Finished work on System Source Museum 1053 console printer

TEDIUM PAYS OFF EVENTUALLY - THE TYPEWRITER WORKS WELL

After I exited the loop of adjustments when all character positions were selecting properly in both upper and lower case hemispheres of the type element, I had just one final area to tune up. The 1053 has microswitches at key points in the mechanism to provide feedback to the controller logic inside the IBM 1130 system. These have to be set to fairly exacting points of the mechanical movement, otherwise the controller might start another character print or movement when the typewriter is not in a good position to accommodate it. 

One set are meant to protect the typewriter during 'long' operations. These are movements that take a variable amount of time to complete and are much longer than a single print or shift cycle. For instance, the time for a Tab movement to finish depends on which column we start from and how far away is the next column with a tab set. Similarly, carrier return time depends on how far to the right we were when it is started. 

The other inform the controller when the rotation of the mechanism is at a sensitive point where further commands shouldn't be attempted and then when the mechanism reaches a point where it could again accept requests. Typing a single character involves starting the print cycle from a standing start, moving the type ball and then coming to a stop. 

It is possible to stream an additional character before the print cycle stops, so that the clutch never stops it. The mechanism just continues around in another cycle. This allows the typewriter to reach its maximum speed of just over 15 characters per second, as it is considerably slower if it has to start and stop for each printed character. 

Shifting between upper and lower hemispheres consumes one print cycle, so the actual max printing speed also depends on the specific characters being typed - at worst case it will only print a bit less than 8 characters a second (if a shift is needed between each character). 

I was finally satisfied with its behavior and performance. I put the covers back on and wrapped it up, ready to be brought back to Maryland and enjoyed by museum visitors. 

PRINTER ADJUSTMENTS ARE FINALIZED, READY TO SEND THE UNIT BACK

I was happy to call them and let them know the console printer is ready for pickup. They can get their 1130 back in operation soon. The pickup is this Friday. 

ALSO LOANING A 1053 SIMULATOR FOR TIMES WHEN THE PRINTER FAILS

I designed and built a simulator that plugs into the IBM 1130 and replaces the connections to the 1053 console printer. It delivers the output of the printer over a USB serial link to a terminal or computer where the same results will be seen as would be printed on paper by the printer. 

It provides the same ability to set tab positions, left and right margins, offers a display of the current print column along the line, offers the same return, tab and space buttons for manual interaction, and displays the full character set in both red and black ink. 

It had been initially built with relay boards driven by an Arduino Mega 2560 to provide the feedback signals to the 1130, but the performance of the relays was not sufficient to meet the signal timing produced by the I/O Selectric printer mechanism. With each print cycle taking about 65 milliseconds, the -TWR CB RESPONSE signal would need to drop from 48V to 0 at 7.22 ms into the cycle and return back to 48V by the 43 ms point. 

The relay boards I initially used require up to 15ms to turn on and up to 10ms to turn off. That would have delayed the signal above until 22 ms into the print cycle, way past the safe point where further commands could be issued. Further, it would remain off until 53 ms. Generally these are acceptable for switching rates up to 10 per second, but the 1053 can exceed 15 cycles per second. 

Due to the high speed requirements, I whipped up a small board with four MOSFET switches to instead drive the feedback signals - due to their 12V and 48V levels the Arduino can't directly drive them. A quick check on the breadboard verified the suitability, with the IRF520N transistors I had in the shop turning on and off in mere nanoseconds, approximately a million times faster than the relays could operate. 

The 1053 has two SMS paddle cards that plug into the signal SMS connector block of the 1130 and one SMS power paddle card that plugs into the power SMS block. These are swapped with the cards from my simulator to make use of the simulator instead of the physical typewriter. 

I am loaning the 1053 simulator for an indefinite period to allow the System Source Museum to demonstrate their IBM 1130 even when the console printer, the most trouble-prone part of the system, is inoperative. This also saves on paper use since the paper forms needed for the 1053 have to be custom manufactured and thus are expensive.