Once I had ESPHome set up and running, the software side of creating a small wireless voltage and current sensor node with was super easy. I needed to copy sample code for I2C bus component, then sample code for INA219 component, and... that's it. I started getting voltage, current, and power reports into my Home Assistant dashboard. I am impressed.

It was certainly far less work than the hardware side, which took a bit of soldering. I started with the three modules. From left to right: the INA219 DC sensor board, the MP1584EN DC voltage buck converter, and the ESP8266 in a Wemos D1 Mini form factor.

First the D1 Mini received a small jumper wire connecting D0 to RST, this gives me to option to play with deep sleep.

The MP1584EN was adjusted to output 3.3 volts, then its output was wired directly to the D1 Mini's 3V3 pin. A small piece of plastic cut from an expired credit card separated them.

The INA219 board was then wired in a similar manner on the other side of D1 mini, with another piece of plastic separating them. For I2C wires I used a white wire for SDA and green wire for SCL lines following Adafruit precedence. Vcc connected to the 3.3V output of MP1584EN in parallel with D1 mini, and ground wires across all three boards. The voltage input for MP1584EN was tapped from Vin- pin of the INA219 board. This means the power consumed by ESP8266 would be included in INA219's measurements.

A small segment of transparent heat shrink tube packed them all together into a very compact package.

I like the concept of packing everything tightly but I'm squeamish about my particular execution. Some of the wires were a tiny bit longer than they needed to be, and the shrink tube compressed and contorted them to fit. If I do this again, I should plan out wire my lengths for a proper fit.

Like I said earlier, the hardware took far more time than the software, which thanks to ESPHome became a trivial bit of work. I was soon staring at a flood of data, but thankfully ESPHome offers sensor filters to deal with that, too.