LCD displays with serial input can be upgraded to Bluetooth using a JY-MCU Bluetooth Serial Port. A good reason to do this is so the display can be used with an Android phone or tablet. A simple Android application created using the MIT App Inventor can send strings to display on the LCD screen.
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Step 1: Parts
LCD display with TTL serial input
In this example, the Adafruit 16x2 RGB back light LCD with USB + Serial backpack is used but there are many similar displays. Sparkfun also has a large collection of LCD displays with serial input. Warning: A plain LCD display will not work because it does not have serial input. The serial input is usually an additional board sometimes called a backpack. Displays with I2C or SPI serial will not work. Be sure it has a UART serial interface.
JY-MCU Bluetooth Serial Port
This device adds Bluetooth to any device with TTL UART serial interface. This is available from many sources including Amazon and eBay.
Step 2: Connection
On the back of the display identify 5V output, ground (GND), and serial receive (RX) signals. On the JY-MCU identify the 5V input, ground (GND), and serial transmit (TX) signals. The goal is to connect LCD-5V to JY-MCU-5V, LCD-GND to JY-MCU-GND, and LCD-RX to JY-MCU-TX.
I used a cable included with the JY_MCU and cut off one end. Next strip off some insulation from three wires then solder the wires as shown in the picture.
The display needs 5V so plug in an old phone charger or similar to the USB port. It is not necessary to plug the LCD into a computer because it receives data over Bluetooth, not USB.
Step 3: Try It
Use the Android Bluetooth settings to pair with the JY-MCU. The PIN code is "1234"
Download Bluetooth Terminal by Qwerty from the Google Play store. Connect to the Bluetooth device "HC-06". Send a string and see it displayed on the LCD screen.
When finished be sure to close the application so it does not interfere with the next step.
Step 4: Send Text From an Android Application to the BT LCD
The MIT App Inventor website can be used to create Android applications using many features including Bluetooth. Sign up, then import the attached file BlueT.aia. This application is not written in Java so there is no source code in the usual sense. MIT AI2 applications are created in a visual programming language so they can only be viewed on the website.
The application consists of 3 buttons. Press the "Select BT Device" button then select the "HC-06" device. Press the Hello button. The LCD screen should show "Hello world". Now press the Bluetooth button. The LCD screen should erase the previous message and show "Bluetooth". It is very easy to modify the application to send whatever strings you wish and to add new buttons.
See the attached video for step-by-step instruction on building MIT AI2 Bluetooth applications. The application in the video uses the HC-06 is a different way but most of it applies to any Bluetooth application.
This is not my video so give all props to the video author.
Step 5: Display Commands
Every LCD display has special commands to clear the screen, change the back light, etc. Be sure to read the display documentation. In this case, the display clear screen command is the number 254 followed by the number 88.
The picture shows how MIT AI2 sends the clear screen command before sending the string to display. The picture shows a fragment of the BlueT application for button1 (Hello). When button1 is pressed, the numbers 254 and 88 are sent to clear the screen. The next step it to send the string "Hello world".
Step 6: Final Thoughts
Find a source of interesting text messages to send to the display. For example, MIT AI2 can access Twitter. See the Designer Social palette.
Another possibility to is use the Web option on the Connectivity palette. It might be possible to get weather alerts, traffic alerts, top headlines, etc.