Magnetic field sensor for use in a security alarm system

Abstract

A proximity sensor comprises a magnet which generates a magnetic field and a magnetic field sensor. The magnetic field sensor includes a radio and an antenna which can transmit an output signal on a plurality of output frequencies. A microprocessor is programmed with a plurality of data protocols. Each of the output frequencies operates on at least one of the data protocols. There is a dip switch which is actuated to provide a code to the microprocessor. A data protocol is implemented by the microprocessor based on the code. There is a MEMS oscillator programmed to a discrete frequency based on the data protocol implemented by the microprocessor. The MEMS oscillator provides the discrete frequency to the radio. The radio is provided with single phase-locked loop which generates the output signal based on the discrete frequency. The single phase-locked loop may be a ×32 multiplier.

What is claimed is: 
     
         1 . A magnetic field sensor, the magnetic field sensor comprising:
 a microprocessor;   an indicator which turns on when a magnetic field is sensed and turns off when a magnetic field is not sensed, and wherein the microprocessor renders the indicator inoperable a predetermined period of time after the magnetic field sensor is powered up.   
     
     
         2 . A magnetic proximity sensor including a magnet which generates a magnetic field and a magnetic field sensor, the magnetic field sensor comprising:
 a microprocessor;   an indicator which turns on when a magnetic field generated by the magnet is sensed and turns off when a magnetic field generated by the magnet is not sensed, and wherein the microprocessor renders the indicator inoperable a predetermined period of time after the magnetic field sensor is powered up.   
     
     
         3 . A magnetic proximity sensor including a magnet which generates a magnetic field and a magnetic field sensor, the magnetic field sensor comprising:
 a radio and an antenna which can transmit an output signal on a plurality of output frequencies;   a microprocessor programmed with a plurality of data protocols, each of the output frequencies operating on at least one of the data protocols;   a dip switch which is actuated to provide a code to the microprocessor, and one of the data protocols being implemented by the microprocessor based on the code; and   a MEMS oscillator programmed to a discrete frequency based on the said one of the data protocols implemented by the microprocessor, wherein the MEMS oscillator provides the discrete frequency to the radio and the radio is provided with single phase-locked loop which generates the output signal based on the discrete frequency.   
     
     
         4 . The magnetic field sensor as claimed in  claim 3  further including a shunt at each terminal of the antenna. 
     
     
         5 . The magnetic field sensor as claimed in  claim 3  further including an indicator which turns on when a magnetic field generated by the magnet is sensed and turns off when a magnetic field generated by the magnet is not sensed, and wherein the microprocessor renders the indicator inoperable a predetermined period of time after the magnetic field sensor is powered up. 
     
     
         6 . The magnetic field sensor as claimed in  claim 5  further including a circuit board and a housing with an opening:
 wherein the dip switch and the indicator are mounted on opposite sides of the circuit board; and 
 wherein the circuit board is disposed in the housing with the dip switch being accessible though the opening.