Over the past few years, I’ve built several little “retro computers” to help young family members and friends learn introductory programming, and it’s been fun and rewarding. I
also wrote a book for parents and/or grandparents to
guide the learning experience, mentoring their youngsters
on the fundamentals (emphasis on “fun”) of programming
and computer-controlled hardware. Most of these
“mentoring platforms” were built from kits based on the
Parallax Propeller, and they used that amazing chip to host
a tinyBASIC interpreter and drive all the I/O for a self-contained “old style” computer: keyboard, monitor, file
storage, audio, and joystick.
My favorite of these kits was the Propeller
Experimenter’s Board (PEB 2014) which is a version of the
“Pocket Mini Computer” from Jeff Ledger at
propellerpowered.com — easy to build, full of features,
and loads of fun. For me, the PEB 2014 and its Color
BASIC “operating system” bring to mind the Commodore,
Atari, and Tandy computers of the early 1980s, which
were easy to understand and program, and were ready to
go as soon as you hit the “on” button. (The PEB 2014 has
just 4K of program memory, and to me is eerily
reminiscent of my first TRS-80 — a 4K Color Computer.)
Those early machines were so much fun precisely
because they were easy to understand and program, with
no hidden layers of complexity or steep learning curves.
They were directly responsible for the career choices of
thousands of today’s sweetly successful hardware and
software engineers.
Hola Amigo!
I believe that this “simple and fun” formula still works.
So, when the PEB 2014 was no longer available from
Propellerpowered earlier this year, I was disappointed
enough to design and build a simplified replacement that
preserved the features most important to me: easy to
build (perhaps with a youngster helping); easy to program
(using Jeff Ledger’s generously licensed Color BASIC);
containing a breadboard with access to some Propeller
I/O pins; and sporting an “old computer” monitor and
keyboard.
I call the result the “Mentor’s Friend,” and nicknamed
it “Amigo.” In this article, I’ll attempt to explain what the
Amigo does, how it works, and how you can build one
(Figure 2).
Figure 2 shows the features and interfaces of the
Amigo. It uses an old PS/2 keyboard and VGA monitor as
primary user interfaces, and comes with onboard
connectors for a Wii classic controller (not the nunchuck)
and earbuds or a powered speaker. The Propeller itself is a
40-pin DIP package (to allow easy DIY construction), with
the standard 5 MHz crystal, reset switch, and Prop Plug
connection. The EEPROM holds Color
BASIC — the Propeller Spin binary
that boots up a tinyBASIC interpreter
and drives the various input/output
channels via Prop I/O pins. The 2 GB
SD card supports non-volatile storage
of BASIC programs and data files, and
the SRAM chip provides 32K of
volatile data storage.
The Experimenter’s Section
contains a small breadboard (the
same one used on several Parallax
boards), two tact switches and four
LEDs, and headers for access to Prop
pins P0-P15, the switches and LEDs,
and power and ground. The power
supply provides 5 VDC and 3. 3 VDC
to all of the above as needed.
(Way) Back
to BASICs
The “secret sauce” of the Amigo
is (as mentioned) Color BASIC: a
Propeller Spin program with roots
back to 2006 and a history of
contributions by a plethora of
Propeller gurus. Color BASIC was
Vintage Computing
FIGURE 2: The Amigo, showing key interfaces and the
Experimenter’s Section.
38 December 2015
