Computer and Circuit Technologies

My first personal computer was an Ohio Scientific Challenger 1P. I bought this computer in the late 1970s for $349.



The C1P was a 6502 microprocessor based machine with 4K bytes of ROM that included the operating system and a BASIC language interpreter. As can be seen, the entire computer including the keyboard was built on a single PC board.

The output of the C1P was baseband video, and I remember building a channel 3/4 modulator from a little kit so my computer would display characters on a standard TV set. The C1P had an audio input and output. These were for the purpose of storing software as audio tones on a cassette tape recorder. Having saved the program on tape, you could play the tape back into the computer. The computer would convert the tones into digital ASCII code and accept the ASCII code as though someone was typing on the keyboard.

Being a hardware geek, I immediately took the C1P apart. One of the things I wanted to do with the computer was to interface to other electronics. As I recall, the C1P didn't have so much as a serial port, so I designed and built a bi-directional parallel port interface for the computer. Since, the 6502 processor used memory mapped I/O, the parallel ports could be accessed using the BASIC "peek" and "poke" commands. I even laid out a printed circuit board to replace my wire-wrapped prototype. I then wrote a magazine article on the project which was published in "Kilobaud Microcomputing" magazine in 1981.


The board actually worked quite well. In fact, I used the C1P and the board as the basis for controlling a factory telecommunications tester called Test-set 288. This test set tested a particular type of central office telecom equipment. It had banks of pushbutton switches that had to be manually switched in different arrangements for each of the tests that were to be performed. The technicians that operated the 288 had to memorize dozens of switch sequences to operate the equipment.

Having built and tested my parallel port board, I convinced engineering management at GTE Lenkurt (where I worked as a test supervisor at the time) to let me design an interface between the 288 test set and my Challenger 1P port board. The idea was to use open collector drivers (and in some cases) analog switches to actuate the 288 switches automatically under computer control, and to read meters using the Challenger 1P. Test engineering built an interface unit that I had designed, while I wrote the control software in BASIC to do the testing. That is how I got GTE to finance what eventually became my senior engineering project for UTEP. It also helped to get me a job in the engineering department at GTE Lenkurt. The engineering manager was kind enough to hire me as an engineer while I continued to work toward my EE degree.

I've been designing circuits, developing computer interfaces, and writing software for decades now. The technological advances that have taken place over those decades have been enormous. The memory that filled the large computer room where I worked in 1973 now fits on a keychain. But, I have also grown up with the technology, advancing along with it (another of my patents issued in 2008). Best of all, I still find engineering to be great fun.