Follow me down the optimization rabbit hole

Those little OLED displays are everywhere, and there's a good reason. They're inexpensive, easy to program and they look good. I wanted to explore how much current they draw so that I can plan better for battery powered projects. Questions I want answered: How much idle current is drawn when the controller is off versus on (blank display)? What's the minimum current to see text indoors? What's the maximum current when all pixels are on at their brightest? How does display size affect current draw? How does active data writing affect current draw? It's obvious they use more, but how much current do grayscale and color OLEDs use? How practical are OLED displays compared to common LCDs for battery powered projects? Materials: Cheap multimeter (manual scale, assumed accuracy +/-10% at worst) Various OLED displays (72x40, 96x16, 128x32, 64x32, 128x64-0.96", 128x64-1.3") Arduino compatible microcontroller ( Adafruit nRF52840 Feather Express ) ...

The Premise So, you've created an Arduino project and you want to power it with batteries to take it on the road. Your board's components are designed to run on 5 Volts and you know you can't feed 9V directly into the Vcc of a 5V board because it will damage it. Arduino has you covered - the pin marked "RAW" is for that purpose and according to the documentation, you can feed it between 6 and 12V and it will regulate that voltage down to the 5V needed by the board. Perfect, right? Well, not quite. Voltage Regulation There are 2 main ways to regulate (aka control) the voltage. A linear regulator allows you to supply a higher voltage than desired (in our case 9V) and get a stable, lower voltage as output. It essentially does this by generating heat from the excess energy. Let's say your board uses 100mA @5V while executing your code. If you're powering it from a 9V battery through a linear regulator, then you're creating 4V x 100mA = 400mW of waste...