I bought a 1.8-inch seven-segment common cathode LED display from AliExpress. So no datasheet available.
I used a 1 kΩ resistor and a 5 V source, as to put a max 5 mA in the LED. I measured 1.6 V for the decimal dot, and 3.5 V for each segment. The measured current draw for one segment was 1.5 mA.
Now, I expected each LED to be quite dim at 1.5 mA, but it was the opposite, I could put a 4 kΩ resistor and still has a usable display.
I intended to drive the display using an ATmega328P and a MAX7219 (which would have been OK up to 500 mA per segment).
Does this measurement seem correct, and if so, I can drop the MAX7219 and drive the segment directly (with current limiting resistors) with the ATmega?