12 V DC POWER SUPPLY

Today I am going to make here a 220 Volt AC to 12 Volt DC  Power supply.

For that we must be familiar with the conversion of  high voltage AC to low Voltage AC.A transformer is used for the conversion, which is the combination of two coils mutually coupled together using a ferrite core, Which is a soft iron core.One coil is of large numbers of turns with high resistance of small diameter of copper wire, which is called high voltage coil and another coil is of low resistance ,low number of turns but with comparatively large diameter of copper wire,which is called low voltage coil.

TRANSFORMER TEST-

Before using the transformer we must know which coil's terminals should be connected to mains or circuitry.It is important since this knowledge would protect your home wiring as well as protects your transformer  from being burned or damaged.

Now have a multimeter  (analog or digital) with you and set it to ohm measurement,now test each coils terminals,see that what readings you get.

If you are getting a reading in few kilo-ohms then it must be the high voltage coil or primary coil.

If you are getting a reading in only ohms then it must be the low voltage coil or secondary coil.

Also test for the shorting of the coils by checking the resistance of both the coil is infinite or not,If not then the transformer is faulty, just change the transformer.

Also test for the coil and core resistance is infinite or not,If so then be aware that you can get shock if you don't take care of it.It is recommended that you must change the transformer in such condition.

BUILDING THE DEVICE-

Here is the list of components-

:: Four 1N4001 diodes

:: one 9-0-9,500mA transformer

:: one LM7812 IC

:: one 470uF,50v Electrolytic capacitor

:: one 10uF,25v Electrolytic capacitor

:: one 0.1uF ceramic capacitor

:: wires

:: shoulder and shouldering iron

:: A perforated copper board or a copper clad board with 5cm By 5cm                  dimensions.  

:: A 10 cm by 10 cm cardboard

Make a bridge rectifier (see here how to make bridge rectifier) on the perforated board now take the transformer secondary or low voltage coil terminals as the rectifier AC input.The 9-0-9 has three terminals of the low voltage coil,leave the zero potential or common terminal of the coil and take the other two terminals.Always remember that a transformer output gives an AC voltage which has no polarity so don't worry of the connection at the rectifier input,it can be connected at any polarity as the input to rectifier.

Now the output of the bridge rectifier is always fluctuating DC, for knowing the polarity test it with the multimeter.You can also know the polarity by seeing that the same p terminals connected together will have negative output and vice-versa in the bridge rectifier.

Now after knowing the polarity, connect the 470uF capacitor in parallel to the bridge rectifier output.Before connecting also see the polarity of the electrolytic capacitor and connect with the same polarity as the bridge output.The black line near the terminal shows that it is negative terminal.

If the electrolytic Capacitor is connected with wrong polarity then the capacitor may explode.Also connect another 10uF electrolytic capacitor in parallel with the 470uF capacitor with correct polarity.

Now connect the positive terminal of the capacitor to the input or first terminal of the LM7812 IC and other terminal to the ground terminal or second/middle terminal of the IC. Now take the output at third/Output terminal of the IC w.r.t. the ground terminal.For stability Connect 0.1uF capacitor in parallel to the output terminal and ground terminal.Take the output across the 0.1uF capacitor.

Now fit all the circuitry on the cardboard and use it for any electronic application, Which requires 12v dc and 400mA of current.For high current applications just add a heat sink to the LM7812 IC.

You can also mount the components on a copper clad board PCB (See here how to make PCB).

Here are some pics of the Device-

HOW TO MAKE PCB OF AN ELECTRONIC CIRCUIT USING EXPRESS PCB

Hi friends today i will tell you about pcb making of an electronic circuit. To temporary make the circuit some persons use perforated boards to mount and shoulder the components. But to make permanent circuit we use copper clad board so as to ensure less wear and tear with the pcb. Some of you might have seen the pcb inside various electronics equipment e.g., T.V. , Radio, etc. We will make pcbs similar to that with perfect outline of the tracks as it has been manufactured from a company. Now first of all you must know the circuit diagram of electronic gadget you are going to make. The circuit schematic is drawn on the paper with the pin connections of different terminals of  electronics  components. The circuit diagram  helps   us for accurate making of pcb layout with right pin connection.Now the express pcb software is used for drawing the schematic in express SCH portion of the express pcb software and after making,Its printouts is taken and the circuit schematic is obtained in this way.For making the circuit schematic you must install the express pcb software (Download here free).Now after installation you will find two icons viz. expressSCH and expressPCB.The former is used for drawing the schematic,  Now double click  the the former icon and a window will appear showing various tools and drawing area.You can choose any of the ICs and electronic component from the menu.The component Menu comes when you click on the analog icon on the tool bar. Then you choose the required component or IC. Now after choosing the correct item you can place it on the work area.The component Menu contains various ICs with their part numbers and company name also like Texas instruments     SN75160, Linear Technology LT1070, Atmel Microcontrollers, Microchip PIC microcontrollers series ICs,and many more are there in the component Menu.You can choose your desired ic of which you are going to make the circuit.The ICs contains all the associated Pin with names Labeled. If the component is not listed in the Menu Then You can create your own component using Various tools in the tool bar, these component are at no.9,10,11 Position from the upper most tool.Get the information of making the custom component in the Quick start Guide of the Express SCH. You can connect the various components pins using the Connecting wire Icon from tool bar at left.Now according to the Datasheets and application notes of the components and ICs make the correct connection with wire tool. When the circuit is complete you can print the whole circuit on paper and obtain the schematic, and save the .sch file. Now double click on the express PCB icon and you will find there a toolbar,Menu bar,In The toolbar you will find a component Menu tool in the shape of an IC. You can then select the proper component and place it on the work area.Different connectors and different IC packages are available such as SOIC package,QFN package,DIP Package ,etc.This Creates a versatile ways of designing your pcbs. Now select the Wire tool for connecting different pins of the components, Also you Can link your .sch file in the ExpressPCB for Pin Connecting aid.However it is recommended in large circuit since the chances of wrong pin connection are high as compared to small circuits.It is not necessary to link the .sch file to ExpressPCB also it is not necessary that you draw schematic in ExpressSCH  for small circuit you can take a look at pin connection by hand made schematic. For linking the .sch file go to File option in the Menu bar and select 'Link schematic to PCB' .You can also configure the track width and it curvness.It is recommended to use keyboard keys for proper placement of component and wires for a perfect layout.Also the thermal pad option is available and the top layer and bottom layer option is available.You can make the custom components if it is not available in the component list. For procedure of making the custom component see the 'Quick guide of ExpressPCB' .Now after completing the layout Go to print option in the File option in Menu Bar or use short cut keys ctrl+P. Here  If you have make the pcb layout in both top layer and bottom layer then you can choose either one or both at a time.You must mention or choose the paper size for printing like A4,A3 ,etc.The paper that you use for printing must be a Butter paper or a magazine paper and the printer that you use must be the Laser printer.If you Don't have a laser printer then select in the printer option 'Windows XPS document writer'  and click ok. You will get a .xps file which you can take in pen drive and go to a photostat shop or cyber cafe that have a laser printer and print the layout on the butter paper or magazine paper. Always see the component datasheet for the proper size of the package of ICs or component you are going to use in your circuit.Also Read the Quick Guide of the softwares.Here is the Pcb Layout Of a Transmitter and Receiver Circuit Using HT12D and HT12E and RF Modules in ExpressPCB.

Here is the pcb layout of Transmitter and Receiver Circuit Using HT12D and HT12E and RF Modules which is ready for printing.

The above layout is from .xps file of the circuit.Now after printing the .xps file on Butter or magazine paper.Keep the following list of items ready for pcb making-

:: Copper clad board   (desired size)

:: Ferric chloride         (depending on size of board, dissolve 10gm in water for 50 by 30 copper clad board)

:: Electric Iron

:: Thinner

:: permanent marker  (for error correction) 

Now take the copper clad board of the size a little greater than the pcb layout.Now cut out the extra paper in the margin of the printed paper and then put in over the copper clad board where the copper is present with the printed side touching the copper surface.Before placing the paper rub the copper side of copper board with the help of scotch-brite available in market and clean the board with the help of cloth.Now pre heat the clothing iron for five minutes then place it over the magazine or butter paper below which the copper board is present.And apply lot of pressure and heat for 10 minutes and then take the board carefully since it is hot.You will see that the paper has sticked to the board then wash the paper with lot of water and remove the extra paper.You will see that the toner has been transferred to the board i.e. the whose layout has been transferred to the board.Also verify the design that all tracks are right or not,if you find any incomplete track then correct it by using permanent marker Keep the ferric chloride solution ready and dip the printed board in the solution for fifteen minutes (Eaching Process). Here are some snapshots-

Below is the Dual H-Bridge for Motor direction control used in remote control car.Its layout is not shown here.

Below is the PCB Layout of above circuit in express pcb.

Here is PCB layout from .xps file.

Here is the PCB in Ferric Chloride solution-

When Fifteen minutes has completed take out the pcb from the solution with the help of gloves and wash it with water.Now clean the pcb with thinner you Will notice that the extra copper has been removed and your pcb is ready for drilling.Drill the holes using hand drill or stand still drill at appropriate places where the components are to be placed. Use appropriate size of drill bit normally use 1mm bit.After drilling your pcb is ready to be used for placing components and shouldering.But before making the PCB layout of the circuit test the circuit on a breadboard.Here are the pcbs of the layout shown in this article.

Below is the H-Bridge circuit PCB.

Below is the Transmitter circuit PCB.

Below is the Receiver circuit PCB.

You can use the vast varieties of PCB designer software Only the difference lies is the operation of software but the procedure is same printing,transfering,eaching process etc. are same.Be careful with Ferric Chloride since it is highly corrosive.It is recommended to use gloves for treating with Ferric Chloride.

HOW TO MAKE A REMOTE CONTROL CAR

A Car consists a motor to give it forward and backward motion and its extended version would consist of another function of left and right motion which also require second motor. Therefore a car can have a minimum of Four Functions viz. Forward(Turbo), Backward, Left and right motion. The forward motion of the car is also termed as turbo because in this motion the driver takes full advantage of car as car lover already know.The car motor is powered by a dry 12v or 6v battery so that maximum torque and speed combination is developed in the motor.If the car is wired then it is easy to make it and run it but you have to move with the car also and there is always a chance of wear and tear of the car wire control of the car.The wired car range of running forward is less as compared to wireless car.It cannot move to farther distance like wireless car ca do. Hence there is a need of having wireless remote control car but it market cost is quite large, why not make your own cheaper wireless remote control car with some electronics knowledge and component available in the market are cheaper then the actual remote control car. First of all you should have the knowledge of various  electronics components  like transmitter and receiver module. In india 315 Mhz and 433 Mhz band is allowed as general purpose frequency band for common people use.Hence transmitter and receiver module are available in this range of frequency bands.The transmitter and receiver module are nothing but premade pcbs by using different amplifier stages and op amp ic and totally depend upon manufacturer.The transmitter module is usually smaller in size than receiver module and have Four terminals or pins  viz. Vcc , Data in, Ground and Antenna.The Receiver Module also has four main terminals Vcc, Ground, Antenna and Data out.

Transmitter module (left) and Receiver Module (right)

They work on ASK  (Amplitude shifting Keying) Modulation.It is a type of digital modulation. ASK is a form of Amplitude modulation which represent digital data as variation in amplitude of a carrier wave.The amplitude of the carrier changes according to the digital baseband signal.

I recommend you to study the transmitter and receiver module datasheet once only to know about its working and its rating.You can buy the modules either from eBay or from Delhi chandni-chook electronics market (for indians).I have bought three pair of modules worth Rs.525 (each Rs.175), from Shop no-594.  

Now the next thing you must know about is the Encoder HT12E and Decoder HT12D ic which are most important part of the RF circuit.The encoder ic is the ic for taking input through it four pins viz. 10,11,12 and 13 pins of the ic These pins are the data pins and denoted by  AD8 ,AD9, AD10 ,AD11.These pins have to be connected to  ground through push buttons.The Address pins 1 to 8 is used to provide the address of the transmitter and the Decoder ic must have same address so as to interact with the transmitter .The encoder in simple words is the multiplexer which encodes or multiplexes the signal along the same band of channel.It increases the total capacity of the channel band.They are available as 4 bit encoder.Here is the pin diagram of HT12E with transmitter module. The Dout is the four bit data with the 8 bit address multiplexed with it.The encoded signal is given to transmitter module Data in pin for the transmission the the ASK signal.

Now let us talk about HT12D ic.It is a decoder ic and is used to demultiplex the received data from receiver module.The HT12D ic does the reverse of HT12E ic.It decodes the received data into useful four bit information for remote control application.The decoder address pin connection must be in same configuration as that of encoder ic,otherwise it may not decode the received data into useful information.Here is the pin diagram of HT12D ic with Receiver module.

The receiver module receives the signal and give it to the Din pin of the decoder ic.The decoder ic decodes the data given and provide the four bit useful data at pin no. 10,11,12,13.Which is used for remote control application.

The data is serially transmitted and received.

Now the next ic you must be familiar of is the Quadruple Half H-Drivers Ic which is the LD293D Ic.It has four H-bridge Drivers and is used in controlling the forward and backward motion of motors.You Must read the datasheet of all the ICs discussed in the article.Here is the pin diagram with application.

Th Driver Ic has 16 pins in which pin no. 4,5,12,13 are ground of the Ic and pin no.16 is the ic supply voltage and Pin no.8 is the motor supply voltage.Pin no. 3 and 6 are enable for the motor bridge circuit and must be connected to the +5 volt supply so as to enable the H-bridge.Pin no. 3,6 and 11,14 are the output for motor terminals.Pin no.5,7 are used for controlling the forward and backward motion of the motor connected at pin no.3,6 and pin no.10,15 are used for controlling the forward and backward motion of the motor connected at pin no.11,14.

The next Ic is the 5 volt supply Ic which is LM7805 ic.It takes battery terminal voltage input greater than 7 volt and less than 36 volt And convert it into 5 volt.Here is the circuit diagram.

Now we have Enough Knowledge about the components to be used.Here is the List of components required For making the Remote control car.

:: LM7805   IC                                                           2nos

:: LD293D   IC                                                           1nos

:: HT12D     IC                                                           1nos

:: HT12E     IC                                                           1nos

::315Mhz Transmitter and receiver Module Pair       1nos

::9v dry battery                                                             2nos

::Copper clad board                                      50cm by 50cm

::Cardboard                                                   50cm by 50cm

::DC Motors                                                                 2nos

::Gears                                                                As requred

::Feviquick                                                                   10ml

::Ferric chloride                                                         30gms

::water in plastic bucket                                            

::Hand Drill

::Express Pcb software installed on your computer.

::Magazine paper

::Laser printer

Here is the block diagram of the remote control car --

The motor 1 is the steering motor and motor 2 is the engine power motor.I have used various stuff to design the hardware of the car and it will be discussed later. 

Now First of all Make the following circuit on Express pcb and then justify all the pin connection according to the given circuit diagram--

For making the pcb layout you must be familiar with express pcb software.It is the software used for designing the pcb layouts and it is freeware, you can download it from Here.It has two parts one is the Express SCH and other is Express PCB.The former is used to make the circuit diagram and then it is linked to the latter which is used for designing the pcb layout.If you don't want to make the circuit diagram in SCH then no matter you have to justify the layout in PCB design.

Now print the layout on a butter paper or a magazine paper with the help of laser printer.If you don't have a laser printer then most of the photo copy shop have the facility of laser printing then you must go there with the .xps file in flash drive and have the printed layout on butter paper or magazine paper.

Now you should cut the copper clad board with the help of a cutter of the size of layout and then cleane the copper side of the board with the help of scotch brite pad.Now further clean it with dry cloth and then put the printed side of paper on the copper side of board touching it. Now pre heat the cloth iron and then apply the heat and pressure to the board and paper using the iron for 10 minutes.You will observe after 10 minutes the paper has sticked to the board, now wash the board paper using water,you will see that the layout has transfered to the board and then dip it into the ferric chloride solution for 15 minutes. Now take out the board after 15 minutes and wash it using water.Now again wash it using thinner or kerosene oil, you will see that the pcb is ready to be drilled. Now using hand drill or stand still drill wit 1mm bit pierce the holes at appropriate places on the board for mounting the components.

Now according to the circuit diagram put appropriate components on their respective places and shoulder them using iron and paste and shoulder.Add the power supply and fix all the components pcbs and car hardware and your car is ready to use.

I have used the Lm7805, LD293D from Texas instruments and ST microelectronics.HT12E and HT12D from Holtek. 

For making the car hardware or chasis you must cut the appropriate size of the card board and the using the pads from telecoms companies which come with the SIM card, make all the support for the wheels and design the steering system as shown in fig. and then fit the motor and gears train to get more torque. And make all the connections,Your card is ready to run.

Here are some snapshots of car.