I am trying to design a basic project to multiplex a 3x3 LED grid in a common anode arrangement. In order to avoid sinking (sourcing?) too much current from the digital I/O pins I would like to uses NPN transistors as a low-side switch for each column.
I understand the case where I use a transistor to switch a single LED with the anode connected to Vs. However, I am having difficulty in designing the circuit for the multiplexed approach.
As my circuit stand I can’t understand how to to wire it to source current from Vs and using I/O to control the flow.