United States Patent 3831081

A miniature calculator is provided with a keyboard having a small opening which has a recessed operating switch which may be pressed by the user. The operating switch is recessed so that accidental operation of the switch is difficult. When the calculator is turned on and the button is pressed, the calculator will turn off. When the calculator is off, and the button is depressed for less than 2 seconds, the calculator will turn on. If the calculator is off and the button is depressed for longer than 2 seconds, the calculator will switch off after the two second delay, since this is an apparent accidental depression. A logic circuit controls the connection of a regulated power supply to the calculator circuitry in accordance with the condition of the push button in the keyboard. The regulated power supply is a current supply which contains circuitry which eliminates the "low end" problem wherein regulated output voltage is provided even after substantial decrease of the battery voltage. The calculator also has a display time-out circuit such that the numerals of the display flash on and off at a relatively short duty cycle of, for example, 2 percent, after the display has been on for a given time in order to conserve battery power. A low battery voltage circuit is also provided to cause the flashing of a dot in the display.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
323/282, 327/384
International Classes:
G05F1/56; G06F15/02; (IPC1-7): G05F1/56
Field of Search:
320/13 323
View Patent Images:
US Patent References:
3263156Stabilised power supply circuits1966-07-26Isaacs
2751549Current supply apparatus1956-06-19Chase

Primary Examiner:
Pellinen A. D.
Attorney, Agent or Firm:
Ostrolenk, Faber, Gerb & Soffen
The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows

1. A regulated d-c power supply circuit for a portable battery powered electrical device; said regulated d-c power supply circuit including input terminals connected to a battery power source, a series pass first transistor, output terminals connected in series with said first transistor and said battery power source and having a regulated output voltage appearing thereat; a second transistor connected to inject base current into said first transistor for controlling the conductivity of said first transistor from an off condition to a full saturation condition; a third transistor coupled to said output terminals and to said second transistor and being operable in response to the voltage of said output terminals to control the conductivity of said second transistor such that the base current injected into said first transistor tends to produce a voltage drop across said first transistor as needed to produce a given regulated voltage output at said output terminals; an on-off control circuit for turning said second transistor on and off thereby to turn said first transistor off in the off condition of said control circuit, and for permitting said second transistor to regulate the operation of said first transistor in the on condition of said control circuit; said on-off control circuit comprising a reset flip-flop circuit means connected between said battery and said second transistor, and means for operating said flip-flop circuit means between a set condition and a reset condition which respectively permits and prevents connection between said battery and said electrical device; said means for operating said flip-flop circuit means including a mechanical switch whereby closing of said switch causes said flip-flop circuit means to reset from a set condition and causes said flip-flop circuit means to set from a reset condition.

2. The power supply of claim 1, wherein said electrical device is contained within an enclosing housing; said housing having an aperture therein; said on-off control circuit including a push button type switch means, whereby application of pressure to said push button type switch means switches said electrical device between first and second operational conditions; said push button type switch means being recessed within said aperture and accessible through said aperture; said aperture having a diameter sufficiently large to enable operation of said switch means by a human finger; said switch means being recessed in said aperture to prevent inadvertent operation of said switch means.


This invention relates to a miniature calculator and more specifically relates to a novel on-off control circuit for a miniature calculator in combination with a mechanical construction for the calculator housing which eliminates accidental actuation of the calculator display and which eliminates troublesome and expensive components of the prior art miniature calculators. More specifically, and in accordance with the invention, a novel on-off circuit is controlled by a push button switch which is placed at the bottom of a relatively deep opening in the casing. This on-off circuit is used to turn on and off a novel power supply which is used to drive the calculator circuit.

While the novel on-off circuit of the present invention is described herein primarily in connection with miniature calculators, it will be understood by those skilled in the art that the novel circuit and structure has general application for the control of any type of electrical circuit arrangement.

Miniature calculators and other similar types of devices are commonly turned on and off by a conventional slide switch which is operated by an operating handle which usually projects above the surface of the device housing. It has been found that these switches are relatively expensive and are a serious cause of device malfunctioning because of contact problems. Moreover, since the switch often projects above the surface of the housing, the switch device is subject to damage by inadvertently brushing objects across the surface of the housing and is subject to accidental turning on as when a miniature calculator is loaded into a suitcase or other storage container. This would then cause a continuous unintentional battery drain.

In accordance with the present invention, a novel on-off circuit is provided for devices such as miniature calculators, where the on-off circuit is operated by a push-type switch. The control circuit is such that, by pressing the switch a first time, a circuit which is on will be turned off. By pressing the button a second time, a circuit which is off will be placed on. If, however, the button is held closed for more than two seconds (or any other desired delay time), then the circuit will again automatically switch off since it can be presumed that holding down of the button for this relatively long time is due to accidental causes.

A novel mechanical construction is also provided in combination with this novel circuitry whereby the button to be operated in a push-push manner is recessed below the flush surface of the calculator or other device housing surface, and is accessible through a relatively small opening. Therefore, the operator must intentionally operate the push-push type control and it is difficult to operate the control button accidentally.

Further in combination with this novel circuitry, there is provided a novel regulated power supply which avoids the common "low end" problem encountered with miniaturized, inexpensive power supplies for small devices, such as miniature calculators, whereby a regulated output voltage can be obtained from a relatively inexpensive circuitry over a relatively wide range of input battery voltage. Once, however, the input battery voltage decreases below some minimum value, the current supply circuit is switched off.


FIG. 1 is a front view of a miniature calculator which uses the present invention.

FIG. 2 is a side plan view of the calculator of FIG. 1.

FIG. 3 is a cross-sectional view through a portion of the calculator of FIG. 1 to illustrate the manner in which the on-off switch, which is a push-push type switch, is depressed below the surface of the calculator housing.

FIG. 4 is a schematic block diagram of the operating circuit of the calculator of FIGS. 1 and 2.

FIG. 5 is a circuit diagram which shows the battery power supply circuit and the regulated power supply circuit of FIG. 4.

FIG. 6 shows the on-off keyboard control switch of FIG. 4.


Referring first to FIGS. 1 and 2, there is shown a miniature calculator which is contained within a plastic housing 10. Housing 10 contains a window 11 which has a numerical display therein of conventional type, and which could consist, for example, of a plurality of LED devices which present a digital display having, for example, nine positions. Any desired display can be used in connection with the present invention.

A keyboard 12 is then provided, shown in FIG. 1, which can be a conventional keyboard in all respects with the exception of the on-off control 13. Thus, the keyboard may contain the conventional button input keys which can be depressed in order to enter various numerals or functions of conventional nature into the calculator circuitry, which is contained within the housing 10 and which result in calculation results to be displayed in the display 11.

While the keyboard members of keyboard 12 may be conventional buttons, they may also be formed of bevelshaped openings which lead to a conductive flexible member which is depressed when one of the exposed numeral or operation areas is pressed by the operator's finger in order to deliver a suitable input into the calculator circuitry associated with the particular key area which is operated.

FIG. 3 schematically illustrates this type of keyboard, where, for example, an opening 20 for numeral 7 in the keyboard 12 of FIG. 1 is shown to have a bezel shape.

A conductive member 21 (or other suitable switching means) is contained at the bottom of bezel-shaped opening 20 which, in a manner unrelated to the present invention, is responsible for delivering a signal to the computer circuitry indicating that the numeral 7 has entered into the calculator.

In accordance with an important feature of the present invention, the on-off control 13 of keyboard 12 is formed of a push button type switch as contrasted to a sliding switch, where the push button type switch has its operating member contained beneath the outer surface of the keyboard or housing, and is depressed within a relatively small opening shown as opening 25 in FIG. 3, beneath the flush outer surface 26 which surrounds the opening 25.

Any conventional switching mechanism, schematically illustrated as the member 27, is recessed to the base of opening 25 and could, for example, be a conventional push button-type switch or, if desired, could be a continuation of the conductive mesh used for actuating the entire keyboard structure where such a keyboard construction is selected.

The term push button switch is used here to indicate a type of switching circuit which, when pressed, will cause an output from a power supply to change state. Thus, if the computer circuit is on and the switch is operated, the computer power supply will be turned off. Conversely, if the computer circuit is off and the switch is operated, the power supply will turn on. In accordance with a further feature of the invention, and as will be later seen, if the power supply is off and the switch is pressed closed for a time period longer than some predetermined time, for example, two seconds, the power supply will again turn off since it is likely that the button has been depressed and is held depressed by accidental means.

By recessing the push-button switch to the base of a relatively deep hole, it becomes unlikely that the switch can be unintentionally operated. By way of example, on-off switches of the prior art have been accidentally operated when devices were placed in a drawer or a briefcase, and other stored objects are pressed against the switch. This then causes a continuous and unintentional drain on the relatively small capacity battery provided with the device. Moreover, it is possible to damage the prior art switching handle which conventionally projects outwardly and above the surface of the device housing.

In accordance with the present invention, it has been found that a finger-operated push-button switch is well protected against accidental operation and is still conveniently operable by the human finger when the opening 25 has a diameter of about 3/8 of an inch, with the switch button surface recessed below the outer surface of the housing by about 0.062 inches.

It is further possible to make it easier for the user to find the on-off switch location in an easy manner by placing the entire on-off switch area on a bezel 30 shown in FIG. 1, which allows the user to quickly locate a raised or a depressed surface by feel and without having to look at the calculator. The bezel surface can, for example, be raised by about 0.010 inches over the major portion of the keyboard surface.

The calculator circuitry which is contained within the housing 10 and which is turned on and operated by delivering appropriate information into the keyboard 12 is schematically shown in FIG. 4. Referring to FIG. 4, there is schematically shown the input power source which can consist of a battery or a-c to d-c power converter and charger 40. The input power source 40 is controlled by the on-off keyboard control system 41 which will be described hereinafter in connection with FIG. 6, and which is controlled from the push-button switch 27 in the keyboard 12 of FIGS. 1 and 3. Note that in FIG. 4 the keyboard 12 is shown in block diagram and is coupled by the dotted line 42 to the on-off keyboard control circuit 41.

The on-off keyboard control circuit 41 is then connected to control the output of regulated power supply 42 in that circuit 41 turns the regulated power supply on and off. Power supply 42 then drives the main calculator circuitry 43 and display 44, which may be a conventional LED display 11 in FIG. 1. The regulated power supply 42 may also be connected to a low battery voltage display 45 which will cause the flashing of a numeral or segment in display 44 to warn the user that the battery in power supply 40 needs replacement or charging.

A display time-out circuit 46 is also provided which is connected to display 44 and will cause the display 44 to flash at a relatively low duty cycle, for example, on for 2% of the time, after the display has been presented for a given time. This feature conserves battery power when the user fails to turn the display off after it has been presented for a given period of time.

The schematically illustrated battery or ac/dc power source 40 is shown in FIG. 5 as including a conventional chargeable battery 50. Note that battery 50 could be a disposable battery.

The negative or ground side of battery 50 is connected to a grounded bus and to a terminal 51 in a conventional jack 52 which contains a switch 53 connected to the positive side of battery 50. An output terminal 54 is then used as a source of battery voltage for other components of the circuit used for the calculator and is derived directly from the battery 50 and is unregulated.

All terminals in the circuits to be described hereinafter which are connected to the terminal 54 are identified by a +7H to indicate that the potential at the terminal is unregulated battery voltage (normally at 7 volts). Regulated voltage from the power supply is designated as +7 V to indicate that this is 7 volts regulated. Thus, the +7 H voltage terminals may vary depending upon the state of charge of the battery and of the current being drawn at a particular instant which might regulate the battery voltage while the voltage +7V will be accurately held to 7 volts, within the capability of the battery to have a given minimum output voltage.

FIG. 5 also shows the power supply regulator circuit which produces an output at terminal 55 which is +7V or a highly regulated output of 7 volts which is relatively constant over a wide variation of input battery voltage. This output at terminal 55 is used to drive other portions of the computer circuitry, and will appear in response to the condition of the on-off control circuit 41 of FIG. 4 which is shown in detail in FIG. 6.

The operation of the regulated supply circuit of FIG. 5 will be described more fully hereinafter, it being understood for the present that the circuit will produce an output operating voltage for the calculator in response to the appearance at its input control terminal 60 of voltage output from the circuit of FIG. 6, and will be switched off in response to the disappearance of the voltage signal at terminal 60.

FIG. 6 shows the novel on-off control circuit of the invention which is operated under the control of a switch 70, which generally can be any desired type switching device, but preferably is a push button-type switch. The output terminal 60 is shown in FIG. 6 and the voltage at this terminal will ultimately control the turning on and off of the calculator by turning on and off its power supply from the circuit of FIG. 5.

The circuit of FIG. 6 contains four gates, A, B, C and D, which are integral components of a standard CMOS logic gate, type number CD4011AE. The various pins of the gates A, B, C and D are numbered 1 to 14 as shown. As will be seen more fully hereinafter, gates A and B are arranged to form a reset flip-flop (commonly termed a latch) while gates C and D provide the logical input to gates A and B to set or reset the flip-flop condition.

In FIG. 6, the schematically illustrated push-button switch 70 is connected in series with terminal 71, which is connected to the battery voltage +7 H and in further series with an input resistor 72. The right-hand end of resistor 72 is connected to a differentiator circuit consisting of resistor 73, capacitor 74 and resistor 75, where, as will be seen hereinafter, this differentiator circuit allows the production of an only momentary set command for the flip-flop whenever the push button 70 is closed. Thus, even if the push button 70 is held depressed for an extended period of time, as due to its accidental depression, only one pulse will be applied to gates C and D, as will be later described in more detail.

The reset side of the flip-flop is directly coupled to the push button 70 through the diode 76, such that any input created by the closing of the push button 70 will be indefinitely valid. Thus, if the push button 70 is held down continuously, the reset mode of operation will ultimately predominate over the set mode of operation which might have been induced by the single pulse passed by the differentiator capacitor 74.

A reset delay circuit is then formed by diodes 77, 78, resistors 79 and 80 and capacitor 81. The terminals 82 and 83 of this circuit are connected to the +7H battery terminal. Capacitor 81 is also connected to the resistor 84 which is, in turn, connected to terminal 83. The reset delay circuit described above forms a one-shot type of circuit which prevents reset of the flip-flop before an operator's finger can be removed from the push button 21.

The operation of the circuit of FIG. 5 is such that if there is to be an output signal on terminal 60, it is necessary for the flip-flop to be set. When the flip-flop is reset, there is no signal at terminal 60, so that the power supply to be described hereinafter in connection with FIG. 5 is cut off.

The circuit of FIG. 5 will operate as follows:

A. If the flip-flop is in the reset condition and there is no output at terminal 60 and the push button 70 is pressed closed for less than 2 seconds, the flip-flop will set and remain set. Thus, an output voltage will appear on the terminal 60 which ultimately will turn on the regulated power supply of FIG. 5.

B. If the flip-flop is in the set condition, which corresponds to an on condition for the calculator, and the push button 70 is pressed either momentarily or permanently, the flip-flop will reset and remain reset so that there will be zero output at terminal 60 and the power supply for the calculator is turned off.

C. If the flip-flop is in the reset condition and push button 70 is pressed for more than two seconds, the flip-flop will first set but will, after a two second time delay, reset and remain reset. Thus, if the push button 70 is unintentionally or accidentally closed for more than two seconds, the calculator will not unintentionally be turned on for more than the two second time delay.

In the operation of the circuit of FIG. 5, it was pointed out previously that resistors 73 and 75 and capacitor 74 form a differentiator which insures only a momentary set command to the flip-flop after the button 70 is closed. The two second delay is formed by the delay circuit including capacitor 81, whereby the initial pulse through capacitor 74 will cause the reset flip-flop to set but, if the button is still depressed at the end of the two seconds, the capacitor 81 will cause the now set flip-flop to again reset. In other words, the capacitor 81 acts as a two-second inhibiting circuit which would prevent the reset of the flip-flop for a two-second period. It is only if the button is released at the end of this two-second period that the capacitor 81 and its associated circuitry do not cause the resetting of the set flip-flop. Thus, at the end of two seconds, the space of the button 70 is interrogated by the diode 76. If the button is still depressed, the diode 76 would be back-biased at the end of the two-second delay, so that the voltage on pin 2 of gate D goes to a logic 1 to initiate reset of the flip-flop. If, however, the button was released before the end of the two-second time delay, the diode 76 would be forward-biased to prevent the appearance of a voltage at pin 2 so that the flip-flop remains set.

It should be understood that the specific circuit shown in FIG. 6 has extremely wide application to any electronic switching function for producing an output or no output at terminal 60, and the novel circuit of FIG. 6 is not limited to its use in connection with an electronic calculator. In this regard, it is also extremely useful, but not necessary, that the switch of FIG. 6 be recessed beneath an opening in a flat surface, so that it will not be accidentally actuated. Note, however, that other switching structures can be used in the FIG. 6 circuit and that the novel function of the circuit of FIG. 6 would prevent the inadvertent turning on of a circuit being controlled, if the switch is accidentally closed.

One satisfactory circuit which performs the function stated above using the circuit diagram of FIG. 6 used the following components:

CIRCUIT OF FIG. 6 Resistors 72 100K 73 2.2 MEG 75 470K 79 2.2 MEG 80,84 10 MEG Capacitors 74 0.1Mf, 12V 81 0.01Mf, 35V Solid State Components Gates A, B, C & D CMOS Logic Gate CD4011AE Diodes 76, 77 & 78 1N4148

Turning next to FIG. 5, there is shown the novel regulated power supply which will be turned on and off in response to the appearance of a voltage at terminal 60. More specifically, when the flip-flop of FIG. 6 is set, the voltage at terminal 60 will rise to +7H to turn on the power supply. When the flip-flop of FIG. 6 is reset, the voltage at terminal 60 will decrease substantially to zero.

The regulated power supply of FIG. 5 contains a series pass transistor 100 connected from the positive terminal 54 to the regulated output terminal 55 which produces a regulated output of 7 volts for the operation of the various calculator circuits.

A capacitor 101 is connected between terminal 55 and ground. Transistor 100 has its base connected to amplifying transistor 102 which, as will be later seen, can drive transistor 100 to saturation. The emitter of transistor 102 is connected through resistor 103 to ground. The base of transistor 102 is controlled by the output of transistor 104, which has its emitter connected to ground through resistor 105. A voltage divider consisting of resistors 106 and 107 are connected across terminal 55 and ground and their junction is connected to diode 108 and capacitor 109 which control the input to the transistor 104.

The base of transistor 102 is also connected to the terminal 60 through the diode 110 and through resistors 111 and 112. Resistors 111 and 112 are also connected to the zener diode 113 as shown.

As pointed out previously, the novel circuit of FIG. 5 avoids the so-called low end problems of inexpensive regulated power supplies of the type necessary for miniaturized calculators. This problem was introduced because the series pass transistor elements required at least a 1 volt drop thereacross, even when the battery voltage was outside of the regulation range. In the circuit of the present invention, if the battery voltage at terminal 54 drops below some given value, the transistor 100 saturates and thereby causes a minimal drop, so that transistor 104 turns off. All current from resistor 111 will then go into the base of transistor 102. This current is then amplified by transistor 102, thus driving the base of transistor 100 to saturation, and substantially eliminating the series pass transistor drop.

During the normal operation of FIG. 5, and assuming that the battery voltage is within its proper limits, the transistor 100 will normally divert more or less current from transistor 102. Thus, if the output voltage is too low, transistor 104 will turn off until, eventually, the transistor 100 will connect the battery directly to the output terminal 55 without any drop. Note that, for some output to be produced at terminal 55, voltage must be present at terminal 60. Thus, if no voltage appears at terminal 60 due to the off state of the circuit of FIG. 6, there is no current in resistor 111 to be amplified, so that the transistor 100 turns off.

A satisfactory circuit which produced acceptable operation and which was connected as shown in FIG. 5 used the following components:

CIRCUIT OF FIG. 5 Resistors 103 100 Ω 105 680 Ω 106 30K 107 10K 111 11K 112 1K Capacitors 101 4.7Mf, 16V 109 0.1Mf, 12V Solid State Components Transistor 100 EN2907 Transistor 102 538276 Transistor 104 538276 Diode 108 1N4148 Diode 110 1N270 Zener Diode 113 1N755A

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention will be limited, not by the specific disclosure herein, but only by the appended claims.