V. LOW BATTERY SENSOR The function of the low battery sensor schematic is to measure the amount of battery life remaining; when the battery life dips below 3.5V the design enables smoke detector to emit the low battery alarm via the tone generator.
VI. TONE GENERATOR AND SPEAKER The tone generator and speaker module emits the appropriate sound determined by the PIC microcontroller. There are four distinct alarms [7]. The temperature detector alarm and smoke alarm both sound at 4 kHz; however the
temperature alarm is sounded at a higher volume level. In addition, there is a detected signal alarm (smoke or fire detected at another detector) that sounds at 2 kHz. There is also a low battery alarm that sounds at 500 Hz.
VII. RECEIVER The receiver (RMX-900-HP3) receives the signal from the transmitter of the other smoke detectors and relays that signal to the PIC microcontroller.
VIII. PIC MICROCONTROLLER PIC microcontroller (PIC 16F84A) is the heart of the system. Microcontroller input comes from receiver, temperature sensor, smoke sensor, and low battery sensor as well as outputting the appropriate signal and bits to the tone generator and transmitter.
IX. TRANSMITTER The transmitter (TMX-900-HP3) sends a signal to the other smoke detectors in the network in order to alert them to set off the audible alarm.
X. RF TRANSMISSION Radio frequency (RF) transmission uses radio waves like radio or television signals to transmit audio via a carrier from transmitter to receiver. The transmitter has an antenna usually attached to the transmitter unit, which needs to be positioned adequately cover the listening area. Transmitter and receiver communicate between them through Manchester coding for RF transmission. Manchester coding works on transitions from high to low (for bit 0) and low to high (for bit 1). The actual width of the pulses doesn’t matter particularly (within reason).Packet system transmission in terms of reliability. The packet consists of a no. of different sections.