Surges and Spikes

Air conditioners, Refrigerators, and Elevators are high-powered equipment. This equipment has motors and compressors and they require a lot of energy to switch on and off. 

The sudden switching causes surges and spikes on the power line & if not properly handled then these can damage the device or machine. 

Power-line surges can easily reach 6,000 volts. A power surge or a spike is an increase in voltage significantly above the standard voltage of 230 volts.

A Surge lasts 3ns or more. 
A Spike lasts 1-2 ns.


Surge


Spike

In order to protect our devices from the above cases, we need to build a Surge Protector. We make it by combining 2 electronics components named Varistor & Fuse 

Varistor

A varistor is a special type of resistor that is used to protect circuits against high transient voltages. A varistor is also known as VDR ( Voltage Dependent Resistor ) 


                   



                                    
Under normal conditions the resistance of the varistor is very high. When the connected voltage gets higher than the specification of the varistor known as the Clamping voltage, the resistance immediately gets extremely low thus current starts to flow through it 

Fuse

When High current flow through a fuse it melts and makes the circuit open 


Combining the above 2 components we make a surge protector. Fuse is in series and VDR in parallel. 

surge protector

The varistor is simply connected between line and neutral but after the fuse. If the voltage across varistor exceeds it's threshold then it acts as a short circuit thereby making high current flow through the fuse which in turn gets melted and open resulting disconnection of the Appliance from the mains supply 


For 230 V mains a varistor of 275 V clamping voltage is a good choice.

                                                 








SPI (Serial Peripheral Interface ) communication between 2 AVR mcus

SPI stands for Serial Peripheral Interface

SPI  is a communication protocol used to communicate between microcontrollers and other devices, like other microcontrollers, external EEPROMs, DACs, ADCs, etc. With this interface, you have one Master device which initiates and controls the communication, and one or more slaves who receive and transmit to the Master

Project description 

This project shows SPI communication between 2 atmega8 mcus in which 1 atmega8 is master and the other one is a slave.

Here two MCU will transfer the byte to each other via SPI and will show the received byte at the output port

Sequence
  1. master atmega8 will transfer 112=01110000 to the slave atmega8
  2. slave atmega8 will transfer   21=00010101 to the master atmega8
  3. so master atmega8's PORTD should show 21=00010101
  4. So slave atmega8's PORTD should show 112=01110000
  5. master and slave prepare the data to be sent in their respective shift registers & the master generates the required clock pulses on the SCK line. MSB goes first.


ckt & codes are here : https://drive.google.com/file/d/0B8PCKc-8AIcDMEdOa3NwZnhVeWM/edit?usp=sharing

4x4 matrix keypad interfacing with atmega8

This project shows how 16 keys are multiplexed by 4x4 matrix way i.e no of rows: 4 & no of columns: 4 & interfaced with an AVR mcu. 

Atmega8 is used here along with a character LCD to show the pressed key value of the matrix keypad.



Dot Matrix Display interfacing with Microcontroller

" Sync electronics" - message is displayed at Dot matrix by scrolling using 74HC595 shift register .... the circuit given is just for showing how 2 dot matrix units should be connected to a microcontroller through the shift register. If more dot matrix displays are needed then more shift registers are needed. 

Note: Circuit will not simulate; the circuit is just for showing the connections required; one has to build the circuit in real and then test  

8*8 Dot matrix
5*7 Dot matrix


Ckt & codes are here : https://drive.google.com/file/d/0B8PCKc-8AIcDNjU3ZWc2ZEF0VDg/edit?usp=sharing

74HC595 shift Register interfacing with atmega8

This is a simple project for interfacing the 74HC595 shift register with the Atmega8 microcontroller. An 8bit pattern is displayed by writing 8bit unsigned int type data to 74HC595 ic 

this project will help understand multiple DOT matrix displays interfacing with the microcontroller.





Coupling vs Decoupling

The capacitor is a basic electronic component capable of storing electric charges. It is made of an insulator attached by 2 metal plates on both sides. Today we will know about 2 important use cases of capacitors. But first a reminder, do not get confused by bringing on the concept of AC capacitor (non-polar) here. Just think that we are talking about DC capacitor (polar) only. 

Decoupling capacitors: 

Until Capacitor is fully charged Direct Current can flow through the capacitor for a short period of time. The idea is to use the capacitor in such a way that it shunts/is connected in parallel. 
  • They oppose quick change of voltage.
  • They are used to filter out the AC component  
  • Decoupling capacitors added to the circuit in order to smooth out the power supply voltage.
  • An alternative name is bypass capacitor. 

Coupling capacitors:

Alternating current switches it's direction with a certain interval thus making the capacitor charged and discharged. So if the capacitor is connected in Series AC will flow through the capacitor. 
  • Used to filter out the DC component of the signal
  • In analog circuits, coupling capacitors are extensively used in amplifiers. 
  • The voltage bias of a transistor is crucial for the normal operation of the amplifier. ac signal is fed to the base of a transistor where the capacitor is in series (this mode is called coupling ). 
  • The role of coupling capacitors is to prevent the incoming AC signal from interfering with the bias voltage applied to the base of a transistor.

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