Automatic tuning system

An automatic tuning system for controlling the avionics in an aircraft includes an operator actuated keyboard for entering any available frequency for the many avionic receiver/transmitters and/or transponders employed in the aircraft. Signals from the keyboard are applied to a microprocessor programmed to detect first a valid frequency selection for one of the instruments aboard the aircraft and provide control output signals which are converted to a data format for tuning the device to which the selected frequency applies to the frequency selected. Such a system eliminates the need for the pilot or other operator to individually tune a particular device since it is necessary only to enter a desired frequency with a control signal being automatically applied to tune the electronic unit to which the selected frequency corresponds.

BACKGROUND OF THE INVENTION 
The present invention relates to a control system for controlling the 
frequency of operation of aircraft radio communication and navigational 
apparatus. 
Modern aircraft are equipped with a multitude of navigational and 
communication transmitters, receivers and transponders, all of which must 
be tuned to specific frequencies in specific areas of travel for 
operation. In the past, each electronic unit included its own frequency 
controlling means such as dials, switches, or the like which the operator 
of the aircraft had to individually control. Improvements over such manual 
tuning systems have been made where, for example, as disclosed in U.S. 
Pat. No. 3,701,945 issued Oct. 31, 1972, a system is provided in which a 
keyboard is provided for entering the desired frequency into the control 
system for each of the various avionics involved. This system, however, 
requires not only the frequency selection but also that the operator 
select the instrument being tuned by the frequency entered. Other prior 
art patents disclose a variety of methods of tuning avionic receivers or 
transmitters using digital controls and/or for storing information 
pertaining to selected frequencies. Representative of such prior art are 
U.S. Pat. Nos. 4,075,567; 4,119,915; and 4,122,395. 
SUMMARY OF THE PRESENT INVENTION 
The system of the present invention provides a single step tuning control 
system and method by which the operator enters a frequency for any of the 
many receiver/transmitters of the aircraft and signals representative of 
such frequency are correlated with stored data identifying all available 
frequencies and if a valid frequency has been selected, a control output 
signal is provided to automatically tune the device to which the selected 
frequency pertains. Systems embodying the present invention include a data 
entry means such as a keyboard coupled to a microprocessor programmed to 
test the entered frequency against all available frequencies for devices 
in the aircraft and provide control output signals if a valid frequency 
has been entered by the operator. The control output signals are employed 
for the automatic tuning of a device to the selected frequency. An illegal 
entry display is provided to alert the operator in the event an erroneous 
frequency is entered. 
Thus, the system of the present invention provides a single step tuning 
process for the many avionic receiver/transmitters of an aircraft thereby 
simplifying the tuning process for the aircraft operator. Further, the 
system prevents mistuning of any of the avionics. These and other 
features, advantages and objects of the present invention can best be 
understood by reference to the following description thereof together with 
the accompanying drawings in which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1 there is shown an electrical control system 
for use in practicing the preferred embodiment of the invention. The 
system includes a conventional digital keyboard and interface circuit 10, 
the latter of which may comprise, for example, a commercially available 
National Semiconductor encoder type 54C922 which is coupled to interface 
with a microprocessor 12 such as an Intel 8080. The microprocessor is 
intercoupled with a ROM memory 14 such as commercially available 2716 or 
2708 integrated circuit chips which are programmed with the control 
program. Temporary storage for data is provided in a RAM memory 16 also 
coupled to the microprocessor. RAM memory 16 may comprise, for example, 
commercially available 2102 integrated circuit chips. 
Output signals from microprocessor 12 are applied to a UART 18 such as a 
National MM5305 for converting the parallel data therefrom into a serial 
format. Serial data from UART 18 is transmitted to a pair of additional 
UARTS 20 and 22 which convert the serial data to parallel 8 bit output 
words applied to data format convertor units 24, 26 and 28 associated with 
UART 20 and to a display 30 associated with UART 22. The parallel data 
from UART 22 is applied to a decoder 23 for converting the data into a 
suitable display data format which signals are then applied to display 
drivers 25 and subsequently to a display unit 30 and an entry display 38 
(through interconnection A) positioned physically adjacent keyboard 10 
permitting the operator to monitor the entry of numerical data 
corresponding to a selected frequency. The display unit 30 comprises an 
array of individual digital displays corresponding to the particular 
avionics used by the aircraft. Thus, for example, display 31 can be a six 
digit high intensity filament-type digital display (as are the remaining 
displays) for the communication frequency which falls within the frequency 
range of 118 to 135.975 MHz tunable in 25 KHz increments. Display 32, for 
the navigational frequencies such as LOC/VOR, can be a five digit display 
covering the navigational frequency band of 108 to 117.95 MHz. Display 33 
comprises a four digit display for the ADF, tunable within a range of 200 
to 1799 KHz. Display 34 is a six digit display for the high frequency 
band, tunable between 2 to 29.9999 MHz, tunable in 100 Hz increments. 
Display 35 can be a two digit display for displaying the DME channel 
associated with the navigational frequency selected as described in 
greater detail below. Finally, display 36 for the transponder comprises a 
four digit display for displaying the transponder code. 
The data format converting circuits 24, 26 and 28 comprise commercially 
available circuit elements such as integrated circuit chips 74S288 or 
other standard T.sup.2 L or CMOS logic circuits for converting the 
parallel 8 bit words from UART 20 to a BCD code, a two out of five code, 
or to serial data through a UART 29 for circuits 24, 26 and 28 
respectively to provide a control command signal having a format suitable 
for automatically controlled avionic receivers/transmitters. The BCD code, 
two out of five code, and serial data from UART 29 are the standard data 
formats employed by commercially available avionic devices such as 
communication receivers, transponders, ADF receiver/transmitters and the 
like manufactured by Collins Radio, King, or RCA Corporation. These 
receiver/transmitters are specifically designed to accept the particular 
data format and respond thereto to tune the device to the selected 
frequency defined by the control command input. In FIG. 1 only three such 
data converting circuits are shown, it being understood that depending on 
the number of tuned devices being controlled, a greater or fewer number 
can be provided. 
Naturally, keyboard 10 is located at a convenient position in the cockpit 
of the airplane as are displays 30 and 38 such that the pilot can select a 
desired frequency and monitor the display 30 as desired. In the event a 
frequency is entered which does not correspond to one of the permitted 
frequencies, display 38 will flash indicating that a frequency entered by 
the pilot is not a permitted frequency for any of the 
receivers/transmitters. Alternatively, other alarm means, either visual or 
acoustical can be provided to indicate to the pilot that a nonpermitted 
frequency has been entered at the keyboard. Having described the hardware 
comprising the system of the present invention, a description of the ROM 
programming for microprocessor 12 to achieve the comparison of the entered 
frequency signals from keyboard 10 with stored data testing for permitted 
frequencies and for generating the desired command control signals for 
tuning the aircraft receiver/transmitters is now presented in conjunction 
with FIGS. 2-8. 
Referring initially to FIG. 2 which shows the basic program flow diagram, 
the microprocessor after initialization is awaiting a new entry as 
indicated by the encircled W entry point. A desired frequency for one of 
the avionic systems is entered by the pilot using keyboard 10 by entering 
the sequential numbers for the frequency and a decimal point either at the 
end or where it might otherwise occur in the frequency (except for the 
transponder) and activating an enter key as indicated by block 40 in FIG. 
2. The first decisional block 42 tests the entered number to ascertain if 
it includes a decimal point. All frequencies with the exception of the 
transponder which includes numbers 0000-7777 are entered using a decimal 
point either within the frequency or at the end thereof. Thus, if no 
decimal point is detected, the program goes to the transponder routine as 
indicated by entry point T. FIG. 3 shows the details of the transponder 
routine. In the transponder subroutine, the microprocessor programs and 
checks the entered number to see if it is less than 0 as indicated by 
block 44. If it is a negative number, then a mistake has been made and the 
program goes to the illegal entry routine indicated as block 46 in FIG. 4. 
The illegal entry point I enunciates the illegal entry as indicated by 
block 46 which causes the entry display 38 to flash thereby indicating to 
the operator that a numerical entry has been made which does not 
correspond to any of the frequencies available on the 
receiver/transmitters of the aircraft. Once the illegal entry has been 
annunciated, the program returns to the awaiting new entry. 
If the entry without a decimal is greater or equal to 0, the transponder 
routine shown in FIG. 3 is continued by decisional block 48 in which the 
number is tested against the number 7777 to ascertain if the number 
entered is, in fact, a transponder code. If the number is greater than 
7777, again the program returns to the illegal entry routine shown in FIG. 
4. If not, the program proceeds to decisional block 50 to test to see if 
it is a valid octal number for the transponder. If not, the program 
proceeds to the illegal entry routine but if a valid octal number, it 
continues to the transponder tuning block 52 corresponding to the 
generation of a command control signal for tuning the transponder 
receiver/transmitter while simultaneously providing a signal to the 
display 36 to cause the display of the entered number. Thus, the 
microprocessor provides output control signals applied to UARTS 18, 20 and 
22 to the respective logic circuits for providing a control signal to the 
transponder for automatically tuning to the set code and for providing a 
display of the transponder code by display 36. 
Once this is done the program returns to the awaiting new entry point and 
assuming that a different transponder code is not selected, but that the 
pilot enters a frequency for the HF receiver/transmitter, the next 
decisional block 54 in FIG. 2 is a test to see if the entered number is 
less than 2.0. 
If the entered number is less than 2.0, there is no frequency band 
corresponding to this number and as before, the program proceeds to the 
illegal entry routine. If it is greater than 2.0 as indicated by the next 
test, decisional block 56 is to ascertain whether or not the number 
entered is less than or equal to 29.9999. The tests indicated by blocks 54 
and 56 thereby determine whether or not the frequency entered falls within 
the high frequency band of 2 to 29.9999 MHz. If it does, the program 
proceeds from block 56 to the high frequency routine shown in FIG. 5. 
Since the frequencies available for the high frequency band are in 100 Hz 
increments, a test indicated by decisional block 58 is conducted on the 
entry to ascertain whether it is evenly divisible by 0.0001. If it is not, 
it indicates that the entered number is an illegal entry and the program 
proceeds to the illegal entry routine of FIG. 4. If, however, the entered 
frequency lies between 2 and 29.9999 and is evenly divisible by 0.0001, it 
indicates that a valid high frequency has been entered by the pilot and 
the resultant control signal is generated as indicated by block 60 to tune 
the high frequency receiver/transmitter and provide a signal annunciating 
the selected frequency on the high frequency display 34 shown in FIG. 1. 
After this is completed, the program recycles to the awaiting new entry 
block and assuming that neither a transponder or high frequency is next 
selected by the operator, the program cycles to the next decisional block 
62 which tests to see if the entered number is less than 108.00. 
If the entered number is less than 108.00 and greater than 29.9999, it is 
not a valid frequency for any of the avionics on the aircraft. Thus, if it 
falls within this number range the program proceeds to the illegal entry 
routine. If, however, it is greater than 108.00 then it proceeds to the 
next decisional block 64 in which the entered number is compared with 
stored data to ascertain whether or not the frequency is less than or 
equal to 117.95. Thus, the effect of blocks 62 and 64 is to ascertain the 
existence of a selected LOC/VOR frequency lying within the frequency band 
of 108 to 117.95 MHz. If the number entered falls within this frequency 
bank, the program proceeds to the navigational routine indicated by the N 
and shown in detail in FIG. 6. 
In the navigation routine the first decision block 66 tests the entry first 
to ascertain whether or not its evenly divisible by 0.05. Each of the 
navigational frequencies will, in fact, be so divisible and if not, the 
program actuates the illegal entry routine annunciator shown in FIG. 4. If 
the entry is divisible by 0.05, then it is further tested to find out if 
it is evenly divisible by 0.1 as indicated by decisional block 68 in FIG. 
6. This further test is to ascertain whether or not one of the DME 
frequencies has been selected. If not, the DME receiver is turned off as 
indicated by block 70 in FIG. 6 and the program proceeds to block 76. 
If a navigational frequency has been selected in which a DME signal is 
transmitted, it will be evenly divisible by 0.1 and the program proceeds 
to block 72 in which the DME channel number corresponding to the entered 
frequency is obtained from the channel number correlation stored in the 
ROM memory 14 (FIG. 1). Further, as indicated by block 74, the DME is 
tuned to the desired channel and the channel number annunciated by DME 
display 35 after which a test is run to ascertain whether or not the 
frequency entered is less than or equal to 111.95 as indicated by 
decisional block 76. This test is run to ascertain whether or not an ILS 
frequency has been selected and if it has not, the localizer and glide 
slope receivers are turned off as indicated by block 78 while the VOR is 
tuned to the entered frequency (block 80) and annunciated by display 32 
(FIG. 1) and the system returns to await a new entry. 
If, however, a navigational frequency is selected in which a localizer and 
glide slope frequency exists, the decision in block 76 is that a frequency 
is less than or equal to 111.95 and the test indicated by block 82 is run 
to ascertain whether the entered frequency has a tenth's digit which is 
odd. If not, the function of blocks 78 and 80 are run. If the test of 
block 82 is positive indicating that the frequency corresponds to one with 
a localizer and glide slope transmission, as indicated by block 83, the 
VOR receiver is tuned to an off status since a VOR frequency has not been 
entered but a localizer frequency has been entered by the pilot. The 
localizer frequency is then entered and annunciated as indicated by block 
84 while the corresponding glide slope frequency is determined as 
indicated by block 86, the glide slope receiver is tuned and the frequency 
annunciated as indicated by block 88 after which the program returns to 
await the new entry. 
If a navigational frequency has not been entered and the proceeding tests 
54, 56, 62 and 64 of the flow chart of FIG. 2 have all been negative, the 
program proceeds to decisional block 90 where the entered number is 
compared with a stored reference number to see if it is less than 118.000. 
If it is, the program proceeds to the illegal entry routine and if not, a 
further check is made as indicated by decisional block 92 to ascertain if 
the frequency entered is less than or equal to 135.975 MHZz. The test to 
this point thus ascertains whether or not a communication frequency within 
the band of 118 to 135.975 MHz has been entered. If it has, the program 
proceeds to the communications routine indicated by the encircled C which 
is shown in detail in FIG. 7. 
In the communication routine the entered information is checked to see if 
it is evenly divisible by 0.025 as indicated by decisional block 94. Since 
the communication frequencies are all increments of 25 KHz, if a 
communication frequency has been entered, it will be evenly divisible by 
0.025 and the communication receiver will be tuned as indicated by block 
96 and annunciated by display 31 (FIG. 1) with the program then returning 
to await a new entry. If, however, the number is not evenly divisible by 
0.025, a further test is conducted as indicated by block 98 to ascertain 
if the hundredths digit is 2. The function of the further test is to 
permit the pilot to enter as part of a valid communication frequency only 
the tenths or hundredths least significant digits to achieve the correct 
frequency. Thus, the decisional block 98 checks to see if the hundredths 
digit is a 2 and if it is, it checks the thousandths digit to ascertain if 
it is a 0. If it is a 0, and all the remaining less significant digits are 
0, the system automatically adds 0.005 to the entered frequency as 
indicated by block 102 and the communication receiver/transmitter is tuned 
to the resultant frequency as indicated by block 96. 
If the pilot entered hundredths digit is not a 2, a check is made to see if 
the hundredths digit is a seven and if it is, again the test indicated by 
block 100 is conducted to ascertain if the thousandths digits and those to 
the right are zeroes. If so, 0.005 is again added to the entered frequency 
and the resultant frequency entered to the tuning block 96. If, as 
indicated by block 104, the hundredths digit is not a seven, then an 
illegal entry has been made and the program annunciates an illegal entry 
by flashing the enter display 38 (FIG. 1) as shown by the subroutine of 
FIG. 4. 
If none of the above tests have been met, the system next checks to see if 
the entry is less than 200.0 as indicated by block 106. If it is, then 
there are no frequencies remaining corresponding to a valid entry and the 
system goes to the illegal entry routine. If the entered frequency is 
greater than 200, a further test is made as indicated by decisional block 
108 to ascertain whether or not the entered frequency is less than or 
equal to 1799.0 which provides a check to see if the frequency falls 
within the 200 to 1799.0 KHz frequency band corresponding to the ADF 
frequency allocation. If it is, the program proceeds to the ADF routine 
shown in FIG. 8 where the entered number is checked as indicated by 
decisional block 110 to see if it is evenly divisible by 1. If not, the 
program proceeds to the illegal entry routine. If it is, however, the 
frequency entered corresponds to a valid ADF frequency and the ADF 
receiver is tuned and the frequency annunciated by display 33 (FIG. 1) as 
indicated by block 112. After the ADF receiver is tuned and the frequency 
annunciated, the system returns to await a new keyboard entry. 
Thus, the system of the present invention provides a series of digital 
tests on the data corresponding to the entered frequency to ascertain 
which assigned band the entered frequency corresponds to. If the frequency 
falls within a given band but is not a valid frequency within the 
bandwidth, or does not fall within an assigned frequency band, an alarm to 
the pilot indicates that an improper frequency has been selected and no 
control signal is generated to tune the receivers/transmitters. This 
prevents mistuning of any of the avionics of the aircraft. Further, the 
system automatically scans through the available frequencies to ascertain 
which of the avionic units are to be tuned and provides control signals 
for automatically tuning the same together with display signals indicating 
to the pilot that the unit has been tuned to such frequency. 
It will become apparent to those skilled in the art that the particular 
tests conducted and the arrangement of such tests in the system of the 
preferred embodiment can be varied. If the avionic frequency bands or 
individual frequencies within such bands are changed by F.C.C. 
regulations, naturally the test comparisons can be modified to verify the 
entry of a valid frequency. These and other modifications can be made by 
those skilled in the art without departing from the spirit or scope of the 
present invention as defined by the appended claims.