Mocking up the 1131 controls and outputs

I finished up the LED matrix panels and installed the final connectors. Included the wires to power the six indicator lights that sit to the left and right of the keyboard on the tabletop of the 1130, so it is ready to install in the enclosures. I attached it temporarily to a triangular mailing tube of appropriate size, to use this as the display pedestal until the final enclosure is ready. I also stuck the rotary switch into place with a mock legend and put a picture of an emergency pull disk on the other side. If I can work up a quick transparent overlay upon which I can stick the pattern on the 'smoked glass' I will have a reasonable quick and dirty mockup for continued use.

Quick and dirty stand for LED matrix and rotary switch
The real thing, lights hide behind the 'smoked glass' plate
The paper tape reader has a single module that implements the photodetection of holes in the tape, whose operation must be determined by experiment and reverse engineering because no information seems to exist on the unit, the purpose of the ten wires connected to it, or its interfacing needs. It appears to have one wire per channel plus a common lead, which is colored block thus presumably a common ground.  I found a circuit from a GE paper tape reader that appears to use the identical sensor array, which gives me a starting point for the design.

My variac (autotransformer) and a power connector for the Documation card reader arrived today. I wired up the reader and brought up power slowly, but the fuse blew on the autotransformer. When I opened it, I found that the output terminal had rotated inside and was touching the common (neutral) terminal, thus the short that fried the fuse. Once I get my hands on a 10A fuse, I will try again to validate that the power supply is okay. If it comes up without any excitement, I can put the reader in local mode and test that it reads some cards okay.

I began the strobe interface design and creation of a breadboard version for testing, having found some DIP chips (shift register 74194 and NAND 74ls00 and dual D FF 7474) in my bag-o-chips allowing me to try out some ideas before going to local shop for parts. I have debouncers on another prototype board I will leverage for this test circuit, since I need to debounce the directional buttons on the plotter.

I made an imprecise 120 Hertz oscillator built with a pair of NAND gates and appropriate R and C values. While not stable in frequency or ideal, it works well enough when all I need is a rising edge to occur in the range of 120 times per second. This is used to move the pen or drum at the same speed as the IBM plotter (120 steps per second), when the fast button is pressed, otherwise each press of a direction button causes the relevant shift register to take one step. The buttons are used to select the direction of shift for the associated shift register, plus that signal is passed through a delay before serving as the clock of the shift register. The delay is in place to ensure that the selection lines on the shift register have stabilized before the 'clock edge' is received. The 'fast' button will cycle the clock line up and down as long as the delayed signal is still high, causing the shift register to shift on edge rising edge.

I will be replacing the buttons with a rotary switch, spdt momentary-off-momentary, with a knob similar to the Calcomp or IBM 1627 plotter knobs. This does not change the interface or my logic at all, it is purely cosmetic.

The input board has been tested and is working perfectly on all channels and with both multiplexor chips. I will be wiring some IBM style buttons and the rotary switch through this and activated the input board as the means of operating the 1130, instead of the digilent fpga board buttons and switches that had been used up until now. Similarly I will hook up the LED matrix and led driver to display status of the machine from now on. In a bit more than a week, I will get the keyboard interface card back from the fab and can install components and begin using the keyboard too. When the typewriter parts arrive and I get it fully operational, I will add it along with the console bit switches.

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