US2997700A - Visual indicators for low voltage apparatus - Google Patents

Description

Aug. 22, 1961 N. H. KRAMER 2,997,700

VISUAL INDICATORS FOR LOW VOLTAGE APPARATUS Filed Sept. 10. 1956 2 Sheets-Sheet 1 IN VEN TOR. NOAH H. KRAMER ATTORNEY Aug. 22, 1961 N. H. KRAMER 2,997,700

VISUAL INDICATORS FOR LOW VOLTAGE APPARATUS Filed Sept. 10, 1956 2 Sheets-Sheet 2 IL C316 T 17 IL FIG-44 D c E F United States Patent 2,997,700 VISUAL INDICATORS FOR LOW VOLTAGE APPARATUS Noah H. Kramer, Johnson City, N.Y., assignor to International Business Machines Corporation, New York,

N.Y., a corporation of New York Filed Sept. 10, 1956, Ser. No. 608,932 1 Claim. (Cl. 340-253) The present invention relates to indicating apparatus, and particularly to an arrangement for providing a light indication relative to the condition of a device having limited power available for producing such an indication.

Much use is made in the computer field of light for indicating the condition of triggers, shift registers, etc. Neon bulbs are perhaps used the most. A neon bulb will turn on with approximately ninety volts placed thereacross and off at a somewhat lower potential. They serve well where they are used in conjunction with electric discharge devices such as vacuum tubes where such a voltage is available. However, with the advent of transistor devices which use much smaller voltage values in their associated circuits, it became necessary to either use some type of indicating device unlike those used in the past or include an amplifying device in circuit between the neon and the device whose condition is to be indicated. It has been proposed to use a separate transistor amplifier for each device whose condition is to be indicated. That is, the device whose condition is to be indicated may work over a range of about forty-five volts and'the transistor amplifier can also work over a range of about forty-five volts. This arrangement permits a usable voltage of about ninety volts. While some thought has been given to the use of incandescent or filament type lights, they require more current than that available from the devic whose condition is to be indicated.

The present invention provides a light indicator for low power devices, whose condition is to be indicated, without the use of an additional transistor. Briefly, this invention comprises an element having two stable states and a response-excitation characteristic of a substantially rectangular hysteresis-loop type which may be driven back and forth between its stable states by energizing means. The device whose condition is to be indicated is coupled to said element and has a condition wherein said element will remain in one of its stable states. Visual indicator means are coupled to the energizing means so that when said element remains in said one stable state, a manifestation is provided. The arrangement is such that in the embodiments described herein, either ferromagnetic or ferroelectric devices may be used as the element and neon or incandescent bulbs used as the visual indicator means.

Accordingly, it is a primary object of this invention to provide a new and improved indicating apparatus for devices having low current and voltage characteristics.

Another object of the present invention is to furnish a new improved arrangement for indicating the condition of signal translating devices utilizing transistors or other low current and voltage devices.

Still another object of the invention is to furnish an arrangement wherein a single periodic voltage source may be used as the power source for each of a plurality of light bulbs where each bulb is under the control of a device having low voltage and current characteristics.

Other objects and advantages of the present invention will be pointed out in the following description and claim and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings Patented Aug. 22, 1961 FIG. 1 shows a schematic diagram of a first form of the invention;

FIG. 2 shows a conventional BH curve for the core which is utilized in the circuit in FIG. 1;

FIG. 3 shows a schematic diagram of another embodiment of the present invention;

FIG. 4 shows a schematic diagram of still another embodiment of the present invention;

FIG. 5 shows the VQ curve for the ferro-electric crystal which is utilized in the embodiment of the invention shown in FIG. 4.

Similar reference numerals represent similar parts throughout the several views.

Referring to FIG. 1, there is illustrated a first form of the present invention. By way of example, a bistable multivibrator or trigger is shown as the device whose condition is to be detected. This bistable device comprises two NPN junction type transistors 10 and 11. As is conventional, the emitter electrode of each transistor is connected to an N-type region and indicated with an arrow which points away from the N-type region. The base electrode of the transistor is connected to the P-type region while the collect-or electrode is connected to the other N-type region. The collector electrodes of transistors 10 and '11 are connected by way of resistors 12 and 13, respectively, to a positive source of DC potential designated +Vcc, while the base electrodes are connected to input terminals 14 and 15, respectively, and through resistors 16 and 17, respectively, to ground. The emitter electrodes of both transistors are connected to ground. To aiford the bistable action, a cross-coupling arrangement is provided comprising a first RC network 18 which couples the collector of transistor 11 with the base of transistor 10 and a second RC network 19 which couples the collector of transistor 10 with the base of transistor 11. Let it be assumed, by way of example only, that transistor 10 is normally conducting when the bistable device is storing a binary 0, i.e. the device is Off, and transistor i1 is conducting when the device is storing a binary l, i.e. the device is On.

Operation of the bistable device is such that when it is Ofl, the collector of transistor 10 will be sufficiently below the +Vcc potential to hold transistor 11 in a nonconducting state. That is, the base of transistor 11 is held so close to the emitter potential that heavy conduction is not permitted. However, a positive going pulse to terminal 15 drives the base of transistor 11 su fficiently positive to cause the transistor to conduct heavily. As this occurs, the collector of transistor 11 drops and causes transistor 10 to cease heavy conduction. Thus, the bistable device is placed in an On condition. The application of a positive pulse to terminal 14 will cause the device to turn Off.

The circuitry now to be described is used to provide a manifestation of the condition of the trigger. This circuit comprises a saturable magnetic core 20 having a first winding 21 and a second winding 22'. A source of A.C. potential 23 is connected to the plate of a diode 24, the cathode of said diode being connected to one end of winding 22. The other end of winding 22 is connected by way of an incandescent light bulb 25 to ground. The collector of transistor 11 is connected by way of a resistor 36 to one end of winding 21, the other end of the last-mentioned winding being connected to ground.

Core 20 may have a BH hysteresis loop similar to that shown in FIG. 2. Let it be assumed that the core is in the stable state 0. The positive half cycle of the voltage from A.C. source 23 is allowed to pass through diode 24 and cause current to flow through winding 22, thus saturating the core positively and placing it in its second stable state labeled 1. If it is assumed that the bistable multivibrator is Oit, i.e. transistor 11 is i a conducting state, the collector of transistor 11 will be near the +Vcc potential. Under these circumstances, sufiicient current will flow through resistor 36 and winding 21 during the negative half cycle of the A.C. source to saturate the core negatively and place it at the state labeled 0.

During the positive half cycle in the action described above, winding 22 offered a relatively high impedance to the current flow therethrough. As a result, the voltage drop across the filament of bulb 25 and the current flow therethrough are not sufficient to cause a visible light to be emitted. Thus, as long as the core is returned to its state during the negative half cycle of the A.C. source, the bulb will not light. However, if the bistable multivibrator is On, the collector of transistor 11 will be near ground potential and there will not be a suflicient voltage drop across resistor 36 and winding 21 to return core to its 0 state during the negative half cycle. Once the core 20 is placed in its 1 state, winding 22 offers a relatively low impedance to the next positive half cycle. Thus, there will be a greater current flow through the filament of bulb as well as a greater voltage drop thereacross and light will be emitted from the bulb. As long as the bistable multivibrator remains On, core 21) will remain in its 1 state and winding 22 will offer a relatively low impedance to the current fiow during the successive positive half cycles. This means that the bulb will emit light for each positive half cycle and go off during each negative half cycle. However, the frequency of the A.C. source is sufliciently high to prevent the light from being intermittent to the eye during On intervals of the bistable multivibrator.

As soon as the bistable multivibrator turns Off, the collector of transistor 11 will be sufficiently positive to return the core to its 0 state. Now, winding 22 offers a relatively high impedance to current flow during the positive half cycle of the A.C. source and the bulb 25 will not emit light.

In the circuit shown in FIG. 3, a neon bulb 31 is used in lieu of the filament type bulb 26. The neon bulb is placed in parallel with winding 22. Another variation comes about in the elimination of resistor 36 and connecting the lower end of resistor 13 through winding 21 to the collector of transistor 11. That is, winding 21 is now directly between the collector of transistor 11 and the positive source of DC. potential +Vcc. The operation of this circuit is similar to that described with respect to FIG. 1 except that current flows in winding 21 when transistor 11 is conducting rather than when it is cut ofi as was the case in FIG. 1. Since transistor 11 conducts when the trigger is On, the result is that during these times the core will be cycled back and forth between its stable states. Each time there is a change from the 0 state to the 1 state, a sufficient voltage is developed across winding 22 to cause the neon bulb 31 to emit light. When the trigger goes Ofi, transistor 11 is not conducting and therefore core 20 will remain in the 1 state. Thereafter, winding 22 otters a low impedance to the positive half cycles of the A.C. source and insufiicient voltage is developed across the neon to cause it to emit light.

Referring to FIG. 4, another embodiment of the invention is illustrated for indicating the condition of the trigger previously described. This circuit includes a ferroelectric crystal 26 which may be identical with that disclosed in Patent No. 2,717,372 granted to I. R. Anderson on September '6, 1955. The VQ hysteresis loop for such a crystal may be similar to that shown in FIG. 5. An A.C. source 27 has one side connected to ground and the other side coupled by way of a capacitor 28 to one side of crystal 26, the other side of the crystal being connected by way of the incandescent bulb 29 to ground. The collector of transistor 11 is connected by way of a resistor 30 to a point intermediate capacitor 28 and crystal 26. Capacitor 28 is used to isolate the DC. resistance of the A.C. source 27 from the ferroelectric crystal and the trigger. If an A.C. source having a relatively large D.C. resistance is used, capacitor 28 may be eliminated. When the collector of transistor 11 is essentially at ground, i.e. with the transistor conducting, the A.C. source 27 is designed to have enough voltage to cycle the ferroelectric crystal through the hysteresis loop ABCD. Each time the crystal switches 'from B to C and D to A, a change of charge occurs across the crystal and current passes through the filament of bulb 29 causing it to emit light. This light indicates that the trigger is On. When transistor 11 is not conducting, i.e. the trigger is Off, the ferroelectric crystal is biased through resistors 13 and 30 to a voltage near -i-Vcc. This voltage saturates the ferroelectric crystal and the A.C. signal operates along the line CEF where there is no great change in charge across the crystal and consequently little current flow in the filament of bulb 29. Therefore, the bulb does not emit light. Resistor 3t) limits the A.C. current flowing from power supply 27 to the trigger circuit. Ideally, such current fiow should be small.

From the above-detailed description, it will be appreciated that I have provided a new and novel indicator for devices having low voltage and current characteristics. While a bistable multivibrator has been shown as the device whose condition is to be indicated, it should be understood that there are many other types of devices with which the invention may be used. For example, it is apparent that the invention is capable of detecting whether a single transistor is in a conducting or nonconducting state. Thus, it would be suitable for use with any type of device capable of producing the necessary action to the crystal 26 in FIG. 4. The present invention can be used to indicate the condition of bistable multivibrators employing 'a single point-contact transistor. It should be further understood that the use of a bistable multivibrator employing NPN junction type transistors has been shown by way of example rather than by way of limitation. Obviously, the multivibrators could easily be constructed with PNP junction type transistors, it being necessary merely to reverse the polarity of the DC. potential and the polarity of the input pulses.

While the present invention has been illustrated as being used to produce light when the bistable multivibrator is 'On, it could just as well produce light when the device is Otf. It would only be necessary to connect element 21 or element 26 in the collector circuit of transistor 10 rather than the collector circuit of transistor 11. Alternatively, the assumption regarding when the bistable multivibrator is On and Off may be reversed.

Where it is desired to control a number of bulbs from a single source, it is but necessary to provide a plurality of the devices shown in FIGS. 1, 3 or 4 in parallel with the same source.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claim.

What is claimed is:

In an apparatus for indicating the conductive condition across the output terminals of a device having a first and second conductive condition and having relatively low voltage and current characteristics, said device being in said first conductive condition when there is a negligible potential across the said output terminals and in the said second conductive state when there is a relatively substantial potential across the said output terminals, the combination comprising: a magnetic core having a first and second stable state, said magnetic core having a substantially rectangular hysteresis-loop type responseexcitation characteristic; means including a first winding coupling the output terminals of said device to said core for producing positive magnetornotive force in said core when said device is in its second conductive condition, thereby tending to switch said core to said first stable state when said device is in said second conductive condition; said means being ineffective to produce sufiicient positive magnetomotive forces to switch said core to said first stable state when said device is in its first conductive condition; a pulse producing means for producing unidirectional voltage pulses; means including a second winding, coupling said unidirectional voltage pulse source to said core for producing, during each pulse, a negative magnetomotive force in said core greater than the positive magnetomotive force produced by said first Winding, whereby said core is switched from said first stable state to said second stable state by each pulse and reswitched to said first stable state after each pulse when said device is in said second conductive condition, also said core will remain in said second stable state it said device should revert to its first conductive condition when said core is in said second stable state; and means for indicating the voltage across said second winding.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Electronics, August 1953 (Transistor-Controlled Magnetic Amplifier) (pages 136140 relied on).

Radio-Electronic Engineering, February 1954 (Transistor Control of Magnetic Amplifiers) ( pages 13, 14, 15

20 and 30 relied on).

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