Page 42 - Hacking Roomba

Chapter 2 — Interfacing Basics 23

It turns out the 8-pin Mini DIN cables used for old Macintosh serial cables are mechanically
and electrically compatible with the 7-pin variety. Because of the wide availability of the 8-pin
Mini DIN cables and jacks, they are much cheaper than 7-pin and they will be used as the
ROI connection components in the projects in this book unless otherwise noted.
Figure 2-2 illustrates what an 8-pin Mini DIN connector looks like.

8 7 6

5 4 3

2 1

FIGURE 2-2: Mini DIN 8-pin socket pin-out

It looks very similar, which is good. All the pins in the 7-pin jack line up with an 8-pin con-
nector. The extra pin in the 8-pin cable goes into the hole meant for the plastic guide pin in a
normal 7-pin connector. Due to the extra pin, all pin numbers after pin 3 are offset by one, which
can lead to confusion when wiring up cables. Table 2-2 demonstrates the signals for each pin.

Table 2-2 Roomba ROI 8-Pin Mini DIN Connector Signal Names
Pin Name Description

1 Vpwr Roomba battery + (unregulated)
2 Vpwr Roomba battery + (unregulated)
3 RXD 0–5V Serial input to Roomba
4 n/c not connected
5 TXD 0–5V Serial output from Roomba
6 DD Device detect (active low), used to wake up Roomba from sleep mode
7 GND Roomba battery - (ground)
8 GND Roomba battery - (ground)