pills reminder schematics


Posted on Feb 7, 2014

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 orde


pills reminder schematics
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r to divide by 3600 the 2Hz clock, therefore, a pulse every 30 minutes is available at the clock input of IC5. The division factor of this IC is controlled by IC3B and the position of SW1A and B, selecting from six time-intervals fixed to 4, 6, 8, 12, 24 and 48 hours. The set-reset flip-flop formed by IC6B and IC6C is set through IC4C each time a low to high transition is present at the pin of IC5 selected by SW1B cursor. IC6A and C4 provide to set the flip-flop also when a high to low transition is present at SW1B cursor. When the flip-flop is set, IC6D is enabled and the 2Hz frequency available at pin #3 of IC1 is applied to pin #13 of IC6D causing the flashing LED operation. The flip-flop can then be reset by means of P1. A master reset is automatically done at switch on by means of C6 and R7. Sometimes, the Watch crystal can be difficult to locate, or could be considered too expensive. For those willing to avoid the use of a Watch crystal and to accept less time accuracy, an alternative clock generator circuit is provided, directly oscillating at 2Hz, thus avoiding the use of divider ICs. A CMos 7555 Timer IC generates a stable 2Hz square wave, whose frequency must be accurately set by means of two trimmers. R10 must be adjusted first for coarse tuning, then R11 for fine tuning. Setting precisely the 2Hz frequency of this oscillator is a rather difficult task, and can be done with great patience and the aid of a clock,...




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