programmable darkroom timer - convenient IC allows simple construction

programmable darkroom timer elektor april 1983 programmable darkroom timer convenient IC allows simple construction Many amateur photographers will be interested in this circuit: a programmable timer for seven preselectable times. The time can be adjusted in two ranges (up to 99.9 s and up to 999 s). Fourteen keys are used for programming. When the start key is pressed, the time countdown can be observed on the display. The preset value then reappears on the display. There is therefore no need for repeated entering of the proper exposure time. 4-56 The advantages of a programmable darkroom timer are well known. Most manufacturers now try to make their equipment as simple to use as possible. An LED display and programming via a keyboard have almost become standard features. Clearly, however, these features are not inexpensive. Elektor has therefore taken the opportunity here to present this circuit of a darkroom timer using a special IC as a low-cost alternative to commercially ava...