I ordered a few ULN2002As.
I have it wired as follows:
Pin 1 -> GPIO of Arduino Pro Mini 3.3V
Pin 16 -> 300Ω resistor in series with an LED
Pin 8 -> GND
Pin 9 (COM) -> 5V (which is also RAW for the Arduino).
Pins 1-4 were wired similarly with LEDs but I've removed 2-4 because it wasn't working and testing with 1 was simpler.
When I apply 3.3V from the GPIO to Pin 1, nothing happens. When I disconnect GPIO and just apply 3.3V with a jumper, nothing happens. If I apply 5V, nothing happens. The output just swings around 300mV.
Am I totally misunderstanding how this chip works? I thought applying at least Von (2V according to the datasheet) at Pin 1 should make Pin 16 turn on.