Commence landing - wiring up a couple of digits to indicate Program 63

Testing mini-WASP in and wirewrap method while waiting for my plates to arrive

HAND PLACED CONNECTORS AND TEST WIREWRAP

Building connectors with the mini-WASP (MW) connectors consists of pressing all the individual female or male pins into a plate, drilled with holes in an array with spacing .125". I am having wood plates constructed to hold the MW pins in place and support my wire wrapped cabling.

The plates are not going to arrive for a few days, but I did pick up the supply of female MW pins from Marc and therefore could do a feasibility test of sorts right now. The individual MW pins can be inserted onto the male pins of the power supply and other modules. If I wire wrap these to hook up a minimal circuit I can verify that the basis scheme is going to work.

I wired up the Power Supply Module with its 800 Hz input signal, ground, 14 and 28 volt power supplies, the resistor that stands in place of the dimmer potentiometer on the spacecraft, and a pair each of low and high pins delivering the >250VAC 800 Hz that will illuminate the Electroluminescent Panel Module. 

The results were excellent. It was easy to keep the MW pins on the modules and the circuit worked as intended. I believe I will double or triple the wires wrapped onto the ground, +14, +28 and the four AC pins, ensuring that the 30 gage wire is not an impediment to the currents expected when lighting many segments simultaneously. This will be done when the plates have arrived and I construct the final connectors. 

Checking out my 3178 terminal components

INVENTORY AFTER DIGGING OUT ALL MY TERMINAL PARTS

Using IBM nomenclature, the 3178 C terminal consists of a monitor element, a logic element and a keyboard element. The logic element is what I have referred to as a controller box. 

I have two logic elements, thus can have a maximum of two working terminals. I have three monitor elements and three keyboards.

Two of the keyboards are 75 key units, marked C1 underneath, while the remaining keyboard is marked C3 and has 87 keys. 

TESTING LOGIC ELEMENTS

Both logic elements power up and appear to work fine, given that I don't have a coax connected to a control unit and thus see only local functions. It goes into Test mode and paints characters across the entire screen. In Normal mode I have the horizontal green line between lines 24 and 25, with all nulls visible in the remaining locations.

TESTING MONITORS

One monitor is intact and provides adequate but not strong brightness. The second monitor is intact but has a quite dim level, only suitable for a darkened room. The third monitor has a hole punched in the top of the case and when operated has a decently bright horizontal line right across the middle at about line 12 position. 

TESTING KEYBOARDS

All three keyboards seem to operate, as I can type and see some characters show up on the screen when the terminal is in TEST mode. In Normal mode, nothing happens since the terminal does not see the control unit on the other end of the coax. 

The behavior is the same for all three keyboards and across both logic elements. Pressing the alpha character keys yields the capital letter on screen that matches that keycap. However, the special character keys above the alpha top row (QWERTY etc) show up as decimal digits rather than the value on the keycap.

Further, the cursor arrow keys don't move the cursor, they just put certain special characters on screen. Shifting to upper and lower case on the keyboard still generates the same capital alpha letter. 

I don't know if this is the behavior that would occur on a fully functional 3178 while it had no coax connection and was in test mode, or if this signifies some mismatch between the keyboard elements I have and the logic elements. I won't really know until I have the 3174 control unit project cabled up and active with the terminals in Normal mode. 

INVESTIGATING THE BROKEN MONITOR

I opened the monitor element that had a broken top and no apparent vertical deflection. Right away I astutely noticed the electrolytic capacitor laying inside, disconnected from any PCB. The base had oozing electrolyte. 

I examined the PCB inside the monitor and see the spot where this capacitor (C312) had corroded off the board. It is in the Vertical section of the board, quite consistent with the behavior I observed. 

I intend to buy a replacement cap and install it, after cleaning the corrosion off the PCB. If the traces and connectivity check out okay, I will power up and see if the vertical scan resumes operation. At worst case, I have a fully functional PCB on the other monitor, the one that is excessively dim. I also have a good plastic top that I can swap onto this unit. Therefore I expect I can restore this to working order and have two sufficiently bright, working 3178 terminals.

Disappointing news after unboxing - my terminal is a 3178 rather than the color 3179

EXAMINING MY TERMINAL

I finally opened the box I had received years ago, believing it was a color 3179 terminal. Alas, it is the monochrome green 3178 terminal, like my other ones. 

PROJECT GOING FORWARD

This doesn't invalidate my project although esthetically I wanted the full color terminal experience. At some future time I can buy a 3179 and continue that aspect; this should cost in the range of 150 to 200 on ebay including shipping. For now, I will continue with the 3178.

New project - experimenting with my IBM 3179 color terminals

SCOPE OF EFFORT

I own several 3179 terminals and have potential uses for them, but I don't have the control unit that drives and supports them, thus have no way to connect to them. Three possible uses are:

1. I own a P/390 system, which is an IBM PC with a special board that implements the S/390 (and earlier 360 and 370) instruction sets and functionality. It comes with support software running under OS/2 that configures and controls the entire system. With it, I can boot up systems such as MVS or VM that work well with 3179 terminals attached.
   
   Barring the real terminals, I have to open windows on OS/2 to run 3270 emulator sessions, which is just not as satisfying.
   
   
2. Eventually a team of us will recreate an entire 360/50 system. A 3270 terminal is a bit of an anachronism for this mainframe, but I think with a bit of work we can back port support to OS/MFT or DOS operating systems. We will be creating bus & tag channels for the recreated 360/50 and thus if I can create a control unit it could be attached. 
   
   
3. A mainframe emulator called Hercules can run on a PC and also give me an MVS or VM system, but has the same dependence on 3270 emulator windows on the PC rather than using a real glass screen.

Andrew Kay has recently attacked this problem and developed a control unit to drive his 3278 (monochrome) terminal for attachment to Hercules. He has made the code and hardware open source, sharing it with the community.

I am building the interface hardware using his design and PCB layout. This is a shield that mounts atop an Arduino Mega 2560. The shield hosts a coax connector allowing a cable to be connected between the shield and the controller box on a real 3270 type terminal. A USB cable serial stream connects the Arduino to a host system of some type where Python code provided by Alexander will implement the control unit functionality. 

His code makes a TCP/IP connection from his Python code to a TCP socket in Hercules, thus allowing use of his 3278 for software running in an emulated mainframe on Hercules. While this is sufficient for my purpose number 3 above, it may or may not work properly with the color support of the 3179 since he has not tested it with a color terminal. 

To implement my first two purposes from above, I will be modifying the controller. Eventually I would migrate this into an FPGA based hardware device since I will be implementing a bus and tag channel in that hardware to hook to the recreated 360 system. 

I am not yet sure how I will hook into the P/390 system. Some research is required to design the right approach. 

IBM 3179 COLOR TERMINALS

These were a part of the IBM 3270 family of CRT terminals first released with S/360 in the late 1960s and used with mainframes for decades after. The 3179 is a newer version of the 3279 which first brought color to this family; the original 3270 line were monochrome green screens. 

The terminal itself consists of a monitor, keyboard and controller box. Their is relatively little intelligence in the terminal itself, with an external control unit such as 3274 or 3174 providing the majority of the functionality. One control unit would handle multiple terminals typically, as an example 16 3179 terminals might be connected to one control unit. The connection between terminal and control unit is a 93 ohm coaxial cable. 

The control unit itself is connected to the mainframe by one of several methods ranging from local attachment to a bus & tag channel through various telecommunications link types. The programmer communicates with a terminal by sending streams of commands, orders and data to the control unit.

Inside the terminal's controller there is essentially just a large buffer with one location for every character position on the screen. A typical 3179 would have 24 lines of 80 characters plus a 25th bottom line that indicated the status of the terminal. Thus the controller would have a buffer with 2000 locations which was continually drawn on the screen as the terlable for update. Some presses would send a special code instead, for example a Program Function button. 

The terminal controller waits for the control unit to send it a query, for example polling it to see if any key was pressed. The terminal can't signal the control unit or mainframe on its own, it has to wait as a slave device. If a key was pressed, the terminal controller sends codes to identify which key was pressed, as well as status and other information. 

The control unit can ask the controller to send part or all of its buffer, which is used to satisfy the commands and orders coming from the programmer. If the terminal user has typed in data at various locations on the screen and then hit the ENTER key, the response showing the ENTER key is followed by the control unit reading any modified part of the buffer; these are the fields where the user typed in content. 

Writing to the terminal is done by sending updates to the buffer from the control unit to the terminal controller, after which the new data and formatting is visible on the screen. 

Making plates to hold the mini-WASP pins

CONNECTOR ANCHOR PLATES BEING FABBED

I carefully designed the lasercutting outlines for the plates, yielding a total of six plates. Each of the three connector types - Power Supply Module, Relay Module and Electroluminescent Panel Module - have a pair of plates. The lower plate has .07" diameter holes cut through the maple hardboard, into which the nylon holders of the mini-WASP pins will be pressed. The upper plate has .03" diameter holes that are large enough to allow the wirewrap post tails of the pins to stick through but will retain the nylon holders. 

The power supply plate only has 12 pins, but the relay module plate can hold 137 and the EL panel plate an even more numerous 160 possible pins. In my current project I will partially populate the three plates as I don't need every connection. For example, the relay module only uses 81 pins while the power supply is just 7 to 9. 

CONCERN OVER ACCURACY OF FABRICATION

I did the drawing using Inkscape, which is a freeware alternative to Adobe Illustrator. It allowed me to be very precise in the sizes and spacing of all the features. This is essential as the nylon holders must fit in the holes and be spaced in a grid with .125" spacing pin to pin. 

When I uploaded the design file to Ponoko.com, their system showed the size of the group of plates to be almost twice as big as in my drawing. This was quite concerning as accuracy was important. Their FAQs recommend changing the size of the group manually on the website, which I did.

However, my drawing is a collection of six plates with spacing between them, thus I have to hope that they determined the bounding rectangle or size of the group exactly the same way that Inkscape does when I select everything. If this is true, then they should scale properly. However, there is a very real danger that my $55 order will arrive late next week with the plates larger or smaller than designed, rendering them useless. 

Designing test setup using DSKY modules and EL panel

SCOPE OF PROJECT

This project will make use of one Power Supply Module from a block I DSKY, one Relay Module from a block I DSKY and an early version of the EL Panel for a block II DSKY. Controlling all the elements on the display requires four relay modules, thus I can only display contents on part of the EL panel.

I chose to animate the PROG, VERB, and NOUN displays, each are two digits formed by seven segment patterns. I will also light the fixed lines and text legends. Finally, I will animate one of the signs (for the register R1). If I had a second relay module I could light up all of R1 and another sign, for example, but the modules on hand limit me. 

PLAN FOR MINI-WASP CONNECTORS

We have some of the very precious mini-WASP connectors that were fabricated by Samtec to support our Apollo Guidance Computer restoration. I will need roughly 150 female pins for the project as defined. This is a demonstration project and as such I want those pins returned for use in future projects once this one is complete. That requires a strategy for building connectors that leave the pins 'as new' when eventually disassembled.

The normal method to build a mini-WASP (MW) connector is to take a flat aluminum plate and drill .07" diameter holes in a grid with center to center spacing of .125" both vertically and horizontally. The MW pins are pressed into the holes, compressing the nylon body of the pin. The rear of the pins are tall wire-wrap posts, which can be cut down and soldered onto PCBs to form permanent connectors. 

Cutting the pin tails, soldering them, and compressing the nylon by press-fit are all irreversible acts. I had to work out a scheme that did none of those steps yet gave me a workable connector with wiring attached.

The first part of the solution is to use wire-wrap to make the connections. This winds a thin insulated wire around the post that is the pin tail. The post is a square cross section and each of the corners will cut through the insulation of the wrapped wire to make a solid electrical connection. The wire is wound several turns on the post. This does not damage the post at all.

The second part of the solution is to use a softer material for the grid of drilled holes, such that the plate itself is compressed while the nylon remains unaltered. I chose wood for this purpose. I will use a laser-cutting service to build wood plates of .13" thick hardwood with .07" diameter holes cut to hold every pin.

A second plate of hardwood, the same size as the base plate with the mounting holes, will have much smaller diameter holes at .125" spacing, just large enough to pass over the post tails of the MW pins. A dab of wood glue at the outside edges will hold the two plates together forming a sandwich to protect the MW connectors.

These won't be removable with this method, because the cumulative force needed to unset 47 or 91 pins for the two larger connectors will exceed the friction hold of the wood around the nylon bodies. If I try to pull them up, the wood will just slide up off the pins. 

Therefore, these are 'permanently' installed on the modules, with the sandwich pressed down to seat the MW connector to the module side pins, then wirewrapped to provide connectivity. To remove them, I have to first remove all wire-wrap, then pull up the board and finally pull off all the MW pins that remain seated on their companion pins on the modules. This is acceptable for the purposes of this demonstration. 

As with other projects requiring laser-cutting, I will use Ponoko.com as the fab to produce the wood plates I need. The designs are being produced using Inkscape (a freeware Adobe Illustrator alternative).

PLAN FOR CABLING

I will use some form of cable wrap to cover and protect the many discrete thin wires that come off each of the connectors. This is sufficiently robust for the demonstration but hardly rugged enough for a permanent installation. 

There are a few outside wires that will connect to traditional connectors on the connector plates.  These include external power, ground, a source of 800 Hz and all the control signals from an Arduino that will set/unset the relays to activate the module. 

PLAN TO CONTROL RELAY MODULE

The relays are activated by spacecraft level switching, +28V, but the final circuit that drives all of these consist of an open collector transistor that will pull a line to ground to activate or let it float. Thus, my Arduino will need 20 such transistor circuits to fully control the project.

Some simple firmware in the Arduino will provide a command interface over serial to my laptop where I can set the codes for all the digits and the sign. A simple script can run to animate various displays on the panel.