ZigBee is a wireless networking standard that is aimed at remote control and sensor applications which is suitable for operation in harsh radio environments and in isolated locations, It builds on IEEE standard 802.15.4 which defines the physical and MAC layers. Above this ZigBee defines the application and security layer specifications enabling interoperability between products from different manufacturers. In this way ZigBee is a superset of the 802.15.4 specification.With the applications for remote wireless sensing and control growing rapidly it is estimated that the market size could reach hundreds of millions of dollars as early as 2007.This makes ZigBee a very attractive proposition, and one, which warrants the introduction of a focused standard.
Refrigerator Door Alarm
It is very essential to keep the door of fridge closed all the time. The refrigerator will not work efficiently if the door is left open. To avoid such situations, this [[wysiwyg_imageupload::]]project presents an interesting circuit that will sound an alarm if the door is not properly closed This alarm circuit will not buzz till the door is opened and closed between the predefined times but if it crosses the predefined time it will start buzzing. NAND Gate is created by applying NOT operation to an AND gate. Hence, the outputs of this gate are opposite to that of AND gate when the inputs are kept same. This simple circuit project is based around transistor, switches and NAND gates. In the standby mode, the switch is closed and the current flowing through R1 is grounded through the switch.
Security Alarm for Doors, Almirah, cupboards using Opam
The circuit gives an audio visual alarm when somebody enters from a door. This project can also be used in locker and almirah door. This circuit is based on [[wysiwyg_imageupload::]]operational amplifier LM741 and LDR. An op-amp produces an output voltage that is hundreds of thousands times larger than the voltage difference between its input terminals. The circuit comprises of Operational amplifier A741 which is used as sensitive voltage comparator, LDR and Preset VR1. The preset provides reference voltage to the non-inverting terminal pin 3 and LDR. R2 is connected to inverting pin 2 of IC1. How does the alarm sense someone entering? How is the circuit constructed? What is the role of op-amp in its working? Continue reading to find out how answers to these questions and more.