I am currently using BC 547 transistor and an Arduino Uno to turn a low power switch on and off. I have successfully achieved this with one of the Arduino output pins, but would like to replicate this over 13 of the pins. This would require 13 transistors and resistors, one for each pin, which seems like overkill. I want to know if there is a neater way of doing this with an IC?
The ULN2003 Arrary contains 7 darlington transistors connected with common emitter.
There is even a base resistor included. You could choose which voltage level you desire, such as ULN2002, 2003 or 2004
EDIT #1 : as pointed out by Peter Green, the saturation voltage (Collector to emitter voltage) when transistor is on is higher with Darlington than with a single transistor. Where typical transistor saturation voltage might be 0.3 to 0.8 volts. The ULN2003 saturation voltage can be from 1.1 volts to 1.6 volts. Resulting in significantly more power dissipation of a single transistor.
You are looking for the ULN2003, High-Voltage, High-Current Darlington Transistor Arrays.
Fiugre 1. ULN2003.
The base resistors and snubber diodes are even built-in!