DIY Electronic Hydrometer

GravityMon is an open source brewing software that allows you to build your own electronic hydrometer. With it you can keep an eye on your fermentation progress without wasting a lot of beer on samples. Just integrate it with your favourite brewing software. And its free!!

This builds on the excellent work done by the iSpindle project. Works on hardware based on the iSpindel or the Floaty hydrometer.

If you like my projects and want to support me, please buy me a coffee or sponsor me on github. This will give me energy to continue build new beer related open source projects.

Service integration

A number of popular brewing software are supported and validated, Most of these will work with limited setup.

Examples include; Brewfather, BrewSpy, Brewers Friend, Fermentrack, Ubidots, Thingsspeak and Home Assistant.

Modern User Interface

The user interface is build on modern standards such as HTML5 and REST API's. Its easy accessible when the device when placed in configuration mode via Wi-Fi. There are lots of configuration options available.

Create gravity formula

You don't need any excel sheets or other tools to create the calibration formula for the device. Just enter your measurements and let the device calculate and validate the formula. You can view the result in a graph and visually check if it looks good enough.

Customize data formats

There is a built editor to allow you to customize the data format that is sent to external services. This makes it possible to support any external service without the need for software changes if the services support HTTP or MQTT as transport.

Easy install via brewflasher

Installation has never been easier than via Brewflasher. Just download the software or try the web version. Excellent work by Thorrak.

Download Web

GravityMon features

Migration from iSpindel

Simple upgrade from an calibrated iSpindel setup, formula and gyro calibration settings can be migrated to GravityMon so that the upgrade can be done in a simple way.

New in v1.4

Easy configuration

You can easily access the web based configuration by placing the device on a flat surface or plugging in the charger. When the device wakes up from deep sleep it will start the web server.

Multiple endpoints

The device has the possibility to send data to 5 different endpoints which means you can use multiple services at once.

Gyro temperature

The gyro actually has a built in temperature sensor which can be used instead of the DS18B20. Its quite accurate if the device has had at least 30 seconds to cool down between reads.

Stability detection

To improve stability in readings and movement will be detected when reading the gyro. If movement is detected data will not be sent until data is stable again.


Temperatures can be shown in either Celsius or Fahrenheit and gravity in SG or Plato

Gravity correction

Temperature of the fluid will have an effect on the gravity. There is a built in feature to automatically adjust gravity based on the temperature.

Temperature Sensor

High precision temperature measurement using an DS18B20 sensor.

Web Protocols

Support web standards for sending data; HTTP (Post/Get), MQTT and Influx DB v2

Open Source

Fully open source, free to use and modify in aligment with the MIT licence. Suggestions for new features is appreciated.


Software can be updated over the air (OTA).


Standard REST API for scripted interaction with the device.


Lots of configuration options to tune the operations of the device.


Save your configuration and restore if needed.

Low battery

Enter battery savings mode when low battery is detected so you fermentation can be tracked.

Homebrew Talk

Join the community, get support and discuss the software.

Join HomebrewTalk


Read the documentation and detailed instructions on how it works.

Read the documentation


Join us on github and contribute to the project, request features.

Join us at GitHub

Hardware options - ESP Boards

GravityMon supports a number of hardware options where the standard iSpindle firmware only supports the ESP8266. With some of the ESP32 options you can also add bluetooth broadcast support. It will also support the Floaty Hydrometer hardware design which is based on ESP32.

The ESP32 will allow for more functionallity to be added which is not possible with the limited RAM in the esp8266.

Dont use the ESP32C3 v1.0 board, this has ha faulty antenna and cannot transmit wifi data with high power.

ESP8266 ESP32-D1 ESP32-C3 ESP32-S2 ESP32-S3 ESP32-lite
Stable version v1.4.1 v1.4.1 v1.4.1 v1.4.1 v1.4.1 v1.4.1
Hardware iSpindel iSpindel iSpindel iSpindel iSpindel Floaty
Modern web interface
HTTP Post (2x)
Influx DB v2
Bluetooth - -
DS18B20 Sensor -
Battery Measurement 1)

1) Supported with hardware modification.

Hardware options - Gyro

MPU 6050 (GY-521) MPU 6500