Re: Apple ii projects for kids?

["Michael J. Mahon" <mjmahon@aol.com>]

mspangler wrote:
> "Only if you need more than 4 bits of output or 3 bits of input. "
>
> If you have a GS, then you have 4 bits of input as the former cassette
> input is now on the game port.
>
> On a IIe if you short the leads on the input filter capacitor, you can
> use the cassette input port as an input too.

It is a "line level" input with an opamp in the signal path, so it's
actually quite different from a TTL input--but it can be used with
proper signal levels and speeds.

> If you are counting pulses, the cassette input seems to work well as
> is. I'm not sure how high or low of a frequency the cassette port can
> handle, but it worked when I used it on a voltage to frequency
> converter. The nice thing about it is that if you mess up all that
> dies is a 741 op-amp.

It is certainly adequate to do frequency counting in the audio
range at line voltage levels (~1v.p.p.)--in fact, that'w what it
was designed to do.  ;-)

> Also on the IIe there is a strobe output ($C040) good for clocking a
> flip-flop or something similar. You could probably figure out how to
> do the same with the cassette output too. That's just TTL with a
> voltage divider. Snip one resistor and you should have TTL voltage
> with adequate protection for the IOU (I think that's where it comes
> from.)

The strobe output is perfect for clocking a shift register, for example.

> And you have the paddle inputs too. A CdS light detector on a paddle
> input is really simple. Low resolution, but if you just want to detect
> day and night, it's easy.

Actually, 8-bit resolution is not bad for many uses.  The trick is
to use a resistor network or an opamp to move the active range of the
sensor to cover a practical part of the paddle resistive range.  An
FET can be used to transform almost any signal into resistance
variations.  The real limitation is the fact that the signal is
averaged over the several milliseconds that it takes to read the
paddle input, so low-bandwidth signals only.  This is certainly not
a problem for temperature and other slowly-changing measurements.

> Any more than that and you are looking at a 6821 or 6522 PIA card.
> Someday when I've brave and not running my tail off on other projects
> (hah, like that will be soon) I'll have to try to build one on an IO
> prototyping card. If someone clones the old Applied Engineering IO 32
> card and it's software I probably would buy it. But really one 6821
> can do a lot.

A 6522 is perhaps the most versatile addition that you can make to
an Apple II if you intend to interface it to a wide variety of digital
devices.  Each 6522 VIA gives you two 8-bit bidirectional ports with
handshaking signals, two timers, a shift register, and interrupt
controls.

A Mockingboard contains two 6522's, each with lots of uncommitted
I/O's, and the timers are free to use when the sound generator is
not in use.

The Jim Bell parallel I/O card, with two 6522's on board, was the
prototypical 6522 card, and it had many imitators--including AE.

If you have access to a card with one or more 6522's on it, get the
6522 datasheet, and you will have all you need to use it for almost
anything digital.

Then again, as discussed previously, if you have a millisecond or so
to read inputs or change outputs, then a chain of latching shift
registers driven by a digital clock output (say, the strobe output)
and connected to a digital output and a digital input can provide
you with practically unlimited digital I/O's with just two of the
Apple's digital outputs and one of its inputs.

As always, the question isn't what *can* be done, but what do you
*want* to do.

If you want to know if a particular interfacing problem can be solved
with an Apple II, describe it and I'll propose some ways to do it
if the Apple can do it fast enough.

If speed is not a burning issue, then much of the solution may be
possible with little or no hardware addition.  The Apple II was
designed as an experimenter's machine, so it's really in its element!

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

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