RADIO FREQUENCY TRANSMITTER HAVING SWITCHED MODE POWER SUPPLY

Abstract: A hand-held radio frequency transmitter (10) for use in generating a coded radio frequency transmission has a switched mode power supply (12) energizable by a battery (52). A radio frequency oscillator (14) is driven by the switched mode supply. A modulator (146) controls operation of the oscillator which produces a coded radio frequency signal.

Description: RADIO FREQUENCY TRANSMITTER HAVING SWITCHED MODE POWER SUPPLY BACKGROUND OF THE INVENTION The invention relates in general to radio frequency transmitters and, in particular, to a switched mode power supply for a radio frequency transmitter. Garage door operators commonly may be controlled from wired switches as well as radio frequency transmitting switches such as hand-held radio transmitters. Hand-held radio transmitters are energized by a battery and it is desirable to maintain as long a battery life as possible. However, it is also important for hand-held radio trans¬ mitters to be inexpensive, while still conforming with requirements of the Federal Communications Commission for center frequencies, bandwidth limitations, power limi¬ tations and the like. In the past hand-held radio trans¬ mitters, particularly of the type disclosed in U.S. Patent No. 4,806,930 to Wojciak, Jr., were directed to battery operated systems wherein a radio transmitter might include a code generator as well as an oscillator having an output modulated in some fashion by a code generator for producing a modulated radio frequency output. The transmitter was energized by a battery E. Such a transmitter, however, was relatively bulky, in part because relatively large batteries, such as 9-volt and 12-volt batteries were used to energize the transmit ers. Today, however, people have come to enjoy keyfob-type transmitters which have very small volumes and, accordingly, in many cases are now using 3-volt lithium batteries. Unfortunately, 3-volt lithium batteries do suffer from voltage drop off with battery life and the initial voltage of the batteries as received from the supplier varies to some extent. As a result, the trans ¬ mitter radio frequency generating section will not always receive the same energizing voltage and this may lead to the transmitter drifting in frequency and possibly having its electrical characteristics effected greatly by the change in the battery voltage that it will be unable to oscillate at all and, hence, will be unable to generate a radio frequency signal. What is needed, then, is a hand-held radio frequency transmitter including a voltage stabilized power supply which is compact and has a relatively small number of components. SUMMARY OF THE INVENTION A hand-held radio frequency transmitter includes a switch mode power supply for delivering a pre-selected potential to a radio-frequency oscillator. The switched mode supply is controlled by a microprocessor or other digital logic device, such as an application-specific inte- grated circuit or a custom integrated circuit and includes a switch controlled by the microprocessor, which switch enables or disables current from flowing through an induc¬ tor coupled to a storage capacitor. A feedback loop is coupled to the storage capacitor for signalling the icro- controller when the storage capacitor has reached a pre¬ selected voltage. A radio frequency oscillator is connected to be energized from the storage capacitor and includes an input for receiving a modulating code. The modulating code causes the oscillator to be switched on and off, thereby producing a pulsed carrier wave which may be supplied to a garage door operator or other device to be operated. It is a principal aspect of the present invention to provide a hand-held radio frequency transmitter including a switch mode power supply driven from a battery for supplying uniform potential electrical energy to a radio frequency oscillator. Other advantages of the present invention will become apparent to one of ordinary skill in the art, upon - 3 - a perusal of the following specification and claims in light of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a hand-held radio frequency transmitter embodying the present inven¬ tion; and FIG. 2 is a flow chart showing operation of a microcontroller of the radio frequency transmitter shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now the drawings and especially to FIG. 1, a hand-held radio frequency transmitter embodying the present invention is generally shown therein and is iden¬ tified by numeral 10. The transmitter 10 includes a switch mode power supply 12 coupled to a radio frequency oscilla¬ tor 14. A microcontroller 16 produces a modulating code on an output line 18 which is supplied to the oscillator 14 for causing the oscillator 14 to generate radio frequency energy which is emitted by an antenna 20 and which may be received by a garage door operator or other device to be operated. A plurality of switches, respectively numbered 30, 32 and 34, are connected in parallel to a ground 36 and to three inputs 40, 42 and 44 of the microcontroller 16. Closure of switches 30, 32 or 34 each will respectively cause a different modulation code stream to be produced by the microcontroller 16 on the line 18. For instance, each of the switches may be dedicated to a particular garage door so that three garage doors could be operated separate- ly from the three switches. In the alternative, one of the switches might be dedicated to sending the code, which would cause a light to be illuminated within the garage even when a garage door is not being operated. In response to closure of one of the three switches 30, 32 and 34, the modulation output is supplied on line 18 to a resistor 50 which ultimately feeds to the oscillator 14. The oscilla- tor 14, however, must be energized in order to provide an output. It should be appreciated that a battery 52 is coupled to VCC pin of the microcontroller 16 to energize it at all times. The microcontroller 16 may, for instance, be a CMOS 8-bit microcontroller such as a Zilog Z86C03. One of the pins of the microcontroller 16 provides a pulsed output at pin 54 which is fed through a 470-ohm resistor 56 to an NPN transistor 58 which receives the pulses at its base 60, transistor emitter 62 is connected to ground and its collector 64. Current from the battery 52 may be supplied to a one millihenry inductor 70 coupled to the battery 52 and to the collector 64. A pulse on the line 54 switches the transistor 58 off uncoupling the inductor 70 from ground and causing current to flow through a diode 80 to a 10 microfarad electrolytic capacitor 82 and charging the 10 microfarad electrolytic capacitor 82 until the point that it reaches a voltage which is equal to the breakdown voltage of a Zener diode 84 connected to the capacitor 82. A 100 kilohm resistor 86 is connected between the Zener diode 84 and ground and a feedback line 88 couples the junction of the Zener diode 84 and resistor 86 to a feed¬ back input terminal on the microcontroller. Thus, when the Zener diode goes into avalanche, driving the line 88 high, the microcontroller drives the pulsed output 54 high, bias¬ ing the transistor 58 on and interrupting current flow to the capacitor 82. The capacitor 82, however, has received sufficient potential to energize the oscillator 14 as will be seen hereinafter. Referring now to FIG. 2, operation of the micro¬ controller 16 is shown therein. In a step 100 an interrupt occurs every 50 milliseconds. In a step 102, a test is made to determine whether the pulsed output pin connected to the line 54 is high. If it is high, the switched mode output on the line 54 is set low in a step 104. If the test of step 102 is negative, a test is made in a step 106 to determine whether the feedback input on line 88 is high. If it is, control is transferred to the step 104, causing the pin connected to line 54 to switch low. If it is not, control is transferred to a step 110, causing the switch mode output line connected to line 54 to switch high, turn¬ ing on transistor 58. In a step 112, a test is made to determine whether the period for the modulation bit timing for the modulation generated on line 18 has expired. If the period for modulation bit timing has expired, the routine is exited in a step 114. If it has not expired, the next bit position is obtained in a step 116 and it is outputted, following which the routine is exited in a step 118. The modulation bits supplied to resistor 50 are fed to a line 130 after having been reduced in potential by the voltage divider, including resistor 50 and a resistor 132, connected thereto. A capacitor 140, connected to ground, comprises a stabilizing filter capacitor and is connected to a series inductor 142 which blocks radiation of stray harmonics of the radio frequency in the range of 300 to 400 MHz. The modulated signal is then fed to a base 144 of an NPN transistor 146, also having a collector 148 and an emitter 150. The emitter 150 is connected through an inductor 152 for harmonics suppression and through a parallel resistor 154 and capacitor 156. The resistor 154 and capacitor 156 which are connected to ground. The resistor 154 supplies control over the DC bias and the capacitor 156 controls the radio frequency gain of the oscillator of transistor 146. The emitter 148 of the transistor is connected via a line 160 to a grounded capacitor 162, having an antenna coil connected thereto. A second grounded capacitor 164 is connected to the line 81 as well as to the antenna coil 20. The coded transmission is transmitted by the antenna 20 to a garage door operator or other device to be operated as appropriate. Attached as Appendix A is a listing of computer instructions used in implementing the present embodiment. While there have been illustrated and described particular embodiments 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 modifi- cations which fall within the true spirit and scope of the present invention. - 9 - .endm HFILL .macro TFILL TFILL TFILL TFILL TFILL TFILL TFILL TFILL TFILL TFILL .endm Interrupt Vector Table .org OOOOH .word OOOCH IRQO P3.2 n .word OOOCH IRQ1. P3.3 .word OOOCH IRQ2, P3.1 .word OOOCH IRQ3, P3.2 p .word TIMERUD IRQ4. T0 .word OOOCH IRQ5. T1 .org OOOCH __ ** _< ** «- ******* • »««*««««««♦ WATCHDOG INITILIZATION start: START: di ; turn off the interrupt for init WDH WDT ; kick the dog STACK INITILIZATION SETSTACK: clr 254 Id 255,#STACKTOP ; set the start of the stack DATA INITILIZATION BIT1TO10 Id C11,#03 ; code 33333333333 MAX POWER Id C12,#03 Id C13,#03 Id C14,#03 ; code 33333333333 MAX POWER clr CODEPOS TIMER INITILIZATION •**•••*••*• * •*•••*** * «*••»*•»»•» ••••••• Id PREO,#00000101B ; set the prescaler to / 1 for 4Mhz xtal Id PRE1,#01000010B ; one shot mode /16 Id T0,#032H ; set the counter to count 32 through 0 Id TMR,#00000011B ; turn on the timer PORT INITILIZATION **_*•*--*_**** * **-- ** *-**__ * *•_* •** _ *_**#_ _. INITERRUPT INITILIZATION SETINTERRUPTS: Id IPR,#00000001B ; set the priority to timer Id IMR,#ALL_ON_IMR ; turn on the interrupt MAIN LOOP MAINLOOP: eι ; enable interrupt Id P01 M,#P01 M_INIT ; set mode Id P3M,#P3M_INU set port3 Id P2M,#P2M_INIT set port 2 jr MAINL0OP TIMER UPDATE FROM INTERUPT EVERY 50uS TIMERUD: kick the dog test for the voltage max meet toggle the output pin ; turn off the output ; decrease the code counter ; set the count for 1mS period ; allow stacking of interrupts ; output the code iret **»**»•*»** * » • **» • * ** CODE OUTPUT ROUTINE EVERY 1mS ; set the position to the next one ; test for the last count position ; if not the last count then continue ; else reset the counter ; test for the blank time ; if not the do the code ; turn off the output ; test for second frame active time ; K the second frame then jump ; test for the first blank time ; if not the first blank time then output ; blank tiem turn off the outputs ; test for the sync ; if not do the bits ; if sync time set the output ; else turn off the output ; get the present counter ; dear the carry flag ; /2 ; dear the carry flag - 1_ - ITC TEMP /4 add TEMP,#CODE_GRP add in the off set Id BΓΠΈMP,@TEMP read the bit to output Id TEMP.CODEPOS get the position in the bit and TEMP OOOOOOHB add TEMP,BΓΠΈMP see if the output needs to be set cp TEMP,#04 jr UILOFFEXIT JP ONEXIT AF2: Id TEMP.CODEPOS remove the off set sub TEMP,#84D cp TEMP,#03 test for the sync jr ugt,ABITS2 if not do the bits cp TEMP,#00 JP ugt.ONEXIT if sync time set the output JP OFFEXΓT else turn off the output ABITS2: rcf dear the carry flag rrc TEMP /2 rcf dear the carry flag ITC TEMP IA add TEMP,#CODE2_GRP add in the off set Id BΓΠΈMP,@TEMP read the bit to output Id TEMP.CODEPOS get the position in the bit and TEMP,#00000011B add TEMP.BΓΠΈMP see if the output needs to be set cp TEMP,#04 jr ult,OFFEXIT JP ONEXIT ONEXIT: Id P0,#00000001b ; turn on the output jr CODEDONE OFFEXΠ * : Id P0,#00000010B ; turn off the output CODEDONE: ret .end

Claims: What is claimed is: 1. A hand-held radio frequency transmitter for use in generating a coded radio frequency transmission, comprising: a switched mode power supply; an oscillator coupled to be driven by the switch mode power supply; and a modulator for controlling operation of the oscillator to cause the oscillator to be modulated by coded signals.

Inventors: FITZGIBBON JAMES J, FITZGIBBON, JAMES, J.
Applicants: CHAMBERLAIN GROUP INC, THE CHAMBERLAIN GROUP, INC.
Application year: 1996
Main classification: H04Q7
IPC codes: H04B1