Re: What is the quintessential Apple II?

["mdj" <mdj.mdj@gmail.com>]

Dave Althoff, Jr. wrote:
> Michael J. Mahon <mjmahon@aol.com> wrote:
> : Roger Johnstone wrote:
> : >
> : > We made a new board with a single 8-pin micro on it which performed both
> : > functions. The resistor for the variable time is read by the micro
> : > charging up a capacitor, then timing how long it takes to discharge it
> : > through the resistor. I'm surprised no-one thought of doing that before ;
> : > o)
> :
> : Yes, that's a favorite trick for cheap analog input.
>
> I hope you understand the significance of...I guess it was Roger's
> comment, including the "I'm surprised no-one thought of doing that before
> ;o)", and *exactly* why he said it...
>
> I've been away from here for a while, so I don't know what the 'apple ][
> geek quotient' of the current population is.  But that is exactly how the
> Apple ][ paddle inputs work, discharging an onboard cap through a 150-ohm
> pot in the paddle...

While it's slightly more complex, I've always been fond of using an
bidirectional counter rigged to a DAC (which is usually just an R2R
ladder). The DAC's output and the analog signal is fed to a comparator,
which controls the direction of the counter.

The advantage of this approach is deterministic timing from a very
simple ADC, and the tracking jitter can be easily removed in software
(or hardware if you're that keen).

> Oh, and there are some really neat examples of using not just
> microcontrollers, but full-blown PLCs to flash lights.  In fact...at
> Mariner's Landing Pier in Wildwood, NJ, there is a Ferris wheel that has
> dedicated controllers on it to control 4,600 channels of LED lights.
> There's a video on-line showing a whole cycle of the light show, but I
> couldn't find it when I looked for it...

This problem space is perfectly suited to microcontrollers, since any
sort of interesting pattern can't be easily done in hardware - at least
without employing PROMS, and once you've crossed the line to
programmable components you may as well opt for the uC

Matt