pills reminder schematics

The clock circuit is constructed using a stable oscillator that consists of two inverters integrated into IC1 and a watch crystal that oscillates at 32.768 kHz. This frequency is divided by 16384 through the internal flip-flop chain of IC1, resulting in a stable clock frequency of 2 Hz available at pin #3 of the IC. IC2, a counter, and IC3A, a 4-input AND gate, are configured to further divide the 2 Hz clock, producing a pulse every 30 minutes at the clock input of IC5. The division factor is controlled by IC3B, alongside the switch positions of SW1A and SW1B, allowing for the selection of six fixed time intervals: 4, 6, 8, 12, 24, and 48 hours. A set-reset flip-flop, formed by IC6B and IC6C, is activated through IC4C with each low-to-high transition at the selected pin of IC5, as determined by SW1B. Additionally, IC6A and C4 facilitate the setting of the flip-flop upon a high-to-low transition at the SW1B cursor. When the flip-flop is set, IC6D is enabled, allowing the 2 Hz frequency from pin #3 of IC1 to drive pin #13 of IC6D, resulting in a flashing LED operation. The flip-flop can be reset using P1, and a master reset occurs automatically upon power-up through C6 and R7. For those who prefer not to use a watch crystal, an alternative clock generator circuit is available, which directly oscillates at 2 Hz, eliminating the need for divider ICs. A CMOS 7555 Timer IC generates a stable 2 Hz square wave, with its frequency adjusted using two trimmers. R10 is for coarse tuning, while R11 is for fine tuning. Achieving precise 2 Hz frequency settings requires patience and the use of a clock, chronometer, or digital frequency meter capable of measuring low frequencies. Once accurately tuned, this oscillator demonstrates stable performance, unaffected by battery voltage variations, and maintains an accuracy of about ±30 seconds per 24 hours. For optimal time precision, a 5-50 pF 50V ceramic trimmer capacitor can replace C2, and it must be adjusted to read exactly 32.768 kHz at pin #9 of IC1 when using a frequency meter. A piezo sounder, which includes a 3 kHz oscillator, can be added for visual and audible alerts, connected across pin #11 of IC6D and ground, ensuring correct polarity. If the visual alert is not required, D1 and R6 should be removed.

The clock circuit design utilizes a combination of digital components to achieve accurate timekeeping and alert functionality. The oscillator's stability is critical, as it directly influences the precision of the clock output. The watch crystal's frequency of 32.768 kHz, a standard frequency for timekeeping applications, is divided down to a usable 2 Hz signal, which is integral for generating time intervals. The configuration of the internal flip-flops and counters allows for customizable timing intervals, enabling the user to select from a range of options.

The use of a CMOS 7555 Timer IC as an alternative oscillator provides flexibility for users who may face availability or cost issues with watch crystals. This design choice allows for a simpler setup while still maintaining reasonable accuracy, suitable for less demanding applications. The tuning process for the 2 Hz oscillator requires careful adjustment, emphasizing the importance of precision in timekeeping devices.

Incorporating visual and audible alerts enhances the circuit's functionality, making it suitable for various applications, including alarms and reminders. The piezo sounder adds an extra layer of notification, ensuring that users are alerted effectively. The design's adaptability, whether using a watch crystal or a timer IC, demonstrates a thoughtful approach to electronic circuit design, balancing performance with user requirements.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 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, a chronometer or, best, a digital frequency meter capable of measuring very low frequencies.

In any case, after an accurate setup, this oscillator showed a very stable performance, not affected by battery voltage variations and an accuracy of about ±30 seconds per 24 hours interval. Wanting the utmost time precision and if a digital frequency meter is available, a 5-50pF 50V Ceramic Trimmer Capacitor can be used in place of C2.

It must be adjusted in order to read exactly 32. 768kHz on the meter display with the input probe connected to pin #9 of IC1. A Piezo sounder (incorporating a 3KHz oscillator) can be added to provide a visual plus audible alert. It must be wired across pin #11 of IC6D and negative ground, respecting polarities. Remove D1 and R6 if the visual alert is not needed. 🔗 External reference