AUDIO COMPASS
United States Patent 3786571
The audio compass includes a first polarized transparent sheet affixed to a magnetic needle of a magnetic compass, and second and third polarized transparent sheets affixed to a graduated compass ring rotatably mounted on a housing for the magnetic compass and having their planes of polarization offset from each other by an angle which is bisected by the polarization plane of magnitude first sheet when the zero mark of the compass ring is set at north. Light from a first light source shines through the first and second sheets on a first photocell, and light from a second light source shines through the first and third sheets on to a second photocell. Circuit means coupled to the photocells produces first and second audio tones of different frequencies interrupted at rates related to the intensity of the light received by the first and second photocells respectively. A shift of the second and third sheets to the left or right from the north position increases the light received by one of the photocells and decreases the light received by the other photocell to produce a tone which is interrupted at a rate related to the change of the light received by one of the photocells. Thus, when the audio compass is mounted in a boat and the compass is set for a particular heading, a deviation of the boat to the left of that heading will produce a tone of one frequency, and a deviation of the boat to the right of that heading will produce another tone of a different frequency. The rate of the interruptions or modulations in the tones indicates the magntidue of the deviation.
US Patent References:
MEANS TO DETECT AMOUNT AND DIRECTION OF SHAFT ROTATION
White - October 1969 - 3474255
MEANS TO DETECT AMOUNT AND DIRECTION OF SHAFT ROTATION
White - October 1969 - 3474255
Application Number:
05/284904
Publication Date:
01/22/1974
Filing Date:
08/30/1972
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
359/501, 116/204, 250/204, 33/349, 340/328
International Classes:
G01C17/26; G01C17/00; G01C17/26
Field of Search:
33/363K,348,349,328 250/225,204,220
Primary Examiner:
Hull, Robert B.
Assistant Examiner:
Stearns, Richard R.
Attorney, Agent or Firm:
Oltman, And Flynn
Claims:
Having thus described my invention, I claim
1. An audio compass comprising:
2. The audio compass as claimed in claim 1 in which said circuit means includes first and second oscillator means for producing said first and second tones respectively.
3. The audio compass as claimed in claim 2 in which said circuit means includes first and second enabling circuits responsive to signals from said first and second photocells respectively for enabling only one of said oscillator means at a time corresponding to a left or right displacement of said first sheet with respect to said zero mark.
4. The audio compass as claimed in claim 3 in which said circuit means includes first and second signal producing means coupled to said first and second photocells respectively for producing left and right error signals proportional to a change in the light received by the photocells when the magnetic needle and said first sheet are displaced from said zero mark, and first and second modulating means responsive to said left and right error signals to modulate said first and second oscillator means with pulses providing said amplitude modulations of said first and second tones.
5. The audio compass as claimed in claim 4 in which said circuit means includes electroacoustic transducer means for making said first and second audio tones audible.
6. An audio compass comprising:
7. The audio compass as claimed in claim 6 including enabling circuit means coupled between each of said photocells and said first and second oscillator means for enabling the oscillator corresponding to only one of said photocells.
8. The audio compass as claimed in claim 7 in which the enabled oscillator corresponds to the photocell receiving an increasing intensity of light when said first sheet is displaced.
1. An audio compass comprising:
2. The audio compass as claimed in claim 1 in which said circuit means includes first and second oscillator means for producing said first and second tones respectively.
3. The audio compass as claimed in claim 2 in which said circuit means includes first and second enabling circuits responsive to signals from said first and second photocells respectively for enabling only one of said oscillator means at a time corresponding to a left or right displacement of said first sheet with respect to said zero mark.
4. The audio compass as claimed in claim 3 in which said circuit means includes first and second signal producing means coupled to said first and second photocells respectively for producing left and right error signals proportional to a change in the light received by the photocells when the magnetic needle and said first sheet are displaced from said zero mark, and first and second modulating means responsive to said left and right error signals to modulate said first and second oscillator means with pulses providing said amplitude modulations of said first and second tones.
5. The audio compass as claimed in claim 4 in which said circuit means includes electroacoustic transducer means for making said first and second audio tones audible.
6. An audio compass comprising:
7. The audio compass as claimed in claim 6 including enabling circuit means coupled between each of said photocells and said first and second oscillator means for enabling the oscillator corresponding to only one of said photocells.
8. The audio compass as claimed in claim 7 in which the enabled oscillator corresponds to the photocell receiving an increasing intensity of light when said first sheet is displaced.
Description:
BACKGROUND OF THE INVENTION
Many types of compasses have been proposed, but many of them require that the operator of the boat or other vehicle in which the compass is provided watch the compass to detect when the boat has deviated from the desired course. It would be desirable to have a relatively simple compass which would produce audible sounds that would indicate a deviation of a boat or other vehicle from a desired course without requiring the operator to watch the compass. Such a compass would be particularly useful on small boats where the crew, or sometimes a single sailor, is often too busy to watch a visual compass.
SUMMARY OF THE INVENTION
The present invention is an audio compass in which light sensed by devices such as photocells is controlled by polarized transparent sheets associated with a magnetic compass, and circuit means is responsive to changes in the electrical characteristics of the photocells to produce audible tones of different frequencies. A first tone of one frequency indicates a deviation of the compass or boat to one side of a desired heading, and a second tone of a different frequency indicates a deviation of the compass or boat to the other side of the desired heading. The tones are interrupted or modulated at a rate related to the magnitude of the deviation. Thus, by listening to the tone, an operator can tell when the boat deviates from the desired heading and the boat can be steered back onto that heading. In the preferred embodiment, no tone is produced when the boat is on the desired heading, although this condition could be indicated by still a third tone.
Accordingly, it is an object of the present invention to provide an audio compass which indicates left and right deviations from a desired heading of a boat by producing first and second tones of different frequencies corresponding to the left and right deviations.
Another object of the present invention is to generate the tones by controlling light received by photocells of the audio compass.
A further object of the invention is to accomplish the controlling of the light with polarized sheets through which the light shines.
Another object of the invention is to interrupt or modulate the tones at a rate which is related to the magnitude of the deviation of the compass or the vehicle from a desired heading.
Among the other objects of the invention are to provide an audio compass which is relatively simple and straightforward; which is reliable in operation; in which the parts cooperate efficiently and uniquely; and which can be produced economically on a practical manufacturing basis.
Other objects of this invention will appear from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly cut away, showing an audio compass in accordance with one embodiment of the invention;
FIG. 2 is a vertical sectional view taken along Line 2--2 of FIG. 1 and looking in the direction of the arrows;
FIG. 3 is a plan view similar to FIG. 1, but showing how a compass ring and two polarized sheets of the compass are rotated to set the audio compass at a desired heading;
FIG. 4 is a reduced plan view illustrating a deviation of the compass to the right of a desired heading;
FIG. 5 is a reduced plan view illustrating a deviation of the compass to the left of a desired heading; and
FIGS. 6, 7 and 8 show schematically successive portions of the electrical circuit in the present invention for producing an audible signal in response to a deviation of the compass from the desired heading.
Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.
DETAILED DESCRIPTION
The audio compass of the illustrated embodiment of the invention includes a magnetic compass 10 shown in FIGS. 1 through 5 and electronic circuit means shown in FIGS. 6 through 8. Referring first to FIGS. 1-5, the magnetic compass 10 has a housing 12, which in this embodiment is a bowl, and a transparent face plate 14 which covers and seals the top of the housing 12. The housing 12 and the face plate may contain a compass fluid on which certain components float as will be described. The face plate 14 may be threaded at 16 to screw into matching threads in the upper lip at the perimeter of the housing 12.
The magnetic compass 10 has a magnetic needle 18 for pointing north in accordance with conventional magnetic compass techniques. The needle 18 is mounted on and affixed to a polarized transparent sheet 20 which is pivoted on a stem 22 such that the sheet 20 and the needle 18 can swing freely about the stem 22. In this embodiment, the stem 22 extends upward from a dome 24, and the bottom of the dome is affixed to the housing 12. As indicated by the vertical lines 26 in FIG. 1, the plane of polarization of the transparent sheet 20 is permanently aligned with the longitudinal direction of the magnetic needle 18.
A compass ring 28 graduated in degrees is rotatably mounted on the circular lip 30 at the top of the housing 12 so that the ring 28 can be rotated through 360° and will stay at any selected position. In the illustrated embodiment, the ring 28 has a slot at 32 which receives the perimeter of a circular ring 34 which is fastened to the lip 30 as with screws 36.
Fixed to the ring 28 are two polarized transparent sheets 38 and 40 which are concentric with each other. Sheet 40 is a disc located at the center of ring 28, and sheet 38 is a ring surrounding and attached to disc 40. Ring-shaped sheet 38 is also attached to ring 28. The attachment of the sheets 38 and 40 to each other and to the ring 28 may be accomplished with adhesive material.
As indicated by the lines 42 and 44 in FIG. 1, the planes of polarization of the sheets 38 and 40 are offset from each other by an angle which is bisected by the polarization plane 26 of the sheet 20 when the zero degree mark of the compass ring 28 is set at north as in FIG. 1. In the illustrated embodiment, the polarization plane represented by the lines 42 for sheet 38 is offset 45° clockwise from the zero degree mark and the polarization plane represented by the lines 44 for sheet 40 is offset 45° counterclockwise from the zero degree mark. With the zero degree mark set at north,the two polarization planes 42 and 44 are bisected by the polarization plane 26 which is aligned with the north direction.
The sheet 20 floats on compass fluid contained in the housing 12. The housing 12 is ordinarily supported by gimbals of a gyroscope to keep it level.
A light source 46 is contained in the dome 24, and light from this source shines upward through the stem 22 and around the stem 22 which may be transparent. The rest of the dome 24 may be opaque. This light shines through sheet 20 and also shines through the central sheet 40. A photocell 48 is mounted on a bracket 50 which is attached to the housing 12 in a position to receive the light from the source 46. The amount of light received by the photocell 48 is related to the orientation of the sheets 40 and 20 as will be explained further.
Another light source 52 is mounted inside a dome 54 which has a transparent window 56. The rest of the dome is opaque. Light from the source 52 shines through the window 56 and through the sheet 20 as well as the outer ring-shaped sheet 38 which is affixed to the compass ring 28. Another photocell 58 is mounted on the bracket 50 in a position to receive the light from the source 52. The amount of light received by the photocell 58 is controlled by the orientation of the sheets 38 and 20 as will be explained further.
The magnetic compass 10 is ordinarily mounted in a boat or other vehicle. The compass is utilized to assist the operator, which may be the helmsman, to steer the boat on a desired heading. The heading is set in a manner illustrated in FIG. 3. In FIG. 3, the compass ring 28 has been rotated clockwise to a heading of 315°. After this heading has been set, the boat is turned counterclockwise to bring the zero degree mark back to the north heading which will place the compass in the condition illustrated in FIG. 1. Thus, as long as the zero degree mark is kept at the north heading, the boat will be on course. To assist the helmsman in accomplishing this, the circuit means illustrated in FIGS. 6-8 is provided. This circuitry is coupled to the photocells 48 and 58, and it produces first and second audio frequency tones of different frequencies which are interrupted or modulated at rates related to the intensity of the light received by the two photocells 48 and 58. A shift of the sheets 40 and 38 to the left or right from north position shown in FIG. 1 increases the light received by one of the photocells and decreases the light received by the other photocell. As will be explained, this produces a tone which is interrupted at a rate related to the magnitude of the change in light received by one of the photocells. In the illustrated embodiment, it is the photocell which receives an increased amount of light that produces a tone.
Referring to FIG. 6, the photocells 48 and 58 are visible at the left side of the drawing. Photocell 48 receives more light when the compass rotates to the right of the north heading as illustrated in FIG. 4 because the plane 44 tends to become more nearly aligned with the plane 26, so more light passes through sheets 40 and 20 to the photocell 48. Photocell 58 receives more light when the compass rotates to the left of a north heading as illustrated in FIG. 5 because the plane 42 becomes more nearly aligned with the plane 26 so that more light passes through sheets 38 and 20 onto photocell 58. Conversely, less light reaches photocell 58 when the compass rotates to the right, and less light reaches photocell 48 when the compass rotates to the left. It will be understood that this relationship could be reversed if desired.
The photocells 48 and 58 are connected to (or may be considered part of) two signal producing means 100 and 102. The signal producing means 100 includes a voltage divider 104 with resistors 106, 108 and 110 connected between supply terminals 112 and 114, together with amplifying transistors 116 and 118 and resistors 120 and 122. The signal producing means 100 produces a right error signal at output 124.
Signal producing means 102 includes a voltage divider 126 consisting of resistors 128, 130 and 132 connected between supply terminals 134 and 136, together with amplifying transistors 138 and 140 and resistors 142 and 144. A left error signal is produced at the output 146 of signal producing means 102.
The error signals appearing at outputs 124 and 146 are proportional to the change in the light received by the photocells 48 and 58 when the magnetic compass 10 deviates from the north setting shown in FIG. 1. The porportionality of these signals to the change in light is effective only through a certain range which is represented by the positive range R and the negative range -R illustrated in FIGS. 4 and 5. The illustrated range is arbitrary, and some other effective range could be utilized.
The signal output 124 is connected by line 148 to the input 150 of a variable frequency astable multivibrator circuit 152. Similarly, the signal output 146 is connected by line 154 to the input 156 of another variable frequency astable multivibrator circuit 158. The multivibrator circuit 152 is connected to a right channel oscillator circuit 160, and the multivibrator 158 is connected to a left channel oscillator circuit 162. Oscillator 160 may have a stable frequency of 1000 cycles per second, by way of example, and oscillator 162 may have a stable frequency of 400 cycles per second, by way of example. Oscillator 160 has an enabling transistor 164 which is connected through transistors 166 and 168 to a line 170 which leads back to a Schmidt trigger circuit, the input 174 of which is connected to the error signal output 124. Similarly, oscillator 162 has an enabling transistor 176 which is connected through transistors 178 and 180 to a line 182 which leads back to a Schmidt trigger circuit 184, the input 186 of which is connected to the error signal output 146. In operation, the error signal appearing at output 124 activates the Schmidt trigger circuit 172 which, in turn, feeds an enabling signal via line 170 to the enabling transistors 168, 166 and 164 to activate the oscillator 160. The oscillator 160 is operative only when the error signal appearing at output 124 increases in magnitude. On the other hand, when the error signal appearing at output 146 increases, Schmidt trigger circuit 154 is activated to feed an enabling signal via line 182 to the enabling transistors 180, 178 and 176 which turn on the oscillator 162. The oscillator 162 is operative only when the error signal appearing at output 146 increases in magnitude.
The right channel error signal, which is fed via line 148 to the multivibrator circuit 152, causes the flip-flop transistors 188 and 190 of the multivibrator to turn on alternately. Pulses produced by the flip-flop transistors 188 and 190 appear at line 192 and these pulses are fed to the enabling transistor 166. The pulses cause the operation of the oscillator circuit 160 to be interrupted or modulated at the repetition rate of the pulses. This pulse repetition rate is proportional to the magnitude of the right channel error voltage appearing at input 150 of the multivibrator circuit 152.
Multivibrator circuit 158 and tone oscillator 162 operate in the same manner. The left channel error signal appearing at input 156 causes flip-flop transistors 194 and 196 to turn on alternately. These transistors produce pulses at line 198 which are fed to the enabling transistor 178. The pulses cause the tone oscillator 162 to be interrupted at a rate which is proportional to the repetition rate of the pulses. The pulse repetition rate is proportional to the magnitude of the left channel error voltage fed to multivibrator circuit 158.
The modulated tone signals are delivered from the oscillators 160 and 162 at outputs 200 and 202. These tone signals are fed via a common line 204 to the audio output circuit 206 illustrated in FIG. 8. The audio output circuit includes an audio amplifier 208 which supplies the modulated tones through a transformer 210 to a transducer 212 which might be a loudspeaker or earphones by way of example.
The audio compass has a "silence" or "null" zone in which no signals are produced. This zone occupies a predetermined number of degrees left and right from the north heading. The "null" zone might occupy only plus or minus one degree, by way of example, but by adjusting the potentiometer 214, the "null" zone could be increased to say plus or minus five degrees. Assuming that the "null" zone is set at five degrees the right error signal would start producing modulated tones when the compass rotates five degrees to the right or clockwise as illustrated in FIG. 4, and the left error signal would start producing modulated 400 cycle tones when the compass has rotated five degrees to the left as illustrated in FIG. 5. The symbols E and -E in FIGS. 4 and 5 respectively, indicate the error or deviation from the desired heading. In FIG. 4, the error E and in FIG. 5 the error -E are right 5 degrees and left five degrees respectively. The error E would produce a 100 cycle tone interrupted at a rate proportional to the magnitude of the error, and the error -E would produce a 400 cycle tone interrupted at a rate proportional to the magnitude of the error.
Switches 215 and 216 are on-off switches. Potentiometer 218 provides a volume adjustment. Potentiometer 220 provides a zero adjustment. The light sources or lamps 46 and 52 are connected to the potentiometer 220.
It will be recognized that the individual circuits of the system are standard. The Schmidt trigger circuits 172 and 184 may be in the form integrated circuits 222 and 224 provided with amplifying transistors 226, 228, 230 and 232. The transistors 188, 190 may have input transistors 234 and 236, and the transistors 194 and 196 may have input transistors 238 and 240. Right channel tone oscillator 160 includes transistors 242 and 244 and left channel tone oscillator 162 includes transistors 246 and 248. The audio amplifier 208 in FIG. 8 may be an integrated circuit. The various biasing components of the circuitry are standard and will not be described in detail.
CONCLUSION
Thus, the invention provides an audio compass which is simple and reliable in operation. If the heading error increases, one photocell output increases and the other photocell output decreases.
The signal producing circuits receive the photocell outputs and cause one of the two Schmidt trigger circuits to fire. The increasing photocell output causes the corresponding oscillator to be enabled, and causes the appropriate astable multivibrator circuit to increase its pulse repetition rate according to the magnitude of the heading error. The multivibrator output gates the corresponding audio tone oscillator into the audio amplifier, which in turn, drives the output loudspeaker. The sensitivity control varies the "silence" zone through a predetermined range.
Many types of compasses have been proposed, but many of them require that the operator of the boat or other vehicle in which the compass is provided watch the compass to detect when the boat has deviated from the desired course. It would be desirable to have a relatively simple compass which would produce audible sounds that would indicate a deviation of a boat or other vehicle from a desired course without requiring the operator to watch the compass. Such a compass would be particularly useful on small boats where the crew, or sometimes a single sailor, is often too busy to watch a visual compass.
SUMMARY OF THE INVENTION
The present invention is an audio compass in which light sensed by devices such as photocells is controlled by polarized transparent sheets associated with a magnetic compass, and circuit means is responsive to changes in the electrical characteristics of the photocells to produce audible tones of different frequencies. A first tone of one frequency indicates a deviation of the compass or boat to one side of a desired heading, and a second tone of a different frequency indicates a deviation of the compass or boat to the other side of the desired heading. The tones are interrupted or modulated at a rate related to the magnitude of the deviation. Thus, by listening to the tone, an operator can tell when the boat deviates from the desired heading and the boat can be steered back onto that heading. In the preferred embodiment, no tone is produced when the boat is on the desired heading, although this condition could be indicated by still a third tone.
Accordingly, it is an object of the present invention to provide an audio compass which indicates left and right deviations from a desired heading of a boat by producing first and second tones of different frequencies corresponding to the left and right deviations.
Another object of the present invention is to generate the tones by controlling light received by photocells of the audio compass.
A further object of the invention is to accomplish the controlling of the light with polarized sheets through which the light shines.
Another object of the invention is to interrupt or modulate the tones at a rate which is related to the magnitude of the deviation of the compass or the vehicle from a desired heading.
Among the other objects of the invention are to provide an audio compass which is relatively simple and straightforward; which is reliable in operation; in which the parts cooperate efficiently and uniquely; and which can be produced economically on a practical manufacturing basis.
Other objects of this invention will appear from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly cut away, showing an audio compass in accordance with one embodiment of the invention;
FIG. 2 is a vertical sectional view taken along Line 2--2 of FIG. 1 and looking in the direction of the arrows;
FIG. 3 is a plan view similar to FIG. 1, but showing how a compass ring and two polarized sheets of the compass are rotated to set the audio compass at a desired heading;
FIG. 4 is a reduced plan view illustrating a deviation of the compass to the right of a desired heading;
FIG. 5 is a reduced plan view illustrating a deviation of the compass to the left of a desired heading; and
FIGS. 6, 7 and 8 show schematically successive portions of the electrical circuit in the present invention for producing an audible signal in response to a deviation of the compass from the desired heading.
Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.
DETAILED DESCRIPTION
The audio compass of the illustrated embodiment of the invention includes a magnetic compass 10 shown in FIGS. 1 through 5 and electronic circuit means shown in FIGS. 6 through 8. Referring first to FIGS. 1-5, the magnetic compass 10 has a housing 12, which in this embodiment is a bowl, and a transparent face plate 14 which covers and seals the top of the housing 12. The housing 12 and the face plate may contain a compass fluid on which certain components float as will be described. The face plate 14 may be threaded at 16 to screw into matching threads in the upper lip at the perimeter of the housing 12.
The magnetic compass 10 has a magnetic needle 18 for pointing north in accordance with conventional magnetic compass techniques. The needle 18 is mounted on and affixed to a polarized transparent sheet 20 which is pivoted on a stem 22 such that the sheet 20 and the needle 18 can swing freely about the stem 22. In this embodiment, the stem 22 extends upward from a dome 24, and the bottom of the dome is affixed to the housing 12. As indicated by the vertical lines 26 in FIG. 1, the plane of polarization of the transparent sheet 20 is permanently aligned with the longitudinal direction of the magnetic needle 18.
A compass ring 28 graduated in degrees is rotatably mounted on the circular lip 30 at the top of the housing 12 so that the ring 28 can be rotated through 360° and will stay at any selected position. In the illustrated embodiment, the ring 28 has a slot at 32 which receives the perimeter of a circular ring 34 which is fastened to the lip 30 as with screws 36.
Fixed to the ring 28 are two polarized transparent sheets 38 and 40 which are concentric with each other. Sheet 40 is a disc located at the center of ring 28, and sheet 38 is a ring surrounding and attached to disc 40. Ring-shaped sheet 38 is also attached to ring 28. The attachment of the sheets 38 and 40 to each other and to the ring 28 may be accomplished with adhesive material.
As indicated by the lines 42 and 44 in FIG. 1, the planes of polarization of the sheets 38 and 40 are offset from each other by an angle which is bisected by the polarization plane 26 of the sheet 20 when the zero degree mark of the compass ring 28 is set at north as in FIG. 1. In the illustrated embodiment, the polarization plane represented by the lines 42 for sheet 38 is offset 45° clockwise from the zero degree mark and the polarization plane represented by the lines 44 for sheet 40 is offset 45° counterclockwise from the zero degree mark. With the zero degree mark set at north,the two polarization planes 42 and 44 are bisected by the polarization plane 26 which is aligned with the north direction.
The sheet 20 floats on compass fluid contained in the housing 12. The housing 12 is ordinarily supported by gimbals of a gyroscope to keep it level.
A light source 46 is contained in the dome 24, and light from this source shines upward through the stem 22 and around the stem 22 which may be transparent. The rest of the dome 24 may be opaque. This light shines through sheet 20 and also shines through the central sheet 40. A photocell 48 is mounted on a bracket 50 which is attached to the housing 12 in a position to receive the light from the source 46. The amount of light received by the photocell 48 is related to the orientation of the sheets 40 and 20 as will be explained further.
Another light source 52 is mounted inside a dome 54 which has a transparent window 56. The rest of the dome is opaque. Light from the source 52 shines through the window 56 and through the sheet 20 as well as the outer ring-shaped sheet 38 which is affixed to the compass ring 28. Another photocell 58 is mounted on the bracket 50 in a position to receive the light from the source 52. The amount of light received by the photocell 58 is controlled by the orientation of the sheets 38 and 20 as will be explained further.
The magnetic compass 10 is ordinarily mounted in a boat or other vehicle. The compass is utilized to assist the operator, which may be the helmsman, to steer the boat on a desired heading. The heading is set in a manner illustrated in FIG. 3. In FIG. 3, the compass ring 28 has been rotated clockwise to a heading of 315°. After this heading has been set, the boat is turned counterclockwise to bring the zero degree mark back to the north heading which will place the compass in the condition illustrated in FIG. 1. Thus, as long as the zero degree mark is kept at the north heading, the boat will be on course. To assist the helmsman in accomplishing this, the circuit means illustrated in FIGS. 6-8 is provided. This circuitry is coupled to the photocells 48 and 58, and it produces first and second audio frequency tones of different frequencies which are interrupted or modulated at rates related to the intensity of the light received by the two photocells 48 and 58. A shift of the sheets 40 and 38 to the left or right from north position shown in FIG. 1 increases the light received by one of the photocells and decreases the light received by the other photocell. As will be explained, this produces a tone which is interrupted at a rate related to the magnitude of the change in light received by one of the photocells. In the illustrated embodiment, it is the photocell which receives an increased amount of light that produces a tone.
Referring to FIG. 6, the photocells 48 and 58 are visible at the left side of the drawing. Photocell 48 receives more light when the compass rotates to the right of the north heading as illustrated in FIG. 4 because the plane 44 tends to become more nearly aligned with the plane 26, so more light passes through sheets 40 and 20 to the photocell 48. Photocell 58 receives more light when the compass rotates to the left of a north heading as illustrated in FIG. 5 because the plane 42 becomes more nearly aligned with the plane 26 so that more light passes through sheets 38 and 20 onto photocell 58. Conversely, less light reaches photocell 58 when the compass rotates to the right, and less light reaches photocell 48 when the compass rotates to the left. It will be understood that this relationship could be reversed if desired.
The photocells 48 and 58 are connected to (or may be considered part of) two signal producing means 100 and 102. The signal producing means 100 includes a voltage divider 104 with resistors 106, 108 and 110 connected between supply terminals 112 and 114, together with amplifying transistors 116 and 118 and resistors 120 and 122. The signal producing means 100 produces a right error signal at output 124.
Signal producing means 102 includes a voltage divider 126 consisting of resistors 128, 130 and 132 connected between supply terminals 134 and 136, together with amplifying transistors 138 and 140 and resistors 142 and 144. A left error signal is produced at the output 146 of signal producing means 102.
The error signals appearing at outputs 124 and 146 are proportional to the change in the light received by the photocells 48 and 58 when the magnetic compass 10 deviates from the north setting shown in FIG. 1. The porportionality of these signals to the change in light is effective only through a certain range which is represented by the positive range R and the negative range -R illustrated in FIGS. 4 and 5. The illustrated range is arbitrary, and some other effective range could be utilized.
The signal output 124 is connected by line 148 to the input 150 of a variable frequency astable multivibrator circuit 152. Similarly, the signal output 146 is connected by line 154 to the input 156 of another variable frequency astable multivibrator circuit 158. The multivibrator circuit 152 is connected to a right channel oscillator circuit 160, and the multivibrator 158 is connected to a left channel oscillator circuit 162. Oscillator 160 may have a stable frequency of 1000 cycles per second, by way of example, and oscillator 162 may have a stable frequency of 400 cycles per second, by way of example. Oscillator 160 has an enabling transistor 164 which is connected through transistors 166 and 168 to a line 170 which leads back to a Schmidt trigger circuit, the input 174 of which is connected to the error signal output 124. Similarly, oscillator 162 has an enabling transistor 176 which is connected through transistors 178 and 180 to a line 182 which leads back to a Schmidt trigger circuit 184, the input 186 of which is connected to the error signal output 146. In operation, the error signal appearing at output 124 activates the Schmidt trigger circuit 172 which, in turn, feeds an enabling signal via line 170 to the enabling transistors 168, 166 and 164 to activate the oscillator 160. The oscillator 160 is operative only when the error signal appearing at output 124 increases in magnitude. On the other hand, when the error signal appearing at output 146 increases, Schmidt trigger circuit 154 is activated to feed an enabling signal via line 182 to the enabling transistors 180, 178 and 176 which turn on the oscillator 162. The oscillator 162 is operative only when the error signal appearing at output 146 increases in magnitude.
The right channel error signal, which is fed via line 148 to the multivibrator circuit 152, causes the flip-flop transistors 188 and 190 of the multivibrator to turn on alternately. Pulses produced by the flip-flop transistors 188 and 190 appear at line 192 and these pulses are fed to the enabling transistor 166. The pulses cause the operation of the oscillator circuit 160 to be interrupted or modulated at the repetition rate of the pulses. This pulse repetition rate is proportional to the magnitude of the right channel error voltage appearing at input 150 of the multivibrator circuit 152.
Multivibrator circuit 158 and tone oscillator 162 operate in the same manner. The left channel error signal appearing at input 156 causes flip-flop transistors 194 and 196 to turn on alternately. These transistors produce pulses at line 198 which are fed to the enabling transistor 178. The pulses cause the tone oscillator 162 to be interrupted at a rate which is proportional to the repetition rate of the pulses. The pulse repetition rate is proportional to the magnitude of the left channel error voltage fed to multivibrator circuit 158.
The modulated tone signals are delivered from the oscillators 160 and 162 at outputs 200 and 202. These tone signals are fed via a common line 204 to the audio output circuit 206 illustrated in FIG. 8. The audio output circuit includes an audio amplifier 208 which supplies the modulated tones through a transformer 210 to a transducer 212 which might be a loudspeaker or earphones by way of example.
The audio compass has a "silence" or "null" zone in which no signals are produced. This zone occupies a predetermined number of degrees left and right from the north heading. The "null" zone might occupy only plus or minus one degree, by way of example, but by adjusting the potentiometer 214, the "null" zone could be increased to say plus or minus five degrees. Assuming that the "null" zone is set at five degrees the right error signal would start producing modulated tones when the compass rotates five degrees to the right or clockwise as illustrated in FIG. 4, and the left error signal would start producing modulated 400 cycle tones when the compass has rotated five degrees to the left as illustrated in FIG. 5. The symbols E and -E in FIGS. 4 and 5 respectively, indicate the error or deviation from the desired heading. In FIG. 4, the error E and in FIG. 5 the error -E are right 5 degrees and left five degrees respectively. The error E would produce a 100 cycle tone interrupted at a rate proportional to the magnitude of the error, and the error -E would produce a 400 cycle tone interrupted at a rate proportional to the magnitude of the error.
Switches 215 and 216 are on-off switches. Potentiometer 218 provides a volume adjustment. Potentiometer 220 provides a zero adjustment. The light sources or lamps 46 and 52 are connected to the potentiometer 220.
It will be recognized that the individual circuits of the system are standard. The Schmidt trigger circuits 172 and 184 may be in the form integrated circuits 222 and 224 provided with amplifying transistors 226, 228, 230 and 232. The transistors 188, 190 may have input transistors 234 and 236, and the transistors 194 and 196 may have input transistors 238 and 240. Right channel tone oscillator 160 includes transistors 242 and 244 and left channel tone oscillator 162 includes transistors 246 and 248. The audio amplifier 208 in FIG. 8 may be an integrated circuit. The various biasing components of the circuitry are standard and will not be described in detail.
CONCLUSION
Thus, the invention provides an audio compass which is simple and reliable in operation. If the heading error increases, one photocell output increases and the other photocell output decreases.
The signal producing circuits receive the photocell outputs and cause one of the two Schmidt trigger circuits to fire. The increasing photocell output causes the corresponding oscillator to be enabled, and causes the appropriate astable multivibrator circuit to increase its pulse repetition rate according to the magnitude of the heading error. The multivibrator output gates the corresponding audio tone oscillator into the audio amplifier, which in turn, drives the output loudspeaker. The sensitivity control varies the "silence" zone through a predetermined range.