week 6 (FYP 1)

For this week, I'm research about sensor, because I using various sensor in this project. Main focus of this week are about :

1. Proximity sensor

2. Smoke detector 

3. Vibration sensor 

A sensor is a device which measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, all sensors need to be calibrated against known standards.

• PROXIMITY SENSOR 

The proximity sensor used in this project is a long range IR transmitter circuit. This is an ULTRASONIC SENSOR work on a principal similar to radar. Here a detector circuit is used that will give long range detection.

Fig. Schematic diagram of Proximity Sensor

CIRCUIT DISCRIPTION OF IR TRANSMITTER

The circuit uses three infrared transmitting LEDs (IR1, IR2, and IR3) in series to increase the radiated power. Further to increase directivity and power density, in circuit, IR LEDs inside the reflector of torch can assemble. For increasing the efficiency a MOSFET (BS170) is used, which acts as a switch and thus reduce the power loss that would result if a transistor were used. To avoid any dip during its “ON/OFF” operation, a 100μF reservoir capacitor C2 is used across the power supply. Capacitor C2 supplies extra charge during switch on operation. As the MOSFET exhibits large capacitance across gate source terminals, a special drive arrangement has been made using NPN-PNP DARLINGTON PAIR of BS547 and BS557 (as emitter follower), to avoid the distortion to the gate drive input.Data to be transmitted is used for modulating the 38 kHz frequency generator by CD4047 (IC1). In the receiver section, TSOP1738 is used for efficient reception. The transmitter circuit transmit the IR waves towards the target and in receiver section, receiver receive the IR signals with variations and give suitable output to the microprocessor.

• SMOKE DETECTOR 

As it is mentioned previously that smoke detector is a circuit that used to detect any smoke in the particular range. Smoke detector circuit uses an IC 555 that is a timer IC. This circuit uses a very simple approach to detecting smoke in the air. It uses an LDR (Light Dependent Resistor) as a light detector. As fire smoke comes across the LDR range, the resistance of the LDR changes, which in turn trigger an alarm. Concept applied to project: LDR is enclosed in a cylindrical case so it remains in dark and having a high resistance in normal conditions. When smoke enters in this case LDR resistance decreases and hence desired output is obtained.

LIGHT DEPANDENT RESISTOR (LDR)

A light-dependent resistor, alternatively called an LDR, is a variable resistor whose value decreases with increasing incident light intensity. An LDR used in circuit, is made of a high-resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. In the circuit, as the LDR detect the light variations due to smoke, it gives the output to the IC555 and timer IC produce a trigger alarm. From the above discussion, it is clear that the smoke detector circuit detect the smoke and gives the trigger alarm to the output.

• VIBRATION SENSOR 

Vibration sensor are many type but I am sharing with you only accelerometer vibration sensor meter Working principle: measure the rate at which the velocity of an the object is changing . The vibration sensor is used for testing the impact force. It has high vibration detection sensitivity and the environmental of sound signal suppression, which has strong ability to engage in interference. Used as a security and alarm to measurement Specialties is a leading global provider of accelerometers and vibration sensing know-how to key customers in the transportation, aerospace, medical, general laboratory, and auto safety industries.

Fig. vibration sensor

This sensor uses open-collector output transistor drive mode, you can directly interface with MCU. Connecting the white line (output) to arduno/MCU‘s digital I/0, then upload code . First set the port of MCU as”1”(high),then pull -up resistor (R7)output DC12v.When the sensor detect the vibration signal,Q1 break over. The voltage of a drop from 12v to 0.1v and white line drop-down to 0.8v, while MCU can detect low voltage. Used as a security and alarm.(motor vehicles, safety box, treasury doors and windows etc.)

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sh mohd faiz