Apple II & IIe: Power Supply Input Frequency Limitations
Heh. Chris pointed out an amusing old school tech note still live on Apple’s support site.
This one seems to be the lowest # still active.
The Apple II and IIe power supply is a switching power supply. It is designed to accept 107 to 135 volts from DC to 60 Hz.
It will also work at up to 400 Hz but this endangers a circuit which protects the supply from shorting to the point that the protecting circuit will not work.
Of the ones I found, this is my favorite.
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The analog inputs on Port A and Port B of the Apple III are designed to read a voltage between 0 and 2.4 volts and convert it to a number between 0 and 255. The schematic on page 82 of the Apple III Owner’s Guide is drawn for a joystick with 5,000 ohm potentiometers. Only the bottom 20% of the potentiometer’s range is used. Using the +12 volt power supply will result in the most stable readings.
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One of the very first jobs I had was making custom controllers for the Apple ][ and selling them through the local computer club or stores.
As much as I really enjoy modern computing devices and technology, I still miss the days where the manufacturer documented various ports, provided schematics, and didn’t otherwise shy away from wires.
Heck, I miss the days when hooking something up to the computer didn’t require a controller chip. Not that much, really, controllers have gotten dirt cheap and are easy to work with.
May 7th, 2007 at 8:57 am
> I still miss the days where the manufacturer documented various ports, provided schematics, and didn’t otherwise shy away from wires.
I’m glad I didn’t completely miss those days — though the world had already moved on, I grew up with donated Apple ][’s at school and an Apple /// and some yard sale TRS-80’s at home. Unfortunately, by the time my electronics/programming skills had grown enough to actually hack instead of dream, the future was clearly set on $125 standards reprints and wrapping everything three layers deep. I read era literature now (e.g. The Autodesk File) and shudder to think where we’d be if most drivers were still coded at the application level. All the same, if/when I have kids interested in computers I hope to start them on a machine they can get close to.
May 9th, 2007 at 4:25 am
Me too. I remember both the printer manufacturer and the computer manufacturer documenting how things worked, so when the inevitably crap printer driver did something wrong, it was a simple matter to write a better one. I even once built a light-sensitive joystick for the Amiga out of a bunch of discrete light-dependent resistors…had I been any good at programming then I could have invented Dance Dance Revolution a decade early