a LOGICal replacement for the carbon-track pot

At a certain age, children are often packed off to bed with the final admonition: `All right, you can read in bed for a quarter of an hour, but then you must turn off the light and go to sleep`. However,. as most parents will know, the children tend to suddenly loose all sense of time in this situation ... When a member of the Elektor design team was faced with this problem, he started looking for an electronic solution. The final circuit, as published here, has proved extremely effective. Ever since the onset of this Electronic Age, the zippy electron has been steadily taking over from the cumbersome mechanical and ► electro-mechanical equipment in a wide variety of applications. Signalling and other data transmission systems, calculators and business machines, clocks and watches, for instance, are obvious examples. A firm last stand, however., seems to have been made by the familiar carbon-track potentiometer. Despite its inherent deficiencies such as inaccuracy and short usefu I I ife it has retained its popularity, particularly in the field of entertainment equipment, because it is cheap, easy to use for all kinds of controls in electronic ` l circuits and is often easily replaceable. The trend now is to I im it the use of these devices which have a habit of becoming noisy in their old age, and in advanced circuitry they have been largely replaced by controls such as . varicaps, variable-slope transistors, biased diodes and other electronic devices. This article proposes further relegation in that the control voltages for a circuit are not even derived remotely from carbon-track pots, but from logic which produces the voltages entirely electronically, from finger-tip touch sensors.