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Ok, am I a little harsh, maybe, but when you have a keyboard that you don't use very much, just think of the wasted CPU cycles scanning the Keyboard! I one minute, in one hour? So what to do? In steps our 8 input to 3-line, Priority Encoder TI SN74x148. A0 A1 A3 = GS H H H 0 H 0 0 1 4 L Table 1   Ok, you ask what is a Priority Encoder? Put it simply it is a device that will generate the proper output for any given key. Without a keypress, the encoder's output is 0.(update #2)  So let's ...
Well, pigs fly! And I straightened both the back panel and the front panel. But alas I have miss laid the finished front trim panel.  So I'm going to resemble it without the outer front panel, and then do it all over again when I find the damn outer panel. So here goes. All of the labels have been lost strayed or stolen.  So this will be done in the blind! And of course, there will be lots of pictures. The ammeter works, but it will need a new scale, about 20 to 40 bucks and a new jew ...
Well, here we are again, the MAX6955 went down in flames as it will only work on LEDs. So we have to start over. The Analysis: The NCD is comprised of 4 groups: Display, Keyboard, Rotary Switches, and Thumb Wheel Switches.  The Display is comprised of 4 16-segment and 13 7-segment PinLite lamps, and two LEDs.  The keyboard is comprised of a 10 key number pad and 4 special keys, it also encodes A-Z. There are two rotary switches, and two thumbwheel switches as well. I also found a user ...
OK, last time I might have confused you with 2-level interrupts. So here it is and please refer to the schematic. So here's how it works. In this diagram, you see 4 switches 2 rotary and 2 thumbwheel switches.  You will notice that each of the two rotary switches are inputs to 8 to 3 priority encoders and 8 input NAND gates aswell. And the Thumbwheel switches do not have them as they already have BCD outputs. So we can just use their raw outputs.  Also, the Thumbwheel switches are also ...
Oh my lord back to this monster again. I took another look at what's really going on in this thing. Display Switch Mode Switch Thumb Switch 1 Thumb Switch 2 int 1 int 2 int 3 int 4 Keyboard int 5 Communications int 0 I have broken it down into functional sections. By using the Arduino Mega I have  6 hardware interrupts 0 - 5, which will take care of the I/O.  Below you can see my logic for the hardware. Basically by grounding the common of the switch which is the inp ...