So basically what we will do is connect out smartphone to a bluetooth module. This buletooth module is connected to the Arduino using a UART connection. We send text to the Arduino and this will display that text to a huge 8x32 1cm LED matrix. We will learn how to build that LED matrix using 256 LEDs, 4 MAX7219 matrix drivers and one arduino. So let's get started.

Material

1 x Arduino (NANO or UNO)

1 x Bluetooth module HC-06

256 LEDs (I've used 10mm)

4 x MAX7219 LED matrix drivers

2 x 100x40 cm wood board

1 x ams1117 5V voltage regulator

1 x 10uF capacitor

1 x 100nF capacitor

1 x 12V transformer

Drilled PCB, connectors, solder, wires, tools, etc...

Schematic -Arduino UNO

We have to create 4 matrices eacho of 8 by 8 leds. Each MAX7219 driver can handle a 64 LEDs matrix. The arduino will send the data using a serial comunication. So we have to connect the clock and load pins from the arduino to all MAX7219 drivers. The data pin will be only connected to the first driver. From the "data out" pin of the first driver we will connect a wire to the second "data in" of the second driver and so on. That's how we connect four 8x8 matrices in serie. We should also connect the bluetooth module to the Tx and Rx pins of the arduino and supply 5V to it and to each of the MAX7219 drivers.

First let's take a look on how to connect each of the 8x8 martices. Once we have our 4 matrices we can join them together with the "data out" "data in" pins.

In the above schematic you can see how to join one 8by8 LED matrix. We have to create 4 matrices in the same way. Once we have our 4 matrices we connect the data out from the first to the next data in and so on. The load and clock is the same for all matrices. As you can see in the schematic above, it shows the back view. The arrow shows the direction of the next 8by8 module. You can see the final circuit in the schematic below.

In order to not get lost, let's take a look at the fron side of the entire 32by8 matrix in the picture below. You can see that now the arrow pints the oposite way than in the previous modulke scheamtic. That's because we've flipped the modules and we can see the front side. So the text will scroll from right to left, from the first 8 by 8 matrix to the forth one.

The App

Ok, so to send text to our huge LED matrix we have to establish a bluetooth connection between our Android smartphone and the arduino. For that I've created the next App using App inventor. If you want to learn how to create your own Arduino App just watch my video. The next app has one button for bluetooth connectiom, one text box and a button to send the text.

You can download this app from the link below. Copy the apk file to your smartphone using a USB connection or just download the App directly to your phone. You have to enable unknown origin aplication to be installed to your smartphone in order to be able to isntall this App. For that go to settings, security and check the unknown origin block.

Before we open the App we have to syncronise the bluetooth module. For that go to bluetooth setings on your smartphone and search for devices. When found, select the hc06 module and use the 0000 or 1234 passwrod to syncronise. We're done. Now open the app. Click the bluetooth icon and select the hc-06 module. Type your text and send.

Schematic ATmega328

We've seen the schematic for an Arduino UNO. But I want to use the ATmega328 chip directly on to a PCB. For taht we have to add the chip and all the extra components that make the microcontroller work such as the crystal oscilator and the oscilating capacitors. Also we have to add a 5V voltage regulator.

As voltage regulator I've used the AMS1117 5V voltage regulator with two capacitors to filter the noise. We add 6 female pins for the FTDI module. Add a 0.1uF cap between DTR and reset pin of the ATMEGA328. Connect the RX and TX pins for the bluetooth module as well. Add 4 female pins for this as well. Connect the Data, clk and load pins to the MAX7219 driver. Connect the first driver to the first 8x8 matrix and the Data out pin to the next driver and so on.

Programming the ATmega328

If you use the Arduino UNO or NANO just download the code below and upload it to the Arduino. Remember to disconnect the Tx and Rx pins from the bluetooth module while uploading the code.

If you use this same ATmega328 on a PCB you have to make sure that it already has a BOOTLOADER burned to it. If you want to see how to burn a bootloader to an ATmega chip just check my next video.

Now that the atmega chip has the bootloader we can upload the code using the FTDI module. Connect the FTDI as shown in the schematic above. Open Arduino IDE and open the next code:

The code:

Create unique symbols

To create unique symblols just search the vectors for the letter that you want to change. For example I want to display a smiley face every time I send a underline (_). For that I go to the underline symbol commented as (//_) and add the "1" in such a way that it will display some sort of smiley face.