Page 231 - Hacking Roomba

212 Part III — More Complex Interfacing

If you do build your own SitePlayer Telnet Roomba adapter circuit, be sure to thoroughly test
it before plugging it in, and when plugging it in, use an Ethernet hub or switch. If anything
goes wrong, it is better to destroy a $30 hub than the built-in Ethernet port on your computer’s
motherboard.

FIGURE 11-6: Finished SitePlayer Telnet Roomba adapter

LF1S022 RJ-45 Jack
The only odd part of the SitePlayer circuit is the RJ-45 jack. It is designed for 10base-T
Ethernet and is available cheaply from NetMedia. Each row of pins has the standard 0.1˝ spac-
ing that matches breadboard spacing, but the rows are offset from each other by half a row. You
can get around this by inserting the jack into a breadboard at an angle and then carefully rotat-
ing it to bend the pens slightly. Figure 11-7 shows what the pins look like after doing this. This
weakens the jack pins and surely causes other problems, but for prototyping it works fine. If
you’re squeamish about doing this, SparkFun sells an RJ-45 breakout board for 95 cents.

You may be tempted to forgo the RJ-45 jack and wire an Ethernet cable directly to the circuit, as
was done with the serial tether’s DB-9 cable. Do not do this. Ethernet is a much faster protocol
than RS-232 and more care must be taken with cable interconnects and signal filtering. The
LF1S022 jack deals with all of that for you.

Roomba Prototyping Plug
The constructed circuit in Figure 11-6 shows a different method of connecting the Mini-DIN
8-pin Roomba cable. Instead of directly soldering the wires of the cable to the circuit board,
you can install on the circuit board a female header like that used for the SitePlayer or