Version 2 of LED display driven by the parallel port under tcl control

by Theo Verelst

Using the connection from applying the parallel port to drive a LED and read a switch from tcl, I extended the hardware a bit, nothing fancy, though I'm sure a bit more than most hobbyists will put together just like that, so I've taken time to make a schematic diagram, which makes for a nice little circuit under tcl control.

The image above is the purpose: 3 (I happend to have 3) 7 segment displays (including dot), under control of a tcl program, over a normal parallel port. Cost of the harware, depending on how you built it, I guess 20 $/E, I don't know exactly. The idea is that when you have a running computer it doesn't need to have its screen on to display a number, or, in my case, another, self built computer can use this display unit after it has been tested on a PC.

And its fun.

Assuming the cable from the page I mentioned, and the driver (when needed) from the parallel port page, I used 4 8 bit latch (memories/buffers) chips, in this case from the HC series, though one may want to use ttl (ls) logic, which should work fine, too, to store the data for all the segments of the displays, and to store in this case 3 control bits, to determine which display will be listening to the data bits of the printer port.