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This simple board was designed to allow the connection of older equipment that uses a DB9 serial port to connect to a computer to USB.

The board holds a Mini RS232 - TTL Converter Module Board that fits in a DB9 connection shell.

connect a USB – TLL module to the board header for USB to RS232.

Components required, DB9 plug and shell, Mini RS232 - TTL Converter Module Board, and a USB to TLL module using the chip of your choice.

The board will need slight adjustment, as it is just a

bit big for most DB9 shells, have found the DB9 shells can be slightly different, please check first.


File a small amount (less that 0.5mm Should be enough) from the end closest to the header holes, opposite end to the DB9, also the shell mounting holes may need a slight file inwards, test on D9 shell as should still be a firm fit. 


When soldering the MAX 3232 module position the module so the SMD components sit in the cutout. Note: some modules available may have a different SMD layout.

As there are no holes in the RX and TX pads on the module, its best to solder from the bottom allowing the solder to wick through the holes to the module pads. Make sure the module is sitting centred on the PCB solder pads.


When soldering the DB9 connection I recommend sitting the board and connection in the shell half to allow correct placement for the connector and board.

Some connectors may be a bit tight slipping over the board, if tight you may be able to file or sand the inside of the pins slightly or bend them out a bit, if tight its worth using a female connector to make sure the pins do not move in the plastic when soldering the connector to the board.


The DTR and CTS pins are only connected from the header to the marked pin holes if required connect a wire from the marked holes to the D9 connector. They where put there to allow extra wires to be connected to the DB9.


 Once the board is ready solder some suitable cable from the header mounting holes to a suitable USB – TLL nodule, the TLL-RS232 board can be used with 3.3 or 5V.


The header pins may not match the USB-TLL nodule pin layout, I have labelled the board to connect RX to RX and TX to TX


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USB to TLL to RS232
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