Libra

Open-Source Pocket Size Kitchen Scale for Nutrition

Precise food & nutrients intake monitoring made easy

Open-source

hardware and software

Bluetooth 5

low energy consumption

Pocket-size

smaller than most smartphones

The importance of portion size estimation

Energy balance and nutrients intake

Balance in energy intake and energy expenditure is crucial to maintain a healthy weight. We often don't meet our energy needs and consume larger amounts of food, without being aware of it. Which leads to weight gain. The ability to accurately estimate the portion size is very important to be aware of how much food we consume, and therefore help us not only to control body weight but also to follow dietary recommendations and guidelines. Moreover, accurate portion size estimation is crucial also for health care professionals to accurately assess patient's energy and nutrient intake.

Why is portion size estimation so problematic?

Grams, cups, spoons, servings ...

Estimating and selecting the appropriate portion size can be confusing due to the existence of inconsistencies between measurements units. Different measurement units are used around the world, and although most countries use the metric system, household measures such as cups and spoons are frequently used as food measures. International difference in the size of measuring cups can be even more confusing for consumers and many European countries do not use cups in recipes, in dietary recommendations or on food labels, which makes the assessing of food portions even more difficult. In addition, the various terminologies and definitions for food portions, such as standard serve sizes; portion sizes; recommended serve sizes, can confuse the consumers even more.

Enter Libra

A handy, portable, and easy to use solution to portion size estimation

Portion size estimation is very important for weight control and prevention of obesity-related health problems. Portion size education and interventions can have a positive impact on reducing the energy intake and improving the ability to estimate portion sizes. Also with the use of portion size measurement aids (PSMA). Frequently used PSMAs are household measures such as measuring cups, spoons or glasses; food models; rulers; bean bags; wedges; thickness sticks; food photographs or common objects (e.g. tennis ball, card). Despite the fact that PSMAs are useful, a lot of them are not practical for regular use which makes them less likely to be used outside the home.

Some specifications

Enabling small size and energy efficiency

The scale hardware is developed using few highly integrated components to reduce energy consumption. The major parts of the scale are: the Bluetooth low energy (BLE) SoC, power management circuit (PMIC), and precision measurement circuit. The Nordic nRF52 SoC integrates a microcontroller build around an ARM Cortex M4 CPU, numerous peripheral devices, ISM band radio, and and internal power supply. It supports Bluetooth 5 with higher throughput, which shortens transmission time and reduces power consumption. The power consumption of the SoC is further reduced by using internal DC/DC converter for the power supply. The MAX77734 power management circuit integrates Li+ battery charger, adjustable low-dropout linear regulator (LDO) and current sink. It was chosen as a compromise between power efficiency and device cost (e.g. MAX77640 device has more efficient DC/DC converters but it is more expensive). The HX711 is a precision analogue-to-digital converter (ADC) designed to interface with a bridge sensor.

The scale design also includes some optional parts like Wi-Fi charger and physical buttons. They provide additional functionality at the expense of cost and power consumption. If such functionality is not needed, they can be omitted at production. The power consumption was further lowered by switching off the unused devices.

Dimensions 117 mm x 69.2 mm x 9.4 mm
Weight 73 g
Max load 5 kg
Precision 1 g
Battery Li-Ion 500 mAh
Connectivity Bluetooth 5, USB-C
Clients Android more soon

1. Build your own

The firmware , circuits, 3D printable housing and sample Android client are all open-sourced and freely availble.

Get blueprints

2. Purchase one (or a dozen)

Ballerina assembled and ready for use in your life, research project or integrated with your commercial software.

Get Ballerina

3. Thinker with the dev kit

Adjust Ballerina to your needs. The kit includes full functionality like wireless charging and physical buttons.

Get development kit

Trusted and supported by

The TETRAMAX project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 761349.