| 摘要 |
A secure, keyless secondary transmitter unit for use in an automatic garage door operator transmits a code set by a code setting device as modified by digits entered at a keyboard. A controller constructs an identification code by inverting bits of the code set by the code setting device that correspond to entered digits. A radio frequency transmitter transmits this altered code in the manner of known automatic garage door operators. Thus operation of keys corresponding to the bits that differ between the receiver code and the secondary transmitter code controls the door. The keyboard preferably also includes an entry complete key indicating entry of the complete digit sequence and a clear key to restart the digit sequence. A lamp connected to the controller illuminates the keyboard upon operation of any key at the keyboard and is turned off if no key is operated in a predetermined period of time. Further operation of the entry complete key within this predetermined period of time causes the controller to again construct and transmit the same code. This secure keyless transmitter unit is believed to be as secure as the primary transmitter units, even when permanently mounted outside the controlled door.
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