This is a simple current meter based on the ESP-12E, LTC-4150 and SSD1306 OLED module. It lets you measure the average current draw of a circuit with variable load accurately.
The current meter is powered by the micro-USB port on the ESP-12E. You plug the source battery into the "IN" terminals on the LTC-4150, plug the circuit to measured into the "OUT" terminals on same, then press the RST button on the ESP-12E to start measuring the current draw.
The OLED screen will show the elapsed time and the average current draw in mA.