Pills Reminder

Posted on Feb 7, 2014

A Pills Reminder is a device that operates a flashing LED (and/or a beeper) at a fixed hour interval. A choice of time-intervals as wide as possible is available with this circuit, namely 4, 6, 8, 12, 24 and 48 hours. At first you must choose the hour interval by switching SW1 to the desired value, then apply power by means of SW2. After the hour

Pills Reminder
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delay chosen has elapsed the LED will start flashing at 2Hz, i. e. two times per second. This status will last until pushbutton P1 is pressed: then the LED will turn off, but the circuit will continue its counting and the LED will flash again when the same hour interval as before is reached. A noteworthy feature of this circuit, usually not found in similar devices, is that the internal counter is not reset when P1 is pressed: this allows a better time-interval precision. Let us explain this feature with an example: suppose you have set the time interval to 24 hours and started the Pills Reminder at 8 o`clock. Next day, at 8 o`clock the LED will start flashing, but you, for some reason, notice the flashes at 8:10 and press P1 to stop the LED. With most devices of this kind, the counter will be reset, causing the LED to start flashing next day at 8:10 o`clock. This will not happen with this circuit and the LED will start flashing next day always precisely at 8 o`clock even if you pressed P1 at 9 or 10 o`clock. The clock of the circuit is made of a stable oscillator built around two inverters embedded into IC1 and a Watch crystal oscillating at 32. 768kHz. This frequency is divided by 16384 by the internal flip-flop chain of IC1 and a 2Hz very stable clock frequency is available at pin #3 of this IC. IC2 counter and IC3A 4 input AND gate are wired in order to divide by 3600 the 2Hz clock, therefore, a pulse every 30 minutes...

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