I've got a bunch of 7 segment displays which i'd like to control with an arduino mega2560.
I've been reading up on using a ULN2003 which seems like my best option. However, I've noticed quite a few people saying that i will require an external power supply for this. This seems odd to me as the 7SD's are essentially just made up of LED's which can be powered easily by arduino. In fact I have already powered single segments up via a current limiting resistor using the onboard 5v supply and they worked fine.
Is it really necessary to use an external supply? This is important to me as my ultimate goal is to incorporate them into a device which uses the Hiduino bootloader on the 16u2 and thus is powered soley via USB connection to the arduino. I am not really up for adding an external power supply to this particular device as it works nicely as a compliant HID.
I am contemplating using an LCD unit instead which would make things a lot easier but seeing as I already have these 7SD's I would really like to use them if i can.