Hardware Reference
In-Depth Information
You can remove it using nail clippers, a soldering iron, a saw, or any combination of the above. Just be sure to not
to damage any other components.
Serial Port
You can use a standard serial port for two-way communication between many pieces of old technology such as
joysticks, along with LCD text displays and other forms of home-brew electronics. It also provides a way of controlling
the Slug through
getty
when other routes, such as the network, are failing.
There is already a serial port hidden away at J2 on the Slug motherboard. Alas, its control voltages are 0/+3.3v,
and not the +/−12V necessary for the standard RS-232 serial port, which means you'll require a power-level converter.
(However, strictly speaking, the standard requires hardware to differentiate between voltages in the range of +/−
3-15V.) Some converters can be purchased as a single chip (such as the MAX3232) or already included in some mobile
phone data cables. You can find full details on the web site (
www.nslu2-linux.org/wiki/HowTo/AddASerialPort
).
There are also circuits available that allow you to connect an LCD character display (such as the HD44780) to the
Slug with a minimum of effort, providing a basic (and very low-power) display to report the current media playing or
the machine status. However, this also requires opening your Slug to make hardware adjustments.
LEGO Mindstorms
First released in 1998, LEGO Mindstorms was originally known as the Mindstorms Robotics Invention System (RIS)
Kit and contained a control brick known as RCX to which you uploaded a program with infrared. The software would
then run, control the various motors and sensors connected to the RCX brick, and communicate with others via IR.
This naturally had the usual problems associated with IR as covered in Chapter 1 (primarily line of sight). There were
two versions of RCX released, and both operated the IR at different carrier frequencies (although both RCX modules
can transmit on either frequency) but were functionality identical.
The programming could be done in many languages, including cut-down versions of Java, C/C++, Lisp, and
Forth, provided it was compiled into suitable code for the internal microcontroller, a Renesas H8/300. Because of its
age, it is now available fairly cheaply, although the supplied IR transmitter has no support for any 64-bit operating
systems and is losing support for newer 32-bit ones.
From RCX, LEGO moved to Mindstorms NXT in 2006. This increased the specification of the main brick by
improving the processor (now a 32-bit ARM7/TDMI chip) and communications devices (it now included USB,
Bluetooth, and an onboard 100 × 64 pixel LCD matrix). This upgrade in processor has necessitated a change in control
software, but that is to be expected, and most of the RIS code has now been ported to NXT. The LEGO components
also improved, as shown in Table
2-1
.
Table 2-1.
LEGO Mindstorms Specifications
Kit
Motors
TouchSensors
LightSensors UltrasonicSensors
SoundSensors
ColorSensor
RIS
2
--
2
1
--
--
NXT
3*
1
1
1
1
--
NXT 2.0
3*
2
1
1
--
1
NXT
Education
3*
2
1
1
1
--
* These are servo motors, which internally monitor their position for greater positional accuracy.
Since 2009, Mindstorms has been on its third iteration (NXT 2.0) and consists of the same RCX brick as NXT
version 1.0, some alternative LEGO Technic bricks, and a change in sensor from sound to color. This was an odd
change, as now all NXT 2.0 robots are deaf by default! This might have been a ploy to sell more add-on sensors,
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