The blue wire just creates a common ground between the
Amigo and the nine volt battery.
That completes this introduction about extending your
Amigo to the world outside the circuit board. With two
Color BASIC commands and some simple hardware, you
can greatly expand the fun (and learning!) you and your
student can have with your Amigo.
Some things to remember:
A=INA[x] converts the voltage level on pin x to a 1 or
0 logic level in variable A. OUTA[x]=1 places 3. 3 VDC on
pin x; OUTA[x]=0 grounds pin x to 0 VDC.
Always use a current-limiting resistor between the I/O
pin and any circuit using a voltage source other than the
3. 3 VDC from your Amigo.
When using a transistor as a computer-controlled
switch, don’t forget the bias resistor
between the transistor and the I/O
pin. If you don’t have the specs for
your transistor, check the Parallax
forums, or do a quick Internet search
for images associated with “I/O pin
<your transistor here>.”
Consider a separate power
source for motors or other beefy
computer-controlled loads. Don’t
forget the snubber diode if you’re
controlling a motor!
Of the 16 I/O pins brought out
to J8, P0-P4 are used to interface the
Prop chip with the Amigo SRAM and
SD card, but are still available for use
after considering that constraint. Pins
P5-P15 have no assigned duties and
are exclusively available for your use
with the Experimenter’s Section.
I hope these simple computer-controlled hardware circuits will bring
you some smiles, and will fire up your
imagination for cool things you can
do together with a student and the
Amigo. Future Nuts & Volts articles
will discuss how your Amigo can
measure resistance, hack an RC toy
car, and some other fun hardware
projects. Until then, be well! NV
Perhaps the easiest way to build
your own Amigo is from the kit
available from the Nuts & Volts
webstore which provides everything
you need, including the circuit
board, all components (including an
EEPROM pre-loaded with Color
BASIC), and a 2 GB SD card with
sample programs. However, if you
already have a Propeller board with
connectors for a PS/2 keyboard, VGA
monitor, and 2 GB SD card, you can
“roll your own” Amigo by
downloading the Color BASIC
source from the article link, updating
the I/O pin assignments to match
your hardware, and then loading the
compiled Color BASIC binary to the
EEPROM on your board.
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40 September 2016