Thursday, May 24, 2018

Nearly finished with conversion of Documation 1000 card reader, now debugging


A sharp eyed reader spotted an error in one diagram of my last post, which used colored green lines to show the wiring of the modification. I mixed up the two chips, 7404 and 7417, thus the wires ran the wrong way. I updated the diagram, quickly and a bit messily; the correct one has two green and one yellow line representing the wires.

My replacement power receptacle arrived and is installed into the reader. I am still rewiring the machine to connect to my interface board, but could turn on power anyway. Everything worked fine this time, with the machine reading the cards I supplied. I wasn't able to see if it properly read the data but the logic was happy, not detecting any checks during the operation.

I cut up a breadboard PCB and installed a dual row female header, to serve as a good soldering anchor for the 17 signal wires and ground that come from the Documation reader. This will plug into the 2x10 header on my interface board. The next morning, I soldered in the wires to the PCB and work on the rest of the installation.

After all wiring was attached, I checked the connectivity to the proper sockets that originated the signal, to be sure I wired the proper signals to each pin of my connector for the interface board. That took a bit of time to work through but everything was correctly routed.

The interface logic will also need connections to +5V, a SPST pushbutton, and an LED. The button and LED are used to indicate end of file when reading in card decks. I drilled and mounted the pushbutton on the front panel of the Documation, with a plan to drill and install an LED holder above it once my holder hardware arrives.

The wiring was installed from power, ground, the pushbutton and placed near where the LED will go in a few days. Those wires are screwed into the interface board on a terminal strip. The last step in the installation is to arrange a secure mounting for the interface board, above the control PCB inside the card cage.

I chose to use some cardboard spaces above and below my board, thus insulating the two adjacent PCBs from my wires or circuit board. The board is held nicely in place between the cardboard spacers above and below.

Board installed in card cage

The code needed to be loaded into the SX28AC controller chip, using my programmer device. I downloaded the Parallax SK-Key editor and tool, which let me assemble the code from Brian Knittel and then load it into the chip on my interface board. I completed both boards, which are now ready to install and use.

I bought a short adapter cord that will hook to the mini-USB on my interface board and presents a full size USB socket for the connection to an external PC. This completes the conversion of the Documation reader. It connects via USB to the CardRead program on a PC, which will control the reader and capture card images onto PC files. The EOF pushbutton and confirmation LED allow the operator of the card reader to confirm the state of the interface.

EOF button mounted, LED awaiting lamp holder assembly
With everything installed, other than the LED holder, it was time to fire up the reader and test out the functionality. The Surface Pro does see the USB board and assigns it a COM port. Unfortunately, the software on the PC complains that it can't communicate with my interface board, so something is wrong. Further, the EOF button doesn't toggle the LED on and off. I will debug it with the second board, outside of a reader. 

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