Sand timers are still common in many areas. They are like time counting symbols and can be recognized of its special shape with sand tanks and thin tunnel allowing sand flow from top to bottom. The only downsize of such timers is that amount of sand is limited and you always have to turn it over after sand leaks out.
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Why to do it yourself – leave this task for Arduino like in this project. It uses an Arduino board that controls whole process, a stepper motor which rotates sand timer when needed and an optical sensor which determines when its time to rotate. But this isn’t it. This so called USB hourglass also uses optical sensors light beam as random number generator. Because falling sand produces some kind of chaos, so the light beam intensity produces some entropy that is sent to PC via USB. This way 10 bit ADC generates random numbers at 100 Hz frequency. Well this is really nice and handy desktop toy.
I can imagine that many years ago some man had to watch sand timer and turn it over periodically in order to know exact time or time interval. Sounds like fun…