Microcontroller regulated quartz clock

A generic clock with a mechanically driven display, a standard quartz movement and a microcontroller which is programmed to turn mechanically driven features such as clock hands and counters &#8220;on&#8221; and &#8220;off&#8221; during prescribed intervals of time. A large number of novel derivative clocks can be produced by merely re-programming the microcontroller and making simple revisions to the mechanically driven display. During each tick of the clock, a set of instructions to the microcontoller pulses a stepper motor of the clock in short intervals to further extend the life of the clock's battery.

FIELD OF THE INVENTION

This invention relates to clocks and more particularly to a generic clock with a mechanically driven display, a standard quartz movement and a microcontroller which is programmed to turn mechanically driven features such as clock hands and counters on and off during prescribed intervals of time.

BACKGROUND OF THE INVENTION

The standard quartz clock with mechanically driven hands has evolved into a low cost, highly accurate time piece. In this type of clock, a quartz crystal oscillator produces a sequence of pulses which drive the hands via a stepper motor and gear train so efficiently that the clock's accuracy is held to within one minute per month for more than a year. In some clocks of this type counters and other features are driven in the same manner. High production rates and efficient manufacturing practices have reduced the manufacturing cost of the movement of the standard quartz clock to slightly more than the cost of an alkaline AA battery power supply. The outstanding performance and low cost of the quartz movement have discouraged others from making changes to the quartz movement.

SUMMARY OF THE INVENTION

The present invention overcomes the resistance to changes to the mechanical quartz movement by incorporating a feature in the standard quartz movement which provides benefits and features heretofore unavailable. The feature is a low cost programmable microcontroller. The effect of the programmable microcontroller is so remarkable that the efficiency of the standard quartz movement can be substantially increased. Moreover, a common quartz movement can be used for a large variety of novel clocks.

The invention resides in the ability of the low cost programmable microcontroller to act in combination with the standard quartz movement to cause a clock's mechanical features such as hands and counters to sleep (stop) and awake (start) during prescribed intervals of time.

The low cost programmable microcontroller (computer chip), responds to the clock's crystal oscillator by turning on and off the stepper motor which drives the clock's hands, counters and other features via a gear train. The ability of the microcontroller to turn the stepper motor on and off according to a programmed set of commands provides a number of important benefits.

One benefit is that battery life is substantially increased because current draw is interrupted when the stepper motor is turned off . Another benefit is that the size of the standard quartz movement can be reduced by replacing its alkaline or NiCad AA battery with a small low cost lithium battery.

Still yet another benefit is that a lithium battery can be used so efficiently that the battery's service life is about equal to the life of the clock. Still yet another benefit is that a variety of novel clocks are derived with a common standard quartz clock movement by merely changing displays and re-programming the microcontroller. For example, the microcontroller can be re-programmed to drive an hour or minute hand shaft of an existing clock with the standard -quartz movement to produce a 12-hour clock, a 7-day clock, an ocean tide clock, etc.

A further benefit is that a programmable microcontoller is lower in cost than unique gear trains because of investment savings, inventory savings and higher production rates. Still yet another benefit is that ancillary features, such as alarms, beeps, snooze buttons and dial lamps can be easily incorporated by simple modifications to microcontroller software.

In employing the teaching of the present invention, a plurality of alternate constructions can be adopted to achieve the desired results and capabilities. In this disclosure, some alternate constructions are discussed. However, these embodiments are intended as examples, and should not be considered as limiting.

Further objects, benefits and features of the invention will become apparent from the ensuing detailed description and drawings which illustrate and describe the invention. The best mode which is contemplated in practicing the invention together with the manner of using the invention are disclosed and the property in which exclusive rights are claimed is set forth in each of a series of numbered claims at the conclusion of the detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like numerals designate similar and corresponding parts throughout the several views, a block diagram of an existing Quartex Q84 movement (Lake Geneva, Wis., USA) is shown in FIG. 1 which illustrates a standard quartz mechanical movement. The standard quartz mechanical movement comprises a quartz crystal oscillator 20 , a countdown divider 21 , a stepper motor 22 , a gear train 23 and hands 24 of a clock. As shown in the block diagram, a 32768 Hz train of pulses, generated by the quartz crystal oscillator 20 , is reduced to a 1 Hz. frequency in the 32768:1 countdown divider 21 . The 1 Hz. divider output triggers the stepper motor 22 which drives the gear train 23 . The gear train 23 rotates the hour, minute and second hands 24 of the clock.

The quartz crystal in the oscillator 20 of the standard movement is a high volume, mass-produced, crystal which varies in frequency from part-to-part to about less than 20 parts-per-million. The drift of the standard movement's frequency is frequently quoted as less than one minute per month (23 parts per million). Low cost plastic gears without jewels of the gear train 23 drive the stepper motor 22 and do not require a manufacturing adjustment. The manufacturing cost of the standard movement is low.

The quartz oscillator 20 and countdown divider 21 draw negligible amounts of battery current. Almost all of the battery current is used by the stepper motor 22 which drives the gear train 23 . A typical tick pulse requires 6 milliamps of current to drive the motor's coil for 47 milliseconds, during which time the motor's rotor rotatably steps 180 degrees. The 180 degree rotation rotates the second hand 6 degrees (one second-tick).

The common alkaline AA battery 25 delivers 2.2 amp-hours to a clock which is equivalent to 28 million ticks. At one tick per second, the life of the alkaline battery 25 is about 324 days.

One important benefit of the present invention is that battery life is substantially increased. This is accomplished by programming the microcontroller 26 to stop and start the clock's hands 24 and to match stepper motor dynamics with battery chemistry. The microcontroller 26 is programmed to start and stop the hands 24 during the prescribed intervals of time and to pulse the stepper motor's coil in short intervals during each tick while using the inertia of the stepper motor's rotor between pulses to produce a reliable tick at a minimum of current.

It was determined by testing that the shortest solid pulse for producing a reliable tick in the standard movement which was tested was a 3 volt pulse for 12 milliseconds. Further tests established that the reliable tick could also be achieved by pulsing the stepper motor coil with a 3 volt pulse for 4 milliseconds to initiate rotation of the stepper motor rotor; allowing the rotor to coast for 3 milliseconds; pulsing the stepper motor coil at 3 volts for 1 millisecond; allowing the stepper motor to coast for 3 milliseconds; and pulsing the stepper motor coil at 3 volts for 1 millisecond.

Thus, by pulsing the stepper motor's coil with the microcontroller 26 in short intervals, using the inertia of the stepper motor rotor between pulses to allow the stepper motor's rotor to coast, the total time of battery current for producing the reliable tick was reduced from 12 milliseconds to 6 milliseconds. If the timing of the pulse periods and the open-circuit coast periods are matched to the rotational momentum of the stepper motor, the rotor can be made to spin , for any number of revolutions, with very little additional energy required to maintain the motion.

Heretofore, little attention has been paid by clock designers to the effect of a battery's chemistry on its performance. A lithium battery exhibits seldom appreciated recovery effects. It performs best if current is drawn in short amounts, with sufficient time intervals between uses. It requires time for its output voltage to recover. The more severely a lithium battery is used, the more time is needed for recovery. Heavy loads can render it ineffective in a matter of hours. By pulsing the stepper motor's coil with the microcontroller 26 in a series of short intervals, the life of a Panasonic CR2032 lithium battery was substantially extended in a twelve-hour clock.

The invention was evaluated by adapting a low cost Microchip Technology, Inc. PIC 12C508 microcontroller 26 to a Quartex Q84 mechanical quartz movement. The PIC 12C508 microcontroller 26 is a microprocessor together with some (or all) support peripherals (clock, memory, input/output circuits, etc.) on a single silicon chip. It is exemplary of the current state of the art. It needs no glue parts (additional components for interfacing to the outside circuit). Six of its eight pins can be used for input/output; however only five were used.

In an active mode, a built-in microcontroller clock allows execution of one million instructions per second, so real-time tasks are quickly performed. After completing a real-time task, the PIC 12C508 was programmed to sleep , drawing a current of less than one microamp, until the next task comes along. In the present invention, the tasks assigned to it are relatively simple. The PIC 12C508 microcontroller 26 spends more than 99% of its time sleeping. Average power is reduced and battery life is significantly extended over the standard movement.

The PIC 12C508 microcontroller 26 was added as shown in FIG. 2 to the Quartex Q84 movement by cutting two traces on a printed circuit board going from the countdown divider 21 to the stepper motor 22 and bringing five leads from the PIC 12C508 microcontroller 26 : two to the battery 27 , two to stepper-motor 22 , and one to the countdown divider 21 .

The 1.5V AA alkaline battery 25 of the Quartex Q84 standard movement was replaced with a Panasonic CR2032 3.0V lithium cell 27 . The 3.0V cell 27 powered both the quartz crystal oscillator 20 and the PIC 12C508 microcontroller 26 . A pulse on the line from countdown divider 21 (every two seconds) to the PIC 12C508 input pin woke up the sleeping microprocessor to perform a simple task, namely, to update the real-time clock and decide whether or not to drive the stepper motor 22 . If not, the stepper motor 22 continued to sleep until another pulse came along. When it was time to drive the stepper motor 22 , the two microprocessor output pins sent a sequence of bipolar pulses (tailored for minimum energy) to move the stepper motor's rotor a number of steps specified by a programmed function . Some of the more sophisticated functions which were evaluated required a pushbutton switch 28 to reset input and/or a diode-lamp 29 for an annunciator output.

The 3V DC, Panasonic CR2032 battery 27 which powered the crystal oscillator 20 and the PIC 12C508 microcontroller 26 is a low cost lithium coin cell 27 . Its cost has been steadily decreasing, and is now little more than the alkaline AA cell 25 . However, the lithium battery 27 has a much longer shelf life.

The shelf life of the Panasonic CR2032 lithium battery 27 is quoted as about ten years ; shelf life being the length of time over which internal leakage reduces its energy capacity to one-half the life of a factory-fresh cell. The manufacturer quotes its CR2032 battery 27 as having a capacity of 210 mah (milliamp-hours). If capacity is reduced by one half after 10 years (87,600 hrs.), leakage current in milliamps can be computed in the following manner:

In the present invention, current of the Panasonic lithium CR2032 battery 27 is used so sparingly, that the average running current is considerably less than the above leakage current. Since at least half of the capacity of a new Panasonic CR2032 battery 27 should be available after ten years, it is believed that the present invention can be used for 10 or more years with the same Panasonic CR2032 battery 27 .

The Panasonic CR2032 battery 27 is available in solder in and snap in models. The snap-in model requires battery clips and a power-on reset switch, both of which require a great deal of space and increased cost. Moreover, the pressure contacts of battery clips are not long-term reliable. One benefit of the present invention is that the low battery drain makes a solder in battery an attractive candidate for reducing cost and space as well as improving reliability.

Several clocks, which are exemplary but not limiting of the use of the present invention were evaluated. These clocks are illustrated in FIGS. 3 through 13 . In each example, an existing clock was modified by changing the dial face, adding the programmable microcontroller and programming the microcontroller to start and stop the hour and/or minute or second hand shafts in prescribed manners.

The day clock 30 is intended for retirees and other individuals who neither wear nor need a wristwatch. The hours don't matter, but the days still do. By way of example, Tuesday may be golf day or Wednesday may be reserved for dinner at the club. The clock 30 features a large display 31 (readable without glasses) of the seven days of the week.

A single hand 32 rotates at a constant rate of once per week. Heretofore, seven-day movements used special crystals and/or special gearing, and were expensive. The low cost PIC 12C508 microcontroller programmed movement, can use either the hour hand of the standard movement, driven by the microcontroller at {fraction (1/14)} normal speed; or the minute hand of the standard movement, driven by the microcontroller at {fraction (1/168)} normal speed. Using the minute hand, a battery 27 that normally lasts a year would theoretically keep the clock ticking for 168 years.

The forty-hour clock 33 is intended for persons with 8:00 A.M. to 5:00 P.M. jobs, without work on weekends. A single hand 34 starts the week at the top, at 9:00 A.M. on Monday, and heads toward a stubby line near mid-day which indicates lunch-time . The hand 34 arrives at noon, and stops for lunch. At 1:00 P.M. it starts moving again, heading for the line between Monday and Tuesday which indicates quitting-time . It arrives there at 5:00 P.M., and quits for the day. On Tuesday, Wednesday, and Thursday, the same events occur. Friday is special, a red-letter day. As a handy reminder, the lunch-line is twice as long.

The alarm day clock 35 is a derivative of an alarm clock with a standard movement, an alarm hand 36 ; an alarm set knob 37 ; a beeper (inside the case); and a snooze switch-button 38 . The clock is converted to the alarm day clock by using the hour hand 39 to point to the day. The speaker beeps on the day and at the time of day, indicated by the alarm hand 36 .

The alarm function is set by lifting the snooze button 38 in the usual manner to enable the alarm. When the hour hand 39 arrives at the alarm hand 36 , the beeper sounds to indicate an event, such as golf time . Depressing the snooze button 38 turns off the alarm.

In addition to converting the hour hand 39 into a day hand, the microcontroller 26 can be programmed to broadcast, via a speaker, messages and music, such as, find your clubs, it's golf time , followed by a tune.

Existing tide clocks require expensive planetary gearing to convert the hour hand into a tide hand which rotates once per lunar day (22 hours, 50 minutes). The PIC 12C508 microcontroller 26 can perform better. The tide has several components the strongest (lunar) tide has a period of 22 hours, 50 minutes; and the next-strongest (solar) tide has a period of 24 hours. The clock 40 , shown in FIG. 7 , operates on sideral ( real ) time, using both lunar and solar components; with the hand 41 advancing from a positive peak ( High Tide ) to a next negative peak ( Low Tide ). A reset pushbutton (not shown) on the back of the clock 40 allows the clock 40 to be reset at either full-moon or new-moon high tide.

The two-speed movement of the office clock 42 weighs the days as they should be. It provides more time on weekends, and Friday is a red-letter day. The hand 43 takes two days to traverse the top half of the dial 44 , and five days to traverse the bottom half. A reset button (not shown) on the back lets you set it at noon on any day of the week. A battery 27 inside the case has a life of at least ten years.

The seven-eleven clock 43 sleeps when you do. Its hand 44 starts at the bottom at 7:00 A.M. and advances steadily around the dial 45 . At 3:00 P.M. the hand is at the top: halfway through your day. It reaches bottom at 11:00 P.M., and stops there until 7:00 A.M. tomorrow morning. A reset button (not shown) on the back of the clock 43 allows you to set it, on the hour, at any hour of the day. A battery 27 inside of the case has a life of at least ten years.

The three-speed movement of the store clock 46 gives LUNCH and CLOSED the importance they deserve. The hand 47 covers the left quadrant between 8:00 A.M. and noon, the top quadrant between noon and 1:00 P.M., the right quadrant between 1:00 P.M. and 5:00 P.M., and the bottom quadrant between 5:00 P.M. and 8:00 A.M. A battery 27 inside of the case has a life of at least ten years.

The perpetual-calendar clock 48 has three functions date (minute hand 49 , outer indicia), month (hour hand 50 , center ring), and week day (second hand 51 , center indicia). The day hand 49 advances once per day, at midnight; and uses about 100 ticks per advance. A standard clock, at one tick per second, uses 86400 ticks per day, and the battery lasts about a year. At only 100 ticks per day, the lithium battery 27 of the perpetual calendar clock 48 has a theoretical life of 864 years. The hour hand 50 points to the month (January through December), the minute hand 49 to the date (1 thru 31), and the second hand 51 to the day of the week (Sunday through Saturday). Week days go counter-clockwise, so standard gearing can be used.

The calendar is perpetual, it recognizes leap years, the year 2000, and the year 2400, so it will never become obsolete. Since average running current is considerably less than internal leakage current, the life of the battery 27 is indeterminate and its exact value will have to be determined by actual use.

An enhancement of the calendar clock 48 is shown in the block diagram of FIG. 12. A liquid crystal display (LCD) 53 on the face 54 of the clock 48 displays reminders and notices at dates which are prescribed by the microcontroller's software. A Microchip PIC 16C55 microcontroller 26 , having 12 I/O lines, is used to drive the LCD 53 .

In the forever (everlasting) clock 55 , the second hand 56 rotates one tick per year or 60 ticks (a full revolution) in 60 years. In the alternative, the minute hand ticks 60 times per year, or 5 ticks per month, for a finer resolution. With either hand, during one complete revolution, the hands traverse 60 years.

MICROCONTROLLER SOFTWARE

The heart of the software which is common to each derivative of the standard quartz clock is a real-time update routine. Once every two seconds (when a pulse is received), the real-time clock is updated and it is decided whether to send out a tick sequence. If not, the clock goes back to sleep. If it is, a tailored tick pulse (or pulses) is sent out, and then the clock goes back to sleep.

The following is the real-time clock update routine in PIC assembly language:

At the beginning variable Seccnt ( second count ) is incremented (bumped up). If it is less than 60 (and most times it is) the program advances to label tick at the bottom. If it is finally up to 60, the program resets the microcontroller to zero and increments Mincnt ( minute count ). If it is less than 60 (most times, again), we're done.

The program advances through hour count, day count, date count, figuring the number of days per month, month count, year count, and century count.

For most cases, only the first three lines are used, updating Seccnt. Running at a clock frequency of 1 MHZ, the PIC 12C508 microcontroller executes the line in 9 microseconds, and then sleeps. Occasionally, it must complete the entire procedure before getting to tick . The worst case takes 65 microseconds. The average time per clock update is slightly more than the first 9 microseconds.

During the PIC's active time the PIC draws about 1.8 milliamps, or 1800 microamps from the battery. During sleep, current drain of the battery is about 0.25 microamps. The duty cycle, every 2 seconds, is 1800 microamps for 10 microseconds followed by 0.25 microamps for the next 1,999,990 microseconds. Excluding ticks, the average battery current drain is (1800 10 0.25 1999990)/2000000 0.259 microamps.

When a tick occurs, there is a lot of current for a relatively long time, i.e. 12 milliamps for 12 milliseconds. If this occurs once per second, by way of example in a twelve hour clock, the average current drain from ticks is ((12 ma 12 msec) (0 ma 988 msec))/1000 msec 0.144 milliamps or 144 microamps. Thus, standard-rate ticks consume battery current at 556 times the PIC. Most of the battery current is used by the stepper motor.

In FIGS. 14 and 15 a logical flow diagram is shown for a calendar (month-date-day) clock.

From the foregoing, it will be understood that my invention provides features and benefits in clocks with standard quartz movements and mechanically driven displays previously unavailable. Moreover, the invention further provides an effective, low cost means for extending the life of a clock's battery and of deriving a variety of novel clocks and features based on the standard quartz movement.

Although only several embodiments of our invention have been described it will be appreciated that other embodiments can be developed by obvious substitutions of parts and/or changes in material, shape and arrangement of parts without departing from the spirit thereof.