The Design Corner / Hobby Corner - Electronic Field Disturbance Monitor
designed by David A. Johnson, P.E.
Updated on:  Thursday, December 17, 2015 01:44 PM

  Electronic Field Disturbance Monitor:  Introduction - Monitor Design - Monitor Operation

Circuit Description:    Front-end Circuit Section - Alarm Threshold Detector 
Power Supply Voltage Regulators
Battery Voltage Monitor - Monitor Assembly
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Field Disturbance Monitor Design

The field disturbance monitor I designed is illustrated in Figures 2 and 3 below. It uses a telescoping whip antenna that is mounted on top of a metal box, to probe the air for field changes. By raising and lowering the antenna you can increase or decrease the field change sensitivity. The design I chose uses an off the shelf metal box to house the electronics. The circuit is powered by a standard 9 volt battery. Three LED light emitting diode indicator lights provide system status. One of the LEDs indicates a positive field change while another indicates a negative field change. A third power indicator light doubles as a battery voltage indicator. If the light fails to turn on, it is an indication that the 9 volt battery needs to be replaced. An alarm sensitivity dial can set the minimum disturbance level to trigger an alarm. A loud piezoelectric type beeper sounds whenever the alarm level is exceeded. A toggle switch allows the alarm feature to be turned off. An output jack at the rear of the monitor can be used to connect the monitor to a remote alarm device if desired. I have also included a output jack that can be used to send the monitor's processed disturbance signal to some remote recording device. Finally, to insure consistent operation, an earth ground jack is also included at the rear of the monitor's enclosure. Connecting the ground jack to a true earth ground improves disturbance sensitivity.

Component placement, front of metal box Component placement, rear of metal box
Figure 2 Figure 3

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