Arty computers

On 2/1/07, Fred Cisin <cisin at xenosoft.com> wrote: An analog meter? I hacked one onto a machine a couple of years ago... it was a simple resistor ladder with a 3" panel meter attached to the output. It wasn't precise - the needle would dip when going from 0x1F to 0x20 or from 0x7F to 0x80 since the values were approximage, but it did the trick. One thing I did do was to hack the internal resistor in the meter to match the output levels that a modern desktop parallel port could provide (ISTR the original meter scale was 0VDC - 10VDC and I dropped it to approx 0V - 5V). All one does at that point is to write a tiny app that takes a number from 0-255 and emit it on a parallel port, and the needle swings to that point. You can't change it rapidly due to physical inertia, but for slow changes, it works great. If you want a digital representation of load, you can either drive the LEDs directly from the parallel port, or to get more than 8 lights http://www.switkin.com/software/geeklights/index.html I recall looking at them at one point, but they are essentially a forest of jumpers to light various segments of either a 2 or 2-1/2 digit LED - no drivers whatsoever. One _could_ light them up under computer control, but you'd have to roll your controls. Long ago, I did hang a pair of Radio Shack 7-segment LEDs off of a PET User Port with some trivial logic to use the 8th bit to select digit A vs digit B, then the lower 7 bits of the port went right to the segments. A small machine-language routine tapped into the 60Hz clock interrupt refreshed the digits. For a modern machine, I'd recommend some sort of external latch and multiplexer at least, or perhaps a dedicated LED driver like the ICL7218 (MAX7218?) (here's one I made a while back with 16 digits from one parallel port and two driver chips) http://www.penguincentral.com/retrocomputing/retrogaming/scoreboard.html -ethan