Search

MITS Inc., the producer of the Altair, had four founders headed by H.E. Roberts. The company's first products revolved around model rocketry. MITS relied on Popular Electronics magazine for much of its product promotion. The company introduced the Altair personal computer in January of 1975. List price for the computer kit was $397. The Altair was the first personal computer and a milestone in the industry. A photograph of the Altair is included.

In the early 1960s it was very difficult for hobbyists to build computers . The Amateur Computer Society (ACS) was started in 1966 with 110 members. Early hobbyists spent an average of $2100 on the construction of their computers. The first advertisement for a microcomputer based on a microprocessor appeared in March 1974 for the Scelbi-8H. Scelbi Computer Consulting later became a computer literature publisher. A photograph of Nat Wadsworth and the Scelbi-8H is included.

The first home computer kit, the Mark 8, came out in 1974. In 1975 personal computers were called hobby computers. The Altair and other computers preceded Apple into the personal computer market. The original Altair cost under $400 and came with 256 bytes of RAM. A photograph of the author is included.

In the early days of microcomputers it was very hard and expensive to build a computer from a kit. Most early microcomputer companies were small and made little money. Early computer shows were verly different and very little software was available. A photograph of the First West Coast Computer Faire is included.

A small circuit can be added to the Timex-Sinclair microcomputer to eliminate noise and drop out from the cassette tape memory system. Part of the difficulty results from the fact that various brands of tape cassette players are used. Construction and use of a device called the 'Z-Dubber' is covered. Circuit diagrams and parts list are given plus a source for the device in kit form. Oscilloscope images are shown to illustrate the signal pulses.

The TRS-80 Model II microcomputer can become a computerized dialing machine with the addition of a little hardware and software. The system can dial any number from its computerized phonebook. A circuit diagram and parts list are provided for the hardware. Program listings show the two BASIC and one machine language programs necessary to run the system. One program is a report generator for monthly calling records. Use of the system is explained as well as modifications for different dialing speeds.

The direct memory access (DMA) controller chip of the 16-Bit microcomputer is explained in detail. This chip allows peripherals to communicate directly with memory without going through the microprocessor buses. This chip (8237A-5) has four separate channels with a priority ranking. One task done by the DMA is to refresh the computer system's RAM memory. Several clear diagrams make the text readable. A schematic of the computer's power supply system is included.

The video display of the Timex-Sinclair microcomputer can be improved by having a direct cable input to the monitor rather than the radio frequency (rf) generator. It can also be improved by the same device by having a reverse switch built in to reverse the image at will to white letters on black, or black on white. Complete plans are given for this simple two-by-three-inch circuit board to be mounted inside the computer with the reversing switch protruding on the side of the case. The circuit is available also as a kit. By adjusting the values of two resistors, one can also change the size of the pixels making up the characters to improve the appearance of the characters.

This is a project to build a low-cost device which converts microcomputer digital signals into the analog signals of the outside world. The device can become part of an audio-signal processing system, an A-D (Analog to Digital) convertor, or a waveform generator. The heart of the device is the DAC1000 integrated circuit chip. Diagrams, parts list, and brief software for controlling the circuit are included. There is also a special section on the 'Basics of D-A Conversion,' plus a section on the DAC1000 convertor chip. Applications of the device include simple testing of digital and linear devices, amplification of music and other sounds, and regulation of motor speed, temperature, or pressure.

Zenith Data Corporation has produced a new family of dual-processor microcomputers. The 8-bit and 16-bit machines are available also as kits, and the display screen can be a monochrome version or can be upgraded to color. The 128K main memory is expandable to 768K RAM, and there are dual 320K five inch floppy disk drives. The monochrome graphics feature gives TV quality picture resolution. Photographs show the external front, rear, and internal views of the model 120. A table gives technical specifications.

This article is for someone with a certain amount of computer electronics background who wishes to learn about 16-bit technology. By studying a microcomputer building project based on the Intel 8088 chip (the same chip used in the popular IBM-PC personal computer) one can learn such technology and have skills which are relevant to the trends in microcomputer hardware. The basic hardware system covered here is available in a kit for $400, and includes a 64K motherboard and RS232 serial interconnect. One can add on peripherals to build a complete sophisticated state-of- the-art system. Detailed circuitry is drawn out and discussed, but the article is definitely not for the beginner in computer hardware. Future parts discuss the circuits in more detail.