What is it?

It's a extension board for the Raspberry Pi which provides two additional RS232 ports. The latest version is almost completely compliant to the Raspberry Pi HAT specification. The only missing thing is the slot for the camera flex cable.

Why did you make it?

I made it because I ran out of serial RS232 interfaces on the Raspberry Pi. You can use it to connect some microcontrollers or Arduino boards. You can also use it as a serial sniffer. A simple program can analyze and forward the serial data to the other port. And you are able to see what's going on on the serial connection between two devices.

What makes it special?

• It adds two extra serial RS232 ports. The available serial port on the extension connector isn't used for this.
• I designed the PCB and used the Dual UART chip SC16IS752 to add the two ports.
• The signals of the two ports are available on 10-pin connectors.
• I also added two short cables with a 9-pin D-SUB male connector.
• The serial port signals have real RS232 voltage levels (not just 3.3V or 5V).
• It works with the Raspberry Pi Model 2 and 3
• Baudrates up to 460800 Baud are working

What's included?

The dual serial extension board is coming without the flat ribbon cables. If you want to have the flat ribbon cables with the two 9-pin SUB-D connectors, please select the option.

How to use it?

The latest version of the Dual Serial Port Extension is working with your Raspberry Pi out of the box! The necessary overlay is provided by the integrated eeprom memory. Just attach the board to your Raspberry Pi and you should get two additional serial devices in Linux (/dev/ttySC0 and /dev/ttySC1).

If you have the very first version without the eeprom, you need to get a copy the overlay from my GitHub repository. Finally, you have to enable the overlay in your config.txt of RPi.

The latest RPi Linux kernel comes already with the necessary SC16IS752 driver.