INA219 — current, voltage and power¶
Being prepared
Chosen for the catalogue; the driver has not shipped yet. The figures below still need checking against the datasheet.
What it does¶
Watches a supply rail and reports how much current is going down it, what the voltage is, and therefore the power. It measures across a shunt resistor on the high side, so the load keeps a solid ground — which is what you want when the load is a motor, a heater or a whole subsystem you are trying to account for.
Typical use: knowing that a machine draws what it should, and noticing the morning it starts drawing more.
Parameters¶
| Measures | Current, bus voltage, power |
| Bus voltage range | 0 … 26 V |
| Converter | 12 bits |
| Interface | I²C |
Bus and addressing¶
I²C, 0x40–0x4F, chosen by two address pins. Sixteen possible addresses, which is more than the bus will comfortably carry.
Wiring¶
The shunt goes in series with the rail being measured, not across it. The breakout boards come with a shunt already fitted; the value of that resistor decides the current range and the resolution together.
In a project¶
To be written.
Traps¶
| Trap | What to do |
|---|---|
| Wiring the shunt across the rail instead of in series | This is a short circuit. Read the diagram before powering anything. |
| Measuring a rail above the part's limit | The bus voltage input has a ceiling. A 48 V system needs a different part, not a hopeful one. |
| Expecting to catch a startup surge | The converter takes its time. It reports a steady draw well and a millisecond spike not at all. |