Especially helpful for developing real-time application programs, the circuit in Fig 1 plugs into a PC printer port and measures the execution time of a piece of software. The CD4536 is a 16/24-bit binary counter with a built-in oscillator. This counter has an 8-bit prescaler, which the chip bypasses if the 8_BY pin is high. When this is the case, the CD4536 is a 16-bit counter, and its A through D inputs select which bit is connected to output DO. If the 8_BY pin is low, the CD4536 is a 24-bit counter and the inputs select which 9 to 24 bits connect to output DO. Setting the R pin high clears the counter, and setting CINH high inhibits the counter. With the components values shown in the figure, the oscillation frequency is around 100 kHz. The printer port can directly power the CD4536 because it needs only several milliamps…. [...]

Designers of pen-based computers can easily relegate some controls that were previously mechanical, such as switches and potentiometers, to on-screen icons. For example, the circuit in figure above shows one way that digital logic can control the -24V-dc LCD bias using two general-purpose I/O command lines. The DS1669 from Dallas Semiconductor is a 64-step potentiometer available in 10-, 50-, and 100-kV ranges. The up-count (UC) and down-count (DC) pins digitally control the wiper of the potentiometer. [...]

In this article Bernard Klinc shows us his homemade PCB process.He gives step by step instructions with plenty of pictures. [...]

This page is a guide to producing consistently high quality PCBs quickly and efficiently, particularly for professional prototyping of production boards. Unlike most other PCB homebrew guides, emphasis is placed on quality, speed and repeatability rather than minimum materials cost, although the time saved by getting good PCBs every time usually saves money in the long run - even for the hobbyist, the cost of ruined PCB laminates can soon mount up.This information has been condensed from over 20 years’ experience of making PCBs, mostly as prototypes of boards to be put into production. If you follow the methods outlined here exactly, you WILL get excellent quality PCBs every time. By all means experiment, but remember that cutting corners can easily reduce quality & waste time. [...]

A two-chip circuit which connects to the parallel printer port of an IBM PC or compatible computer provides 16 TTL-compatible i/o lines which are programmable in 4 groups of 4 bits. A short program in Turbo Pascal is given as an example of how to program the interface. The circuit can be expanded at the cost of one additional chip per 16 i/o bits. [...]