Datasheets, simulations, and good ol’ fashioned math can help us make predictions about power consumption or production, but the real world doesn’t care about any of that and the only way to get trustworthy numbers is to collect actual measurements. However, that can be tricky — especially if the system in question is in a place where you don’t want to sit with a multimeter for hours or weeks on end. That’s why Adrian designed this DIY device to help people monitor and log DC power flow.
While collecting real power data is a problem that Adrian has faced many times, it became particularly apparent while he was working on his WINTURER portable battery-charging wind turbine project. The whole point of that project was to generate power, so data was critical in helping Adrian optimize the design. Adrian developed this device to collect that data and is sharing the design with the world so anyone can use it when working on their own projects.
This energy meter operates in a very simple way: just connect it in line with the load. It will measure voltage and current, which it can then use to calculate power in real-time and power over time. It shows that information on a small screen on the device itself, but also uploads it to a Blynk cloud IoT dashboard for logging. There are different options for connecting to Blynk’s online servers, including WiFi and a cellular modem.
The heart of the device is a Wemos D1 Mini-style ESP8266 development board. That takes power measurements using an Adafruit INA219 module and shows the results on an Adafruit SSD1306 OLED screen. Those components solder onto a custom through-hole PCB and fit inside a 3D-printed enclosure and Adrian provides two versions to suit user needs. The first includes a space for a small power bank with an 18650 lithium battery cell. The second doesn’t and is meant to be used with a wall wart power supply or a large power bank for long term monitoring.
In either case, Blynk’s free plan should be enough for data from one energy meter — though there are paid plans if you require additional resources.
