NARROW BAND SCANNING RF RECEIVER

Abstract: The narrow band scanning RF receiver (12) includes a ph ase-locked loop radio frequency stage having a reference oscillator (38) for receiving a radio frequency signal. The radio frequency stage has a frequency which may be selected by a controller via a selectable frequency signal supplied to the reference oscillator (38). The controller tests for the presence of a legitimate radio frequency signal and also temporarily inhibits the tuned radio frequency stage when changing from a first selected frequency to a second selected frequency. The receiver (12) produces an output for controlling an electric motor (100) for operating a barrier.

Description: NARROW BAND SCANNING RF RECEIVER CROSS REFERENCE TO RELATED APPLICATION Priority is claimed from U.S. provisional application no. 60/146,620, filed July 30, 1999. FIELD OF THE INVENTION The invention relates in general to radio frequency receivers and in particular to a narrow band scanning radio frequency receiver for use in a barrier operator such as for controlling a garage door, a gate or the like. BACKGROUND OF THE INVENTION Barrier operators including garage door operators, commercial door operators and gate operators typically include a radio frequency receiver for receiving a radio frequency carrier transmission modulated with a code. The radio frequency receiver demodulates the code and supplies it to a microcontroller or the like. The microcontroller determines whether the code is an authorized code. Upon concluding the code is authorized the microcontroller commands other portions of the circuit including relays and like to provide electrical energy to a motor causing a door to be opened or closed or a gate to be opened or closed. One of the problems associated with such systems is that under regulations from the Federal Communications Commission the transmitters may only be licensed for relatively low amounts of output power. As a result the range at which a code transmission may be received is relatively short and may typically vary from about a foot to about one thousand feet. Many transmitters used for garage door operation operate at about 390 MHz for their carrier frequency. Other transmitters may also be operating at the same frequency such as amateur radio transmitters. Parasitic transmitters such as computers which may be emitting electromagnetic interference at 390 MHz. As a result it may be relatively difficult for a receiver to determine when it is receiving a code transmission and when it is receiving noise. If the receiver cannot separate a code signal from the noise it will not command the operation of the barrier. In addition, transmitters such as those used for commercial door operators and the like must of necessity be kept inexpensive. As a result, analog signal circuitry is typically used in the RF stages of the transmitter and may have manufacturing tolerances which cause multiple transmitters to emit slightly different carrier frequencies. As a result, there may be transmitters at 388 MHz, 389.5 MHz, 390.4 MHz and the like. The bandwidth of the modulated signal, however, is relatively narrow. As a result, in the past what is usually done is to use a relatively wide band receiver which was capable of receiving signals from transmitters having slightly varying carrying frequencies. The result of using such a wide band receiver would be an increase in the amount of noise which the receiver is processing and hence a decrease in the likelihood that faint signals from relatively distant transmitters could be received and properly acted upon. What is needed then is a system for improving the signal to noise ratio of a receiver in order to select legitimate coded transmission from distant transmitters from a noisy background. SUMMARY OF THE INVENTION A movable barrier operator for opening and closing a movable barrier in response to a coded radio frequency signal has a tuned radio frequency stage for receiving a radio frequency signal. The tuned radio frequency stage having a resonant frequency which may be selected by a controller. The controller selects a plurality of resonant frequencies of the tuned radio s ' tage and detects whether the output of the tuned radio frequency stage is a legitimate radio frequency signal. The controller also produces a temporary RF stage inhibit signal when changing from a first selected radio frequency to a second selected radio frequency. A electric motor control circuit responds to the controller to control an electric motor connected to a barrier such as a door or a gate to move the barrier. It is a principal aspect of the present invention to provide a radio frequency receiver which can rapidly scan over a plurality of channels to detect off-center frequency transmissions from low cost code transmitters and control a barrier in response thereto. Other aspects of the present invention will become obvious to one of ordinary skill in the art upon a perusal of the specification and claims in light of the accompanying drawings . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of narrow band scanning radio frequency receiver of a movable barrier operator embodying the present invention; FIG. 2 is a block diagram of a portion of the motor control circuitry of the movable barrier operator shown in FIG. 1; FIG. 3 is a schematic diagram of the narrow band scanning radio frequency receiver of the apparatus shown in FIGS. 1 and 2 ; FIGS. 4-7 are flow diagrams showing the operation of a microcontroller within the radio frequency receiver; and FIG. 8 is a timing diagram of a received pulse train.. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The scanning receiver 12 includes a radio frequency antenna 14 for receipt of coded radio frequency transmissions which are then fed to a wide-band passive filter 16 which has a bandwidth of plus or minus 3 MHz around 390 MHz center frequency. The signal is then fed to an integrated circuit 18 comprising a superheterodyne receiver which in this case is comprises of a Mitel KEΞRX04 integrated circuit. The signal is fed to a jurr- 1 ion point in the circuit 20 which is then fed to an intermediate frequency filter 22 center tuned at 10.7 MHz having a bandwidth of 470 KHz. Through the action of a local oscillator 24, which will be described hereinafter, a 10.7 MHz down-converted signal is then fed to an audio- out system 26 which provides data to a Zilog Z86E08 microcontroller 28. In turn, the microcontroller has its scan mode and frequency step length characteristics set by a DIP switch 30 and controls a programmable clock generator 32 for generating a programmable signal fed on a line 34 to a crystal input terminal 36 of the integrated circuit 18. That variable frequency signal is then fed to a reference oscillator 38 which feeds a selected frequency signal to a phase detector 40. The phase detector 40 receives a divide by 64 input 42, based upon the local oscillator frequency, and provides at an output 44 a signal to a voltage controlled oscillator 46. Data is then fed out through a data outport 50 to other portions of the movable barrier operator or operator 10. The data out is then fed to a barrier control system 60 through a line 62 which is connected to an eight-bit microcontroller 64 of the type that might be sold by Zilog. The microcontroller 60 also receives inputs from a plurality of rotary switches 66 and a plurality of push button switches 68. The data received at the microcontroller 64 can be used a control a motor control system 100 of the system 10 which can be used to open or close a garage door operator, open or close a gate, or open or close a rolling door, or the like, by control of an electric motor 98. In order to determine whether an authorized user has sent the signal which is received from the DATA OUT pin, an external memory 70 includes a program memory and a data memory containing the user I.D. which is coupled to transfer information back and forth to the microcontr'- η ler 64. The microcontroller 64 is driven by a realtime clock 72 and provides an output 74 at a liquid crystal display. Audible outputs are also provided to a buzzer 76 and a motor control output is provided at a relay output 78 to the motor control system 100. Referring now to FIG. 4, in order to control the microcontroller 28 presented at a step 300 and the control scan bit is set in a step 302 a mode routine is called in a step 304 to test the DIP switches to determine whether the system is in a sweep mode in a step 306. If it is not in a step 308 the reference generator is programmed to generate 6.2608 MHz for a detected frequency of 390 MHz and the TO and Tl counts are stopped following which control is transferred to a step 310 testing whether it is the first frequency or the eighth channel. In the event that the sweep mode is set, control is transferred directly to step 310 which sets the frequency and a test is made in a step 312 determining whether the mode is set authorizing to scan. If it is not control is transferred back to the step 310. If it is control is transferred to a step 314 where the reference frequency is changed to 6.24 MHz and the second frequency is detected in a step 316. A test is made in a step 318 to determine whether the system is in mode two. If it is, indicating the frequency steps are 200 kHz, control is transferred to a step 320. If it is not a test is made to determine whether the system is in mode one in step 322. If it is not control is transferred to the third channel, which is 400 kHz from the first channel, at a step 324. If it is control is transferred to the step 320. A test is made in a step 322 to determine whether scans should continue and the frequency reference is changed in a step 328 to 6.2419 MHz the third frequency of the step 324. Another scan test is made in the step 330 and i it is OK to scan the third frequency is programmed in a step 332. The fourth frequency is started in a step 334. A mode two test is done in a step 336. A mode one test is done in a step 338. If the mode is either in mode one or mode two the fourth frequency is programmed in a step 340 and the test is made in a step 342 to determine whether scan is authorized. If it is the fourth frequency is finally programmed in a step 344. If it is not control is transferred back to the step 340. Similarly once the system has been programmed in a step 344 control is transferred to a step 346 for the fifth channel setup as were done for previous channels. Although not shown in the flow chart up to 31 channels can be stepped through and 200 kHz increments to cover a 6 MHz bandwidth around 390 MHZ center frequency. The use of the change in the reference frequency to reference generator allows the narrow band tuning to be done precisely and accurately over a wideband range. Referring now to FIG. 5, a pulse checking routine is entered in a step 360. A downwardly changing pulse edge is tested for in a step 632 and the counters are stopped in a step 364. Control bit is set in a step 366 and an initial value is step in a set 368 to begin running the code timer following which the routine is exited in a step 370. Referring now to FIGS. 6A through 6C, a positive edge is tested for in a step 400 and if it is found an output is turned on in a step 402. If the relay output is switched on for controlling the motor in a step 404 and valid code is not received a test is made to determine whether this is the first rising edge in a step 406. In the event that the first rising edge has been detected an exit routine step is executed in a step 408. If not the most significant bit of the timing bit is tested to see whether it is equal to two and control is transferred to a step 420, as shown in FIG. 6B indicating the period is between 0 and 35 milliseconds. From step 404 if the relay output code and valid code is received control is transferred to a step 422 indicating the relay as on. The code timer is decremented by one in a step 424. A test is made to determine whether the code timer is timed out in a step 426. If it is not the routine is exited in a step 428. If it has the relay output is set to be not on in a step 430. In the event that the result of step 407 is in the negative a test is made to determine whether the most significant bit Tl is equal to one. If it is the period is indicated to be between 35 and 70 milliseconds in a step 430. If it is not the period is indicated to be greater than 70 milliseconds in a step 432 and scanning continues in a step 434 indicating that valid code has not been received. If the period is set between 35 and 70 milliseconds a further test is made in a step 440 to determine whether Tl is greater than 110 or less than 55 milliseconds. If it is a bad pulse indication is flagged in a step 442. If as is shown in FIG. 6B the period is between 0 and 35 milliseconds a test is made in a step 450 to determine whether Tl is less than 1.78 milliseconds. If it is a bad pulse detect is flagged in a step 452. If it is not a test is made to determine whether it is between 5.2 and 25 milliseconds in a step 454. If it is control is transferred back to a lot condition step 460. If not control is transferred to a test step to determine whether T is between 25 and 35 milliseconds in a step 464. If it is control is transferred to the lock condition step. It is not for bad pulse as indicated in step 452. In the event that the second edge detected is a bad pulse in step 454 a counter is incremented in a step 460. In the event that the Tl p 2 se is between 110 and 55 milliseconds control is also transferred to the step 470. In the event that the lock condition 460 is set control is transferred to a step 480 wherein the control bits are set and a counter is tested to determine whether it is greater than or equal to a preset maximum value in a step 482. If it is the counter is forced to the maximum value in a step 484. If it is not it is incremented bytewise in step 486. After that control is transferred to step 470 following step 470. If a second edge is being detected it is indicated in a step 488 following which the timers are reset in a step 490 and the routine is exited in a step 492. The purpose of the entire routine set forth in FIGS. 6A, 6B, and 6C is to determine whether valid pulses are being received. If they are not scanning continues. If they are the pulse is indicated to be valid data and is then transferred to a suitable store in the microcontroller for further processing as data. A timing detector is also present as shown in FIG. 7. The timeout routine is started in a step 600. The number of pulses is decremented in a step 602 and a 0 test is made in a step 604. If the timer has timed out to 0 and indication is made in a step 606 that 500 1 milliseconds has elapsed from the last positive going edge received by the radio frequency system scanning is resumed in a step 608 and interrupts are masked out except for the IRQ interrupt following which the routine is exited in a step 610. In the event that the count is not 0 the countdown is restarted in a step 612 following which the routine is exited in a step 610. Thus, the routine set forth in FIG. 7 is for the purpose of determining whether the pulse sequence at that particular frequency has gone silent. If it has the phase lock loop is commanded to begin scanning in either 200 kHz or 400 kHz increments. Thus, the receiver's front end 16 will allow most of any RF noise or signal through. The intermediate frequency filter 22 of the integrated circuit 18 will perform the bulk of the noise filtering because of its narrow bandwidth (470 kHz) . The data output at data out 26 is processed by the microcontroller 28 for detection of the desired code. The microcontroller 28 will program the clock generator 32 serially accordingly. The output of the clock generator 32 is controlled by the microcontroller 28 so that it will increment or decrement by 200 kHz or 400 kHz in response to the DIP switch 30 settings when there is no valid code received. If a valid code is received then the microcontroller 28 will lock the clock generator output frequency thereby halting frequency sweeping of the local oscillator 24. When valid code is no longer present the microcontroller 28 will command the clock generator 32 to increment, resuming frequency sweeping. The input frequency will be swept back and forth across the desired range set by the DIP switches 30. Attached is an appendix comprising pages A-l threough A-20 which provides a listing of the software which executes on the microcontroller 28. While there has been illustrated and described a particular embodiment of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

Claims: WHAT IS CLAIMED IS: 1. A barrier operator for opening and closing a movable barrier in response to a coded radio frequency signal comprising: a phase-locked loop radio frequency stage for receiving a radio frequency signal, the phase-locked radio frequency stage having a reference oscillator and a reference oscillator input and having a selectable frequency which may be selected by selecting . a frequency of the reference oscillator; a controller for selecting a plurality of frequencies of the radio frequency stage and detecting whether the output of the radio frequency stage is a legitimate radio frequency signal, the controller causing a selected frequency signal to be supplied to the reference oscillator for controlling the frequency of the reference oscillator, the controller receiving an output from the radio frequency stage representative of the radio frequency signal; and an electric motor responsive to an output of a controller for opening or closing a barrier. 2. A barrier operator for opening and closing a movable barrier in response to a coded radio frequen-:; signal according to claim 1 wherein the controller inhibits the radio frequency stage output when the controller changes the selected frequency signal supplied to the reference oscillator.

Inventors: CRIMMINS TERENCE, NGUYEN MICKEY, CRIMMINS, TERENCE, NGUYEN, MICKEY
Applicants: CHAMBERLAIN GROUP INC, CRIMMINS TERENCE, NGUYEN MICKEY, CRIMMINS, TERENCE, NGUYEN, MICKEY, THE CHAMBERLAIN GROUP, INC.
Application year: 2000
Main classification: G05B19
IPC codes: H03J7