The USBmicro U421 USB interface can drive one or two low-current LEDs directly. But several of the LEDs I chose are not low current, and using a driver to pump a little more current through the LEDs will make the bright ones very visible from way over in my lab. The U421 provides 5V from the USB port. In the photo below the U421 was mounted on the PCB along with the ULN2803. Resistors will be mounted and connections will be made on the bottom of the board.