device meets the criteria. However, it is not limited to measuring just the salt level. By adding additional sensors, like a water hardness or pH sensor, it can provide insights into how effectively the device is functioning. Minimax can then use this information to continuously improve their product.

Rick van Gemert. As a developer at El Niño, he loves to make the life of users a bit better by building IoT prototypes and creating optimal user experiences. Rick van Gemert. As a developer at El Niño, he loves to make the life of users a bit better by building IoT prototypes and creating optimal user experiences.

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