In this earlier post, we designed a schematic and PCB for our 8×8 LED matrix and didn’t really pay attention to the data sheet. Like a bunch of idiots, we just assumed that the pins along one edge were for the “rows” and the other set of pins were for “columns”.

So it’s no wonder that by sticking voltage across the pins resulting in some really peculiar behaviour. Where we expected the top-left corner LED to come on, one somewhere in the middle near the bottom lit up! The next pin along didn’t light the next LED in the row, but one about three places along.

To get the top-left LED to light, we don’t simply put power onto the first pin at the top, and ground the first pin on the bottom set – that won’t actually light any LED!
Assuming our pins are labelled 1-8 across the top, and 9-16 along the bottom, connecting power to pin 1 and ground to pin 9 doesn’t pass through any of the LEDs. If we put power onto pin 1, we need to ground one of either pins 3,4,6,11,13,15 or 16.

With this in mind, we’ve had to re-draw our schematic (and make a new PCB using a similar layout):