The Purple Grinder

Creator and Developer

The Purple Grinder is a smart coffee grinder. It was created as a low-cost and high-performance alternative to commercial grinders. TPG uses a Hario Slim grinder and can be controlled by an app.


My goal with TPG was to create a very simple and straightforward device: it has just one activation button. After activated, the grinder runs by the configurated time - that can be changed using an app - that can vary from 1 to 5 minutes.

Even the building is very simple: the only modification that has to be made in the Hario Mill is the installation of a spring pin in the central axis.

Connecting and changing the TPG parameters with the app is also very simple: just points the smartphone camera to the special QR-Code in the device. After that, the app just connects to the 802.11 network of the device and then is possible to configure the TPG.


This project took 60 hours of work. All the design, hardware integration, and software development were made by me.

I designed it with Fusion 360. All parts have been printed with an Anycubic Kossel Linear Plus 3D printer.

I used an ESP8266 microcontroller. The code was made in C++11. I configurated the ESP8266 in AP mode and the implemented a REST web service API in it.

The Android app was made with Kotlin.