The BV4338 is an LCD charter display controller that will attach to LCD displays with a HD44780 controller or similar. It has a Bluetooth interface that work with a VT100 type protocol and so is very easy to use.

Circuit Diagram

Bv4338 sch.jpg
Click to enlarge

The following may be needed

  • BV COMM version 2 this has a useful script facility
  • script for testing the VT100 commands
  • script for setting up Bluetooth
  • Data zip file contains AT commands and module detail

Getting Started

The BV4338 is an LCD controller that uses Bluetooth as the method of communication instead of connecting directly to a serial interface.

BV4335 numbered.gif

  1. LCD Connector
  2. Alternative LCD connector
  3. Contrast
  4. Power in
  5. Power in via 2.1mm connector
  6. 5V regulator for the LCD
  7. 3.3V regulator for the Bluetooth
  8. Indicator LED's
  9. Bluetooth module

Connection to the LCD is fully covered in the data sheet and so it is assumed that it is already connected. The 2.1mm power input socket (5) can take up to 12V which can be AC or DC. The connector to the right of this (4) must be DC and must be connected the right way round. This can take up to 18V DC. On first connection the screen should look something like:
BV4338 signon.jpg
This is connected to a 20x4 screen but will work well with screens of most sizes. when first switched on the IND LED will be flashing rapidly, this indicates that the device is ready to be discovered. For this example I am going to use a Bluetooth dongle connected to the PC and Bluesoleil software which seems to be popular.

Clicking on the orange ball in the middle has relieved our device which in this case is called "OmniTek_Bluetooth". This may be different and later on if you have a BV103 this can be changed.

Bluesoleil 1.jpg
Double clicking on the device will reveal a yellow box round the Bluetooth serial port service, right click on the device name and select connect. I got a dialog box
Bluesoleil 2.jpg
that told me that the COM port was COM 4, selecting either Yes or No established the connection and the PR LED illuminated on the BV4338.

Time to Talk

Now there is a connection established use BV COMM version 2 as this has a handy script utility. Set BV_COM2 as shown although your COM port may be different. On the serial menu switch Echo OFF - i.e. unchecked.
BV4338 com2 1.jpg
9600 is the default Baud rate that the Blue tooth device works at and also the BV4338 has been fixed initially to this. The display is also set to 16x2 even though we are using a 20x4 display, we can fix this later. Notice in the picture there is a [02]* before "hello World". This was achieved by sending byte value 2 which is control B on the keyboard. Do this until there is an ACK (*) from the BV4338. Some Bluetooth devices go to sleep after a while and it is possible to miss the first letter although the dongle connected to this PC has not shown this problem.

Whatever you type into the terminal should now appear on the screen, its is also being echoed back by the BV4335 so that if the connection is dropped or is out of range there will be noting appears on the terminal, this is a big advantage of having a transceiver at the salve end.


There is a ready made script file that has most of the VT100 commands to save you looking them up, this can be opened by the script dialog in BV-COM2. Download the script file unzip it and open it using the script dialog box.

BV4338 scripts.jpg
You can add to this or delete from it. There is no CR after the command on V100 commands, if you do put a CR on then the cursor will move down one which is not always what is expected. Try the Clear screen and home cursor command by selecting it and pressing Send. For this display there is a script "Set to 20x4 and save to EEPROM" that i shall use for this display. The display may need a reset (escc) after this.


It is possible to access the AT command interpreter of the Bluetooth module and change the name and Baud rate. For this you will need a BV103 or similar to communicate with the Bluetooth module.

BV4338 BV101.jpg
The Bluetooth module uses 3.3V logic but is tolerant at the input to 5V, it is better to use the BV103 on the 3.3V setting but 5V will do, thus a BV101 could be used. The BV103 will also power the Bluetooth module. Only 4 wires are needed, a power supply shown by the red and green lines. This is 5V as it goes through the regulators 5V is okay. The TX and RX lines to the BV103. A jumper must be placed across the bottom two pins as shown, with this jumper in place it is possible to get access to the AT commands.

When switched on the IND LED will flash mush slower then normal this means that it is in the correct mode. Use BV_COM2 again but this time the Baud rate is 38400. There is a Bluetooth script that will make life easier for this. The AT command set will also be required which is here.