In this project, we show how we can use the telephone as an electronics eye. With the help of a landline phone, we check and examine the position of the house automatically. In this logic, we attach some sensors with the telephone and if there is any miss-hap, the telephone is automatically switched on. This circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This causes the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due to which the supply to the COB (chip-on-board) is completed. The signal generated by COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is wired around IC TDA 2002. The sensitivity of the circuit depends on the distance between bulb and LDR as well as the setting of preset VR1. Thus by placing the bulb and the LDR at appropriate distances, one may vary preset VR1 to get optimum sensitivity. An ON/OFF switch is suggested to turn the circuit on and off as desirable. This proximity detector using an infrared detector can be used in various equipment like automatic door openers and burglar alarms. The circuit primarily consists of an infrared transmitter and an infrared receiver. The transmitter section consists of a 555 timer IC functioning in a stable mode. The output from a stable is fed to an infrared LED via resistor R4, which limits its operating current. This circuit provides a frequency output of 38 KHz at 50% duty cycle, which is required for the infrared detector/receiver module.
[...] XTAL1 Input to the inverting amplifier and input to the internal clock operating circuit. XTAL2 Output from the inverting amplifier Block Diagram Fig Block diagram of IC AT89C Oscillator Characteristics XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip , as shown in Figure 8. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 9. [...]
[...] After 30 seconds, the device will dial up the pre-programmed telephone number, and will deliver the emergency message stored in the speech IC. The message is recorded in OTP IC so that it can be changed. We can store the message in our voice. The four major units of this project are: 1. Sensor unit 2. Microcontroller interface unit 3. Dialer circuit 4. Digital voice processor BLOCK DIAGRAM BLOCK DIAGRAM Fig Block diagram illustrating a brief working of the major units involved in the project CIRCUIT DIAGRAM Fig Circuit diagram of the project SENSOR UNIT The sensor unit consists of two sensors: Fire alarm Infrared proximity detector Fire Alarm This circuit (figure warns the user against fire accidents. [...]
[...] Therefore after the initial edge event, the interrupt may occur between 1 and 2 time-out periods later (See Figure 15). Fig Example of Negative Edge Comparator Interrupt with Debouncing Special Function Registers A map of the on-chip memory area called the Special Function Register (SFR) space is shown in the table 3 below. That not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. [...]
[...] This IC inverts the data on its input terminal and gives inverted output Number Display Unit: This unit displays the received device code from the telephone line dialed from remote section. This unit consists of a BCD to seven segment decoder IC7447 and a seven segment display. A seven segment display has seven LEDs connected in a sequence to give a regular shape and a LED to display the dot for decimal point. It has 10 pins. Out of this two pins are common for all LEDs and remaining are another polarity terminals of the LED. [...]
[...] The pin is activated when a voltage level anywhere between 0 and 0.4 volt is applied to the pin. The reset pin will force the output to go low no matter what state the other inputs to the flip-flop are in. When not used, it is recommended that the reset input be tied to Vcc to avoid any possibility of false resetting. Pin 5 (Control Voltage): This pin allows direct access to the 2/3 Vcc voltage-divider point, the reference level for the upper comparator. [...]
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