INA226 is a microchip from Texas Instruments that can measure current and voltage and calculate power from it. It is often used to monitor power consumption or the yield from solar generators.
INA226 is available as ready-to-go breakout board with an integrated Shunt and should cost less than EUR 2/piece.
INA226 internally uses a 16-bit ADC (Analog-To-Digital converter) to measure voltage. It uses the Shunt principle to measure current via measuring the voltage drop at a Shunt resistor.
The maximum measured voltage is 36V. The maximum measured current depends on the value of the Shunt.
Because of its high-resolution 16-bit ADC and automatic internal averaging of multiple samples, it produces very accurate and reliable readings. All of its measured and calculated values can be read by a microcontroller via I2C.
Shunt Value and Maximum Current
INA226 does not measure current directly. Instead, it measures the voltage drop at a Shunt resistor. The resistance of the Shunt determines the maximum current that you can measure.
Integrated Shunts
When using breakout boards, the most common presoldered Shunt is R100 (0.1 Ohm). In theory, this enables the breakout board to measure a maximum current of 0.8A.
Less often you find boards with a R010 Shunt (0.01 Ohm) which increases the maximum current to 8A at the expense of precision. Boards with a R002 Shunt can measure up to 20A.
The real maximum current that you can measure with this type of breakout board depends on two factors:
- Overall resistance: In addition to the resistance of the soldered Shunt, there can be more resistances adding up. Cheap breakout boards use PCBs that add additional resistance in their paths. Likely, the overall resistance is higher than expected.
- Conductance: A small PCB cannot conduct high currents. Since the Shunt is connected in series with the load, the full total currency is flowing through it. The practical maximum current - regardless of Shunt - is most likely limited to 5-8A, depending on PCB quality.
Always test and measure breakout boards with integrated Shunts yourself and individually board-by-board to find out their true maximum current.
Should the breakout board max out even on low currents (indicating that the Shunt resistance is too high), you can try and short circuit the integrated Shunt resistor. Often, the low-quality internal resistance of the PCB all by itself is acting well enough as a Shunt.
If you need to measure larger currents, consider removing the presoldered Shunt and connecting an external Shunt rated for higher currents.
Pin Layout
Typical INA226 breakout boards come with 8 pins:
| Pin Label | Description |
|---|---|
| IN+ | Positive Voltage for Load Circuit |
| IN- | Negative Voltage for Load Circuit |
| VBS | Bus Voltage |
| ALE | Alert |
| SDA | I2C SDA |
| SCL | I2C SCL |
| GND | Common GND |
| VCC | 3.3V/5V supply for INA226 |
- VCC and GND supply the breakout board with the power it needs to operate. Both 3.3V and 5V are supported.
- SDA and SCL are the typical I2C pins used to communicate measured values to a microcontroller.
How to Connect a Load
To measure voltage and current, you typically need four probes: two wires to the positive and negative pole of the power supply to measure the voltage, and two wires the cut the circuit to insert the Shunt and connect it in series. In reality, you just need three probes because depending on whether you measure on the high (positive) or low (negative) side, two probes will either both be GND or V+.
To translate this to the INA226 breakout board, it is important to understand how it measures the voltage: in addition the voltage drop across the Shunt, it measures the voltage drop across the load. By summing up both, the total voltage is calculated.
The four probes (pins) involved in current and voltage measuring for the INA226 look like this:
This helps understanding how the external circuit that you want to measure needs to be connected to the breakout board:
- The load needs to be connected to VBS and GND
- The Power Source for the load needs to be connected to VIN+ and GND
As outlined above, in reality for combined current and voltage measurements, only three probes (pins) are needed. In this high side setup, VIN+ and VBS are connected to the same spot and can be combined.
Here is the complete circuit for a high side setup (measuring the current on the positive side of the load):
Examples
Here are available example sketches:
- Basic Setup: Setting up a INA226 breakout board with an ESP8266 microcontroller to perform voltage and current measurements. Includes necessary library and complete platform.io project.
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(content created Feb 27, 2024)