Working on schematic for new PCB for the 1130 extender box; investing time to learn KiCad; sourcing parts

TAKING ON LEARNING CURVE FOR KiCAD

I have used a variety of PCB design tools in the past but have had friends who get great results using the open source KiCAD toolkit. In the past, my designs were small enough that I didn't want to spend the time it would take to learn an entirely new product and all its idiosyncrasies. I had painfully learned over the years how to force the software like Designspark to do what I wanted and how to recover from the peculiarities of each product.

This project is going to take long enough to finish that I can afford the extra delay introduced by switching over to KiCAD, so that is what I have done. At least as far as the schematic side of the product, I am impressed and find it more intuitive and less quirky that past tools. I am hoping that the PCB side is equally favorable, although I will be happy if I at least achieve the same results as I know I could have attained with my old toolbag. 

SCHEMATIC ROUGHLY HALF DONE

The schematic has to deal with 40 driver and 36 receiver circuits that talk to the IBM 1130 CPU over the Storage Access Channel. In addition, there are many circuits for my extensions to SAC, the SPI links and expansion I/O pins I might use to expand the box or attach some real peripherals. 

As an example of the latter, I might build an interface to attach a Documation card reader, making it appear to be an IBM 2501 reader as far as the 1130 system is concerned. I also have paper tape and plotter hardware that I can connect. 

The schematic also includes the power sources and regulation, the LED display drivers and power sequencing connections from the 1130. Since a receive circuit consists of seven resistors and a transistor, the parts count just for the 36 receive channels is 288 components. I will mostly use surface mount parts to keep the space requirements low. 

The secret sauce here is the FPGA board, of course, as the vast majority of the circuitry for this extender box is implemented in VHDL or with the support chips on that Ztex FPGA board. My schematic only has to get the signals to the connector where the FPGA board plugs in. 

SOURCING (AND SUBSTITUTING) PARTS

My receiver circuits used a BSV52 switching transistor but that is now obsolete and difficult to find. I had to switch to an MMB2369 to put on the board. I have been adding parts to a Digikey shopping cart and soon will fire off the order.