Watt-A-Live INA209 Power Monitor Shield Wing

A 6.4A-2uA current/voltage/power monitor based on the TI INA209 with dedicated GND usable as Shield, Wing, Breakout or Breadboard.

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Yes, we want to keep the Watts alive and not kill them (if you know what I mean ;).

The Watt-A-Live is a versatile embedded power monitor based on the Texas Instruments INA209 with full connectivity to the unit under test. It measures the load current through a shunt resistor and has separate GND connections to the power supply and the load to make it a true power monitor.
It is designed as an Adafruit Feather Wing and Arduino Shield. Alternatively it can be used as a breakout board with any other controller that has I2C and optional GPIO connectivity. 2 jumpers can select between 2 different shunts to measure different current ranges.
The new version board is populated with a 0.05 Ohm shunt to measure 6.4A to 200µA. Optionally a 4.99 Ohm shunt can be added for a current range of 64mA to 2uA. Maximum bus voltage is 26V.
An Arduino library is provided to access all registers and measurements, a demo sketch shows how to print data through the serial console easily.

The board enables a wider variety of features compared to the standard INA219 solutions with 2 screw terminals. Most importantly it has 2 dedicated screw terminals for GND connection to measure the bus voltage and power. No need to solder the GND wire somewhere to the breakout board. It also has 16 selectable slave addresses, so multiple units can be used at the same time. And it has additional signalling pins for bus or shunt voltage and power alerts and warnings. It can be used as Feather Wing, Arduino Shield, as breakout board or on a breadboard.

Full feature set:

  • Adafruit Feather Wing and Arduino Uno Shield connector option
  • Current monitor with 2 different ranges for high current and sleep mode low current measurements
  • Rev 2: 0.05 Ohm shunt to measure 6.4A to 200µA. 4.99 Ohm shunt can be added for a current range of 58mA to 2uA (theoretical minimum).
  • Realistically the overall range is 6.4A to 1mA measured or 200uA calibrated with 2% error.
  • Positive and negative current flow
  • Bus voltage and power monitor with 2 dedicated GND terminals
  • Communication interface: I2C up to 3.4MHz
  • 16 I2C addresses selectable through resistor options
  • 6 dedicated signaling pins (SMBus Alert, Warning, Overlimit, Critical, Convert and 1 GPIO)
  • Operating supply voltage 3.0V to 5.5V
  • Optional 4mm Banana plugs for high current feed or bypass
  • Size: 71mm x 54mm (2.8" x 2.1")


Schematics Rev 2.1

Adobe Portable Document Format - 75.21 kB - 09/20/2019 at 15:00


P42 Watt-A-Live(rev2) Documentation.pdf

Madman Chicken-Scratch Manifesto rev2

application/pdf - 919.85 kB - 09/18/2019 at 01:53


P42 Watt-A-Live(rev1) Documentation.pdf

Madman Chicken-Scratch Manifesto

application/pdf - 1.87 MB - 07/08/2019 at 00:19



Assembly drawing rev1

Adobe Portable Document Format - 24.26 kB - 07/03/2019 at 18:51



Schematics rev1

Adobe Portable Document Format - 90.01 kB - 07/03/2019 at 18:51


  • 1 × TI INA209 26V, Bi-Directional, Low-/High-Side, I2C Out Current/Power Monitor & High-Speed Comparator
  • 1 × Arduino Shield connector set Female header with long pins
  • 1 × Feather Wing connector set Female header with long pins

  • More current testing

    MagicWolfi11/30/2019 at 18:34 0 comments

    I did some more testing without a load but with a beefy power supply in constant current mode (the source be the load!) now. 6.4A through the 0.05 Ohm shunt is working beautifully for extended periods of time. The shunt gets to 82degC, so some active cooling with forced air is probably on order.

    Here is a plot of test results, that show tolerances <2% across the range. Measurements below 200 uA are getting inaccurate. In general, tolerance increases at the lower end of every range, which means more noise at lower voltages across the current shunt. 

    More numbers and graphs to follow. And I need a different load to bridge the gap between 60 and 100 mA.

  • Read the datasheet ...

    MagicWolfi11/18/2019 at 18:00 0 comments

    ... always. 

    During testing I noticed a significant difference between measured and expected current values. "Well hidden" in the datasheet (page 3 Electrical characteristics) is this line:

    Vin- is the culprit here: Basically the part has a pull-down resistor connected to its negative measuring input pin! Really? This 'feature' draws 3.125uA typical per volt of bus voltage, which messes up low current measurements. And this is only a typical value. Every part has to be tested to find its real value. 

    This is one of the reasons, I decided to change the low current shunt resistor from 500 Ohm to 5 Ohm and bury my dream of measuring nA with this device. 

    On a side note: The widely popular INA219 has the exact same issue.

  • Current testing

    MagicWolfi09/24/2019 at 18:03 0 comments

    The board survived 4.95 A through the 0.05 Ohm shunt and test jig 0.5 Ohm resistor for > 1 minute. The shunt did not get too hot. My index finger temperature probe stayed rare.

     The 5 W power resistor on the test jig got too warm to touch, so some forced air cooling will be required for longer tests. Or a bigger resistor to handle the 12.5 W. 

    Todo: Getting a log of the measured data from the INA209 and more testing to follow.


    with 0.05 Ohm Shunt

    Multimeter Verification

    Fluke 179

    0.5 Ohm
    4983.4 mA
    5.0 A

    193.2 mA0.194 A99.6%

    5.271 A5.29 A99.6%
    2 Ohm220.6 mA222.1 mA99.3%

    400.9 mA399.4 mA99.6%
    110 Ohm
    52.4 mA
    50.0 mA95.4%
    25.6 mA
    25.0 mA97.7%
    9.8 mA
    10.01 mA97.9%
    4.2 mA
    5.01 mA83.0%

  • Test Jig 2

    MagicWolfi09/16/2019 at 23:52 0 comments

    I built another test jig, this one to exercise the business end of the Watt-A-Live. It has a barrel connector to adapt to an external power supply and a selection of 5 load resistors for different current settings.

    The resistor values are 0.5 Ohm, 2 Ohm, 110 Ohm, 12 kOhm and 10 MOhm (still missing :( ) for a full range of current settings. They can all be selected by jumpers.
    This is how it looks, when plugged into the shield/wing.

  • Rev2 boards

    MagicWolfi08/02/2019 at 01:51 0 comments

    Rev2 boards have arrived. They are SMD assembled by Elecrow. Quality is excellent as usual. They are labeled rev 2.1 for tracking purpose as I had to make a small change after the quote with the 2.0 data files.

    Differences in a nutshell:

    • Boards a longer to give access to the bypass jumper when a Feather is plugged in from the top.
    • Shunt have an improve power rating.
    • The high current range shunt is now 50mOhm to give a current range from 6.4A to 200uA.
    • Banana jacks have a solder tab on the bottom for a lower resistance connection.

    And this is how to board looks like with SMD components only:

  • Test jig

    MagicWolfi07/31/2019 at 15:39 0 comments

    I built a test jig, which turned out to be a universal jig for Arduino Uno form factor PCBs without headers (when all pins are populated). 

    I ordered PCBAs with SMD components only to save cost and be able to customize for Arduino or Feather headers. To test the boards without adding connectors the jig comes into play. I used an old shield PCB and drilled out the holes to fit 1mm pogo pins. The pins soldered into IC socket rows and stuck through the PCB r proper alignment. Now I can stick the jig into an Arduino and place the shield to be tested on top and press down.

    A mechanical test fixture to clamp down the board stack would be helpful, but for now it is only 25 boards to test. No really mass production yet. A crude clamp manually attached helps for longer test runs for now. 

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