powering 7 segment displays

Hi,
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.

Thanks

Start by giving information!

Show the Web page specifying them.

Why would you want to use a ULN2003?

The proper way to operate them is to use a MAX7219.

sorry it appears i was reading nonsense. I have since found a few things saying it should be able to power them fine.

I've just done a quite search on the MAX7219 and found that it is serially interfaced. Will this be okay if i'm using the hiduino bootloader 16u2 as I'll be using MIDI.begin as opposed to Serial.begin. Or can i just use them both?

Thanks

liamorourke:
sorry it appears i was reading nonsense. I have since found a few things saying it should be able to power them fine.

I've just done a quite search on the MAX7219 and found that it is serially interfaced. Will this be okay if i'm using the hiduino bootloader 16u2 as I'll be using MIDI.begin as opposed to Serial.begin. Or can i just use them both?

Thanks

Wrong, wrong, totally wrong. You seem to be searching in all the wrong places. :slight_smile: You don't interface to the MAX7219 with asynchronous serial like the hardware serial ports on the Arduino. So neither of those will work. But almost any other pins can be used, including the SPI pins. You need to install and reference an appropriate library to drive it, like LedControl.