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I have been down this road before but now I have the final solution. I found it in my old Motorola M6800 Applications Handbook, section 5-1.1.2 NonEncoded Keyboards. It used a PIA or Peripheral Interface Adapter, since I am using an Arduino I don't need the PIA.  But I will replace it with an I2C 16-bit I/O expander, MCP23017. As you can see I drive the data lines Data-0, 4 with a high. When there is no key closure nothing happens but if a key is pressed 1) the active line is seen on its co ...
I have been working on my C-3436A radio for quite a while after it worked I took it apart to install it in its new home and I could never get the damn thing to work again.  So with way too much time on my hands, I decided to ring out the damn cable once and for all.  Now I can report the job is done. KiCad helped me see my mistakes. This cable is really two cables each terminated with DB-25Ms at one end and ARC connectors at the other. One cable was just DB-25M to a 19 pin ARC connecto ...
Well, a lot of folks have written about the SN74HC595x as an 8-bit shift register. The major use is to expand ports in the Arduino. (image 1) This is the classic way to expand your Arduino for 8 more ports, without resorting  I2C or CANbus.  But what if you need 16-bits as I do? But as you can on the left see by connecting the QH' output of the first shift-register to SER input of the second shift register you can end up with a 16-bit shift register. By adding other shift-registers yo ...