Remote vehicle access featuring high security

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention, as illustrated in FIG.
1 in block diagram form, includes a transmitter 10 featuring command inputs 12a, b, c and d, which may be used to selectively provide input signals to microprocessor 14.
In the preferred embodiment of the present invention, microprocessor 14 comprises a MOTOROLA 68HCO5J1 having inputs 12a, b, c and d which comprise conventional contact type switches.
Closure of any of the contact switches produces an input signal which represents a command which causes memory 16 to produce a series of signals having a unique signature which correspond to the respective input command which is then supplied to oscillator 18 which implements the series of signals in the form of radio frequency signals suitable for broadcast by antenna 20.
Oscillator circuit 18, shown in FIG.
2, comprises transistor Q1, resistors R1 and R2, in addition to capacitors C1 and C2.
SAW1 stabilizes the frequency of oscillation of circuit 18 to preferably 434.
09 MHz.
SAW1 is a SURFACE ACOUSTIC WAVE RESONATOR having an equivalent model illustrated schematically in FIG.
3.
Antenna 20 broadcasts the signal generated by circuit 18 for any duration which voltage is supplied to node N.
The magnitude of voltage supplied to node N can be varied from B+ to any portion thereof by selection of any particular output or combination of microprocessor 14.
For example; output A of microprocessor 14 includes resistor RA which provides a first magnitude bias voltage to oscillator 18.
Output B of microprocessor 14 includes resistor RB which provides a second magnitude bias voltage to oscillator 18.
If output A and B are both "on", a third magnitude bias voltage will be supplied to oscillator 18.
In the preferred embodiment, RA and RB are 3.
9K ohm resistors; a first bias is provided by output A; and a second bias is provided by the combination of outputs A and B.
When output A is provided to bias oscillator 18, oscillator 18 produces a 434