I am trying to prep my wiring for a 8x8 Led Matrix w/ Bluetooth according to the following instructable:


Instead of soldering everything together I'd much rather use a breadboard. I'm new to wiring, breadboards, and Arduino's in general. I was wondering if anyone could look over my sketch and see that the connections I've made are valid.

I'm basing my wiring off this image (See original instructable for higher resolution): enter image description here

I realize the bluetooth module isn't the same. I'm just using this as a reference. The wires leading off the top of the board will be going to the LED Driver module.

EDIT: Thanks for the feedback guys. I have decided to go with the Innogear HC-05 module. I've adjusted the wiring according to that model. As per the suggestions, I've switched my power and ground rail and eliminated the resistors and ground for TX communication. (I've still kept a ground for the BT). Here's my new attempt: enter image description here

  • I realize that it's not your fault, but a voltage divider is a terrible level shifter. Also, are you sure you're using a 3.3V Bluetooth module? Jul 25, 2014 at 3:22
  • Sorry, I'm not sure what a voltage divider is. As I said I'm very new to all this. As for the BT module I plan on using the HC-05, just showing the RN-42 for reference (Power should be coming off the 5V rail). I'm open to any suggestions, and I'm certain this isn't laid out as efficiently as it should be. Jul 25, 2014 at 3:37
  • Which specific Bluetooth module are you using? The one in the top image is not a bare HC-05. Jul 25, 2014 at 4:28
  • Planning to pick this one up soon. amazon.com/Arduino-Wireless-Bluetooth-Transceiver-Module/dp/… Jul 25, 2014 at 7:50
  • Looks the same as the original so it's good. Except pin53 should have had a green wire instead of a white. Good luck.
    – Gerben
    Jul 25, 2014 at 14:12

2 Answers 2


I am the author for the Instructable ethanx94's wiring is based on. It seems like the active and helpful members here have already helped iron things out.

If anyone is using the Arduino sketch downloaded from my instructable but is using ethanx94's wiring, do remember to change the SPI SS (Slave Select) pin in the sketch from 10 to 53 to reflect the correct pin used.

Look for the following line in the sketch and change the pin number 10 to 53:

int SPI_CS = 10;// This SPI Chip Select pin controls the MAX7219
int SPI_CS = 53;// This SPI Chip Select pin controls the MAX7219
  • 1
    Welcome to Arduino SE! It's cool that the author of the tutorial is commenting on a question as that doesn't happen much. Feel free to stick around and ask/answer other questions... One note is what about pins 11-13/50-52? Do those need to be remapped in the code, too? (Arduino documentation: arduino.cc/en/Reference/SPI) Jul 26, 2014 at 22:10
  • Sorry for late reply. I am not active here. There is no need to remap the other pins in the sketch downloaded from my instructable except the SPI SS pin.
    – Nick Lim
    Jul 31, 2014 at 23:57

Those are, in fact, the same board. When you look at this image (from Amazon)...

...you can see that there are really six pins, just two of them aren't soldered.

Your circuit:

  • On the power rails, you have the 5V and ground switched. It'll work okay, but you're asking for trouble later on when trying to work with it and accidentally plugging a wire into the wrong rail.
  • Also, from the reviews on Amazon, it says that it can be powered with 5V since the breakout board provides voltage conversion. However, no one specifically mentions the TX/RX, so I'd not risk it. This module (seems to be same chip) costs less and a reviewer specifically says that it converts voltage for both power and the TX/RX.
    • I'm not going to verify the resistor values, since you don't seem to need them if you get the other module I listed.
    • If you still did want to do the 5V/3.3V conversion, you should connect the power wire to the 3.3V pin, not the 5V rail on the breadboard

tl;dr: it seems as you just need to skip the resistors for the yellow wire and make a direction connection. I'm not 100% sure about that specific part but there was another one that a reviewer specified that this was okay.

Note: I cannot comment on the other wires for the shields, but at a quick glance it looks good.

  • Thanks so much for the feedback. I've updated the OP accordingly, as well as cleaned up the overall shape of things. Jul 25, 2014 at 22:10

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