Monitor voltage and current with the Tiny V/A Meter

Measuring voltage and current is an important part of the development process for any hardware product. Especially when developing a low power device, the knowledge of how much power the device is drawing at each mode of its operation is critical to the correct estimation of its battery life.

While voltage can be measured in a straightforward manner, current usually require a more strenuous approach with a shunt, which if not properly selecterd could lead to errors. Even when these two are properly calibrated in the form of a meter, the tethering wires between the device and the meters can make the process not so interesting, especially when you have to do it repeatedly. To solve this, Karl Torp decided to build a palm-sized, one-for-all meter called; the Tiny V/A.

Based on the Arduino Nano, the TinyV/A comprises of the nano, an INA219 sensor, a 0.96” OLED display, and a single capacitive touch button, all neatly housed inside a 3D-printed printed enclosure. It operates in a manner similar man-in-the-middle technique, taken in input from a power supply via a female barrel jack connector and supplying power to the load through a male connector output.

The INA219 is a popular high side current sensor, readily available on Platforms like Alibaba, and its ability to measure both current and voltage on a load is the rock upon which the project is built.

Another interesting element featured in the project is the single capacitive touch buttons which are meant to allow users to easily navigate the Tiny V/A’s menu and change certain settings like the sensor range and refresh rate.

Some features of the tinyV/A meter include:

• It can be powered from USB or from the power input.
  • When supplied from USB the input supply can range from 0 – 26V. Only leak current of sensor affects the power input. Nice if you want to verify the capacity of a battery.
  • When supplied from power input this can range from 4 – 15V. (Limitations of arduino voltage regulator).
  • Selected input is detected on boot or change and will display a range message to the user.
• Can display voltage, current, power & mAh simultaneously.
• mAh can be reset.
• One button interface with short/long press.
• Select INA219 ranges: 26V / 3.2A, 26V / 1A or 16V / 0.4A
• Select sampling rate 100, 200, 500 or 1000 ms.
• Enable/disable sensor sleep to lower leak current in the sensor.
• Settings are stored in EEPROM and reloaded on boot
• Serial interface
  • Prints results on serial. It can be used for logging.
  • Change settings with serial commands

The project is entirely open-source and all the design elements including schematics, BOM, firmware, build guide, etc., that you may need to replicate it, is available on the project’s project’s page.

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