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Tired of replugging your multimeter when you want to measure both voltage and current on a small project? Tiny V/A meter is the device you need!

There is nothing new about the INA219 high side current sensor. There are plenty of good projects out there that utilizes its ability to measure both current and voltage on a load. I originally got inspired by youtuber Julian Ilett and his “10 Minute Arduino Project - INA219 Current Sensor” video. But I wanted a compact meter with a simpel interface and a 3D printed case - so I decided to make that myself.

About the INA219 sensor:

In the high range setting the INA219 is able to measure ±3.2A with a resolution of 0.8mA. But in the ±400mA range the resolution is 0.1mA. It does this by measuring the voltage drop over the 0.1 ohm resistor on the PCB. So the sensor will introduce a very small voltage drop but only 320 mV in worst case (3.2A). As an example at 100 mA the drop is only 10 mV. If you want to, it is possible to change the resistor to get higher range or resolution. At the same time the sensor is also measuring the bus voltage with a resolution of 4 mV. In my experience the voltage readings are very precise. The precision of the current readings depend on the actual resistance of your resistor. They are typically with 1% tolerance (but not sure you should trust the cheap eBay boards). I believe it should be possible to calibrate the results if you know the precise value of the resistor. But I didn’t dig further into that as the precision has been good enough for my needs.

Features of the Tiny V/A Meter:

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 sensor.
Settings are stored in EEPROM and reloaded on boot
Serial interface
Prints results on serial. Can be used for logging.
Change settings with serial commands
- 1x Arduino Nano - Arduino Nano eBay example
- 1x INA219 sensor board - INA219 purple sensor board eBay example
- 1x OLED 0.96” I2C 128X64 4-pin - OLED 0.96” Blue I2C eBay example
- 1x TTP223 Capacitive Touch Switch - TTP223 Capacative touch button PCB eBay example
- 1x Female Power Supply Jack Socket Mount - Female Power Jack hole mount eBay example
- 1x Male Power Supply Jack - Male Power Jack with screw terminals eBay example or Male Power Jack with Push terminals eBay example
- 1x Slide Switch 2 Position 6 Pin - Slide switch 6 pin eBay example

- 1x 5 pin male connector (optional) - 2.54 male pin headers eBay example
- 1x 5 pin female connector (optional) - Dupont connector set eBay example or 2.54 5 pin single row connector eBay example
- Heat shrink tube (optional)

- Solder iron
- 3D printer (if you want the 3D printed case)
- Glue gun”

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