Delay Circuit Using Transistors

  

A Simple circuit that charges a capacitor on a switch press and holds the LED ON until capacitor discharge ..thus producing a delay

When the switch is pressed....the follwing happens as shown in figure below

* the current flows from resistor 

* turns ON the transistor which in turn turns ON the LED

* charges the capacitor

Analog Potentiometers v/s Digital Potentiometers

   Analog Potentiometers or Mechanical Potentiometers:

These are the standard variable resistors with sliding contact that can be varied by hand.

Digital Potentiometer or Electronic Potentiometers:

The wiper is digitally controlled by the MCU.The resistance between the 2 terminals are adjusted by the input signals

More reliable than mechanical potentiometers

Examples : AD5171 (I2C controllable ) and AD5206 (SPI controllable) 

Zener Diode

A semiconductor device consisting of a P-N which conducts the current in reverse direction when a specific voltage is reached.

Direct and Alternating current

Direct Current

The flow of current that you get from a battery is called direct current or DC.It is a steady stream in one direction

Alternating Current

The flow of current that you get from the power socket if your home is called alternating current or AC.It changes from positive to negative 50times each second.

Cranking up voltage so that so that electricity can be distributed over long distances.

AC is useful in motors and domestic appliences.

Intrinsic semiconductor

  1. An intrinsic semiconductor at room temperature has a few electrons and holes

2. The holes at room temperature are due to the thermal energy

Short Circuits

A short circuit is a direct connection between the two sides of the power source

Decoding resistors

Some resistors have their values printed on them in small print which is usually visible with a magnifying glass.

Example as below:

While most are color coded with bands.like some of these

Steps to decode a color coded Resistor

Step 1 :

The color of the resistor has no significance and hence we look only at the bands and find for a silver or gold band.This is the last band and hence it should be towards your right.

Silver means 10% tolerance while gold means 5% tolerance

Some resistors don't have a silver or gold band.In such a case you need to see the band spacing.if the bands are closely spaced then that side is ur left.

Step 2 :

Start decoding the bands as per below table from left to right.

Electricity basics

When electricity travels through a shorter distance,it encounters less resistance as a result the current increases.

The heat generated by electricity is proportional to the current that flows.

When electrons flow through a wire it is called amperage named after Andre Marie Amphere.this flow is commonly known as current and the flow of electricity per second is measured in Amphere.

The pressure of electricity that causes the flow is measured in volts named after Alessandro Volta.

Resistor and Resistance

A resistor resists the flow of electricity.

Resistance is measured in ohms which is an international unit

Resistance was discovered by Georg Simon Ohm.

Lower resistance allows more current to flow.

A higher voltage overcome resistance and increase the current.

Interesting fact

When a human tongue is moist with saliva then it has a resistance of 50k and hence we get a tingling sensation when we touch a battery to it

Insulator is a material that has a very high resistance to electricity

Conductor is a material that has a very low resistance to electricity.

Example : Copper, Aluminum, Silver and Gold are excellent conductors

Potentiometers are variable resistors which allows you to vary the voltage and current by varying the resistance.

It consists of a circular track of conductive plastic or a loop of coiled wire which posesses some resistance and as you turn the shaft of the potentiometer,a wiper rubs against the resistance.

Interesting fact

The potential difference(The voltage drop) between the cathode and the anode of a tiny old fashioned bulb varys much more than a LED as the light bulb acts as a pure resistor while an LED self adjusts to some extent, modifying it's resistance as the voltage pressure changes.

Transducer circuit topologies used in sensors

Voltage mode

high impedance voltage preamplifier is preferred in this mode.

Current mode

Includes low input impedance so that the inherent model of the transducer the connecting cable and the stray components don't affect the signal even if they are subjected to thermal variations.

It is less sensitive to electromagnetic interference.

The frequency characteristics is linear for much higher frequencies as compared to the voltage preamplifier.

When do we use PNP Transistors

 

PNP Transistors are used in circuits when where negative voltages are involved.

Example : AC signal Amplification

Commonly used symbols in Timming diagrams

Most of the electronic device outputs anf inputs are depicted by Timming diagrams.

And hence reading then effectivly in the practical world is a crutial skill

Here are some common symbols used in Timming diagrams

Light Emitting Diodes

The longer wire protruding from the LED must receive a more positive voltage than the shorter wire

The voltage difference between the two wire and the current passing through the LED should not exceed the limit specific by the manufacturer.