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red 8x8 matrix with 26 pins? Answered

I received this matrix in the mail and I'm having problems trying to get it wired, as you can see it's it has 26 pins, the schematic has 8 pins for the rows and 8 pins for the columns but the other 10 are sitting at the bottom with the words "no pin"? I tried to wire up the rows and columns but had no success.

My main goal was to have it hooked up to a couple 74HC595 shift registers (via 16 pins?) on some protoboard. Any help on how to get this wired would be appreciated!



8 years ago

wow, thanks for the fast responses Frollard and Alex!

I hooked up the pins to 23 and 11 and it works, I'll try the whole thing again later. I guess I should of noted that this is being hooked up to an arduino.

one more question:

On matrices how do you know where to put the resistors ie. anode/cathode, row column. In this case I'm assuming you add them to the anode mainly because it's one colour and I have the chance to, but on RGB (common anode) you see them on the cathodes. I thought you always need to put the resistors on the positive side?

go easy on me I'm new to this :)


Answer 8 years ago

it doesn't matter if you put the resistors on the anode or cathode.

The reason why you see them put on the cathodes of an RGB common anode LED is because when you put LEDs in parallel, each LED should have it's own resistor.  LEDs arn't made perfectly, and some have slightly lower voltage drops than other, so they turn on easier.  Lets say you put 10 LEDs in parallel with only one resistor and lets say we want 20 mA each.  If one of those LEDs hogs up all ofthe current (worst case:100mA), then it'll instantly burn out.  This then gives the remaining LEDs more current, and if the same thing happens again (another LED takes on the full 100mA) it'll surely blow, giving the remaining LEDs 33mA each.  This can burn out the LEDs and then boom, they're all dead.  It's a spectacular chain effect.

Anywho, going back to the RGB LED, since all it really is is 3 LEDs in one package with all of there anodes together, if you put the resistor on the anode, then the problem stated above can occur.

Also, in an RGB LED different colors have different voltage drops, usually:
red: 1.7v
green: 2.1v
blue: 3v

so if you were to put the resistor on the anode, the red would blow, then the green, then the blue.

In short:
anode or cathode, it doesn't matter where you put the resistor.
if you have LEDs in parallel, make sure each LED has it's own resistor (or if you have a bunch of sets of series LEDs in parallel, make sure each series set has it's own resistor)
on common anode RGB LEDs, each cathode needs it's own resistor
on common cathode RGB LEDs, each anode needs its own resistor


Answer 8 years ago

By convention, one applies a resistor to the high side of an LED, but it's not imperative, and it's not always possible. The resistor simply serves to limit the current, so it can technically be placed on either side.


8 years ago

1. make sure you have the right polarity
2. make sure you have the right voltage

test by just connecting one row driver with one column driver to power - see if any of the leds lights.

all the 'not connect' pins are usually there for support to solder to a pcb.

Side note:  To use the 595 chips you'll need a transistor array to either source or sink one-or -the-other rows or columns because the 595's will only source, or sink themselves...I forget which.


8 years ago

look at schematic:

put power to pin 23, and 11, the top right led will light up

the "no pin" are not connected to anything