Created: Feb 12, 2014
No description available.
A proximity alarm is any alarm that goes off when some event occurs within a certain proximity (distance) of the detector. The majority of proximity alarms are motion sensors. Alarms may alert only you, or they may alert both you and the intruder. It may be advantageous to alert the intruders, to give them pause before going further. The noise may also be utilized to shock the intruders for a moment, creating a tactical advantage.
The HEF4049B provides six inverting buffers. The first two inverters are connected in a simple RC oscillator circuit. The frequency is determined by the values R1, C1, C2, and the internal characteristics of the integrated circuit. As long as the circuit is oscillating, a positive dc voltage is developed at the output of the voltage-coupler circuit: C3, D1, D2, and C4. The dc voltage is applied to the input of the third inverter amplifier, keeping its output in a low state, which keeps Q1 turned OFF so that no sound is produced by the BUZZER. With C1 and C2 adjusted to the most sensitive point, the pickup plate will detect a hand 3 to 5-inches away and sound an alert. Set C1 and C2 to approximately one-half of their maximum value and apply power to the circuit. The circuit should oscillate and no sound should be heard. Using a non-metallic screwdriver, carefully adjust C1 and C2, one at a time, to a lower value until the circuit just ceases oscillation: Buzzer should sound off. Back off either C1 or C2 just a smidgen until the oscillator starts up again - that is the most sensitive setting of the circuit.
This device is suitable for safety and security applications. Its motion sensing capability is useful for monitoring without the need of vision.