Servo - January 2013

problem! Modify the connector!

Using a small-tip pair of long-nose pliers, carefully grab the plastic stud and twist it until it snaps off. The registration slots on the metal case of the connector will properly align with the Roomba mini DIN connector, and everything will work fine. See Figure 7 for a typical mini DIN six-cable connector which clearly shows the center plastic registration stud removed. (In Figure 6, I labeled all of the pins but one — pin 6.

Table 2 gives the description for all of the pins, whether we are using them or not.

Unless you have a mini DIN connector with seven pins, you won’t be able to use pin 6 which will limit the current that you can pull from the battery for this connection. For our use with a low-power microcontroller, this won’t be an issue. If you are going to try to power a PC104 board (high current requirements), you might want to use a separate battery and use pin 7 to make your grounds common.

The iRobot SCI interface protocol is not in ASCII, so you can’t use a terminal emulator to talk to it. Because of this, iRobot thoughtfully did not require you to use an RS- 232 level translator to use the port; you can use the serial output directly from your microcontroller to talk to the Roomba.

Many people call the asynchronous output from a UART on a micro “RS-232.” It isn’t. RS-232 refers to the electrical specification that describes the signal levels that appear on the other side of the RS-232 level translators that you attach to your microcontroller. This causes some confusion, so be the first on your block to correctly name this.

The iRobot SCI specification states that this is a 0-5V logic level, so if you are using a micro whose native output is 3.3V, you will have to do a level translator which isn’t hard. (See my October 2012 article about using a wireless PS2 controller which gives a good circuit for doing this voltage level translation.)

iRobot is pretty coy about their manuals for hacking the Roomba, so you aren’t going to just navigate their site to find them — at least I couldn’t find them by wandering the site. However, you can find them using their search window. Here are a few of the fun things that you can find; some of them are for the iRobot Create, which is their hacker hobbyist-only version of the Roomba. The one that we’re interested in is the iRobot Roomba Serial Command Interface Specification. Here are the manuals that I found on their site:

1

2

3 Rxd

Figure 7

and start controlling the Roomba from an Arduino. Yeah, I’m going to use the Arduino for a couple of reasons: It is easy to use and I’m essentially lazy when it comes to reinventing a wheel. If someone has already written an SCI command translator interface for the Arduino, I’m gonna use it! The Arduino is a 5V microcontroller system, so we can interface its UART directly to the SCI connector and run.

I’ve looked through this manual a little and noticed that you can set the Roomba to a variety of modes. You can not only control its motors, but also get detailing information about the state of its many sensors. It doesn’t look too hard to use, either.

So, until next month, think about the possibilities or jump the gun and write to me with your findings, suggestions, or requests.

I’ve come to the end of another Mr. Roboto column and it seems there is still so much more to do! That is the wonderful thing about a hobby — especially this one. There is always more to do! So, send me your emails to roboto@servomagazine.com and I’ll do my best to answer them. SV