Doorknob Proximity Alarm :  Reverse engineered circuit diagram of a popular retail doorknob alarm. It contains a small transmitter and the doorknob acts as an antenna so it will not work on a metal door. When a person comes close to the doorknob this loads down the oscillator and the alarm sounds. The proximity sensor circuitry is perfectly capable of driving 74HCT series CMOS logic instead of the noise maker IC's shown in the circuit diagram.  (added 2/05)

DTMF Proximity Detector:  (electronic Circuit / Schematic added 10/04)

Dual Comparator:  forms temperature-compensated proximity Detector (app note added 8/03)

Dual Comparators Stabilize Proximity Detector:  02/16/98 EDN-Design Ideas / (added 3/03)  

Infra-Red (IR) Beam Alarm/ Proximity Detector:  This circuit can be used as an Infrared beam barrier as well as a proximity detector.  The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets.  The receiver consists of a 555 timer IC working as an oscillator .... (added 6/06)

Infrared Level Detector for Liquid Level Detection and Proximity Detection:  Useful for liquids level detection and proximity devices Up to50 cm. range, optional relay operation (added 6/06)

Magnetic proximity sensors:  (electronic circuit added 10/05)

Magnetic Proximity Switch:  (electronic Circuit / Schematic added 10/04)

Optical Proximity Detector:  A "reflector" isolator (A) detects the presence of an object by bouncing light off of it. This technique is useful in circuits that detect when an object is close enough to the sensor (B). (added 3/03)

Proximity Alarm #2:  (circuit / schematic added 2/03)

Proximity Alarm #3:  (electronic Circuit diagram added 03/03)

RS-232C Link Monitors Animal Activity:  11/06/97 EDN-Design Ideas / (added 3/03)