iRobot Create - Arduino interface cable

This post details the construction of a custom Arduino interface shield and cable for the iRobot Create. See my tutorial series on the iRobot Create. This cable allows the user to easily and cleanly interface with the Create and communicate with it via the Arduino Mega2560's Serial1 port.

Parts List:

• DB25 Connector (parallel port connector)
• Protoshield (or THIS)
• Ribbon Cable
• Ribbon Cable Connectors
• Male Headers
• Colored and Black Wire

Assembly is fairly self explanatory when you see the pictures. Here are a few useful charts.

Arduino Mega Pin	Create Cargo Bay Pin
TX1 (pin 18)	RXD (pin 1)
RX1 (pin 19)	TXD (pin 2)
GND	GND (pin 14)

The chart above shows the connections that must be made. Note that Serial0 on the Arduino cannot be used without additional external hardware.

First things first, assemble the protoshield as per THESE instructions.

Next, solder the ribbon cable to the DB25 connector. I chose to do it in such a way that the pins would be mirrored on both end. Note the way the ribbon cable connectors work, every other wire is connected to the top row. Really, the only important thing is that you include pins 1, 2 and a ground. Crimp the ribbon cable connector on.

Now you need to solder on some male headers to the protoshield. This is where the ribbon cable will connect.

Connect the male header that corresponds to the ground to the ground pin on the Arduino. Use the colored wire to make a jumper that will go from the RXD and TXD pins to the Arduino TX1 and RX1 pins respectively (in the picture below, it is the black and white wire in the bottom center).

Note that Serial1(TX1/RX1) must be used on the Arduino Mega (the Uno will not work without external hardware). The serial port output TXD from the Roomba/Create is too weak to drive the RX serial port (Serial0) input of an Arduino properly. This is because of the USB-Serial converter on the Arduino: it also tries to drive the RX serial port input via a pullup resistor, but the Roomba does not have enough drive to pull the RX down below about 2.5 volts, which is insufficient to be reliably detected as a TTL serial input of 0. Furthermore, using Serial1 still allows for the use of the Arduino Serial Monitor for debugging purposes. Also note that Serial2 or Serial3 could be used if selected in software.

Test your board and see if it works!

I hope this post was somewhat useful. It isn't so much of a how to as it is a description of what I did. There are many ways to do it. Really, the only important thing is that you connect TXD to RX1, RXD to TX1, and GND to GND. When you do that, you'll be ready to head back to my tutorial series!

Matthew