Parts arriving and work begins on both Schmitt Trigger Conditioner and the ASR-33 Reader Power Supply

PCBS AND ALL COMPONENTS CAME TODAY FOR THE CONDITIONER

The boards arrived from JLCPCB today, the components that came earlier this week from Digikey. Tomorrow I can solder together a board, giving me five channels of incoming signals from the Virtual 2315 Cartridge Facility (V2315CF) that I can condition so that they deliver reliable edges and no bounce or glitches. 

The signals are generated by an open collector gate in the V2315CF that is driven by the Lattice FPGA. It produces such sharp edges when it pulls the signal low that at the other end, where the signal enters the IBM 1130's Solid Logic Technology (SLT) circuitry, we get undershoot and ringing which can appear to the SLT logic as more than one falling edge. This throws off the logic and produces erroneous results. 

The conditioner employs hysteresis, via a Schmitt Trigger operational amplifier (op-amp) whose thresholds are 4V and 0.7V. This ensures that once a signal drops below 0.7V, the SLT logic sees a logic low and  will not see any change until the input passes above 4V where the SLT input becomes a logic high. All the ringing below the 4V level is completely ignored. The undershoot is ignored as well. 

MOLEX CONNECTOR PARTS ARRIVED AND FIRST CONNECTOR WIRED UP

The shipment from Mouser arrived with the Molex 15 pin connector bodies and male pins needed to create the plug that the Teletype Model 33 ASR connects to for the purpose of powering the paper tape reader and implementing the automatic start and stop of the reader. I assigned wire colors to the 13 connections on the plug that are implemented. Two pins are used on the original Teletype power supply to complete a circuit when the reader is running - that circuit is available for custom purposes and not used in the machines where my replacement power supply will be used. 

EXPECTING PARTS TOMORROW AND PCB ON MONDAY FOR READER SUPPLY

The other components for the power supply are arriving tomorrow from Digikey and the PCB for the supply is expected to be delivered Monday, after it was produced at JLCPCB. Thus on Monday I can solder together four of the PCBs, creating two power supplies for the automatic reader version of the ASR-33 and two supplies for the manual reader version. The manual reader version simply omits some components on the PCB and the associated wires to the Molex connector. 

GLUE UP OF CABINET FOR VIRTUAL 2315 CARTRIDGE FACILITY BEGUN

I began gluing together the acrylic pieces that form the cabinet for the V2315CF. This consists of multiple sheets of acrylic, laser cut to dimension, with rectangular rods used as braces at all the intersections. I leveraged a wood box for its right angles and good support, adding clamps to hold the parts together while the acrylic glue joins the pieces.