I have a circuit which is turned on at a logical zero. I would like to have a LED indicating this circuit is on, but I only have NPN transistors at this moment, which conduct when there's a logical one on its base.
Is there a way to "emulate" the behavior - i.e. that when there's a logical one, the LED isn't lit up, and when there's a logical zero, the LED is lit up - without having to use a PNP transistor?