A 6.4A-2uA current/voltage/power monitor based on the TI INA209
with dedicated GND, usable as Shield, Wing, Breakout or Breadboard.
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. 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 2µA
- Realistically the overall range is 6.4A to 1mA measured or down to 200µA calibrated with ~2% error
- Positive and negative current flow
- Bus voltage 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 bypass
- Rev 2 Size: 71mm x 54mm (2.8" x 2.1")
This board is for sale in my Tindie Store.
Software library and design files are available on my Github page. Updates are happening slowly.
High Current Testing
The board survives 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.
Testing without a load and 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. I need a different load to bridge the gap between 60 and 100 mA.
|Shunt||Measurement||Multimeter Verification Fluke 179||Acuuuracy|
|0.05 Ohm||4983.4 mA||5.00 A||99.7%|
|2.0 Ohm||220.6 mA||222.1 mA||99.3%|