PowMeter for Nano

I do have these questions in mind every time I study a new Arduino project. Low power consumption is often advised (see how to save power on an Arduino board). But every time, I have to fast tinker a circuit with a couple of multimeters. It takes me 10 minutes to check if everything is okay, then it doesn’t work, likely because the probes are not properly connected or because I miss so many burnt calibres on my multimeters… There are wires everywhere around. Even though I have 2 multimeters plus my oscilloscope DMM, there is always something wrong!

Beside this I have been interested by power consumption measurement. The matter is harder than expected and I got bad measurements at first. Probably like you, I first thought about conceiving a circuit. I rapidly found that measuring a current on a rail that is higher or equal potential to the measurement circuit power is difficult particularly if one looks for precise measurements. But I found a large quantity of published circuits. Most of them are complicated. If you are interested by this topic, you will certainly appreciate this Analog Device Application Note detailing tens of standard circuits.

Hopefully, there are currently high performance dedicated ICs. There are quite a lot of them, many being designed by Texas Instruments. Finally my choice went to the quite standard INA226 IC used by many Arduino makers. I chose it mainly because it would integrate into an “all I2C” architecture.

The board is equipped with two INA226 ICs, an Atmega microcontroller and an OLED module. All these are communicating through I2C. Measurement is done through sense resistors with a power of 1W despite their small 1206 package footprint. This let me hope not to burn them so easily as my multimeters calibers. Of course, short circuits should be avoided!

Main specifications are:

• USB:
  • Current band: 0 – 500 mA, can be modified up to 800 mA and more
  • Resolution: 0.025 mA

•  VIN:
  • Current band: 0 – 8 A
  • Resolution: 0.25 mA

• Voltage:
  • Voltage band : 0 – 24 V
  • Resolution : 10 mV

• Other:
  • Measurement error :  less than 1%
  • Display resolution 3 to 4 digits
  • Dimensions: 69 mm * 18,2 mm * 18.5 mm
  • Weight: 10 grams

Advantages of this solution:

• A very small footprint. The Shield is installed on the same place as the Nano board. It is only 26 millimetres longer .
• Allows you to monitor USB voltage and current when powered through the USB port.
• but also the power consumption on the VIN MON pin (added).
• and the power consumption of the peripherals connected tot the VAUX pin (added).
• It does not consume any of your project software resources thanks to the onshield MCU. It draws less then 10 mA.
• All components are communicating through I2C. This means that you can take actions inside your own program depending on current or voltage values retrieved from the components.
• Good measurement precision.
• You can use the onshield OLED within your own project.
• The OLED can be rearranged on the other side of the board.

Some PowMeter Applications

Configure your shield

PoweMeter is equipped with an Atmega168 chip, so you can change the firmware as you like (using an ISP programmer) and tinker the function of the shield as needed. You might also use the OLED to display any information you would like related to your project. You can communicate with any I2C components on the board directly. The resource pack includes a console library that you can use to load a console program on your Nano board to configure the PowMeter shield and define:

• The display layout: either USB and VIN, only USB or only VIN:

• Set up an alert: for example here we set up an alert to trigger if USB voltage was under 6V (unrealisitc):

• Retrieve USB and VIN voltage and current values to use them on you own program.
• Put the Shield into sleep modes.
• Calibrate the device.

Some use cases

• RC vehicles that needs to monitor the power consumption periodically like a solar plane.
• Arduino robots with power efficiency concerns.
• Coud be used in STEM course to allow convenient power monitoring without worying about the proper use of a couple of multimeters.
• IOT project with permanent power monitoring.
• Any kind of Arduino based portable equipment.
• Circuit validation on breadboard at the design stage.
• As a replacement for up to 4 multimeters.