Simple Human Interference Detector

PIR it stands for passive infrared. PIR sensors detect the infrared radiation from the object. PIR does not detect any heat radiation from any objects. It only detect infrared radiation. PIR sensors mainly used for presence of any object. Mainly for human presence.

This is a simple human interfernce detector. Here we using PIR sensor and BC547 npn transistor. Normaly the PIR sensor output is approximately 1.7V. When any object presence the output of the PIR become approximately 3.8V. Here we using the switching action of npn transistor. When enough bias voltage is come to base terminal the transistor became ON. Here we using a bias resistance of 22K. Because of this bias resistance transistor Q1 is ON only when more than of 2.5V is arrived on the base terminal. So that only any object interference made the transistor Q1 to ON state. After Q1 ON it bias the Q2 transistor and it also became ON. And the indicator LED became glow in the presence of a human. Here we using transistors as Darlington pair for drive amplification purpose.

Components Required

U1- PIR
Q1,Q2- BC 547
D1- LED
R1- 22K

COMPARISON OF SCR BJT MOSFET

We all know about SCR, BJT, MOSFET here we going to familiarize the different characters of each one.

• SCR

It is also called thyristor.
 It have 4 terminals.
Minority carrier device.
High voltage high current device.
Low switching speed.
Low resistive input impedance.
Only single pulse required for turn on.
Can be connected in series easily with voltage equalizing circuits.
It have thermal run away.
Can be paralleled with forced current sharing circuits.
Most robust devices.
Less temperature sensitive.
No second breakdown.

Phototransistor

It is the device which works on the principle of absorption of of light is phototransistor. Which is more sensitive than a pn photodiode. The phototransistor is an npn transistor usually connected in  CE configuaration with the base kept open. The radiation is allowed to fall near the junction.
If light radiation is now to fall near th collector junction additional minority carriers are photo generated. These carriers contribute to the reverse current in exactly the same manner, as do the thermally generated minority carriers.

WORKING OF GENERAL TRANSISTORS NPN & PNP

We all know about the transistors they have most important role in electronic field. Here am going to explain about how the transistor work , both PNP and NPN. Mostly the transistors used as switches in electronic circuits.

 NPN means two N layers are sandwitched between one P layer. N region are rich in  with free electrons . And P region have holes and less number of free electrons. P region is the base in NPN transistors. When NPN  transistor in free state they don't have connection with collector and emitter because of the P region between it.