Cheapest way of Controlling Home appliances using RF Transmitter receiver

Hi Everybody, Welcome to Paperelectronics

This post deals with how to make simple RF Transmitter and Receiver to control Home Appliances,


Things Required,

• HT12E
• HT12D
• RELAY
• GENERAL PURPOSE BOARD (OR CLAD BOARD ,if you want your circuit attractive)
• RF Transmitter and Receiver
• BC547 Transitter 
• SOLDERING GUN+ LEAD

Before going into the experiment we should have knowledge about Encoder and Decoder IC

 (ref datasheet)
I will give important points that you have to keep in mind while designing (if u are lazy),

HT12E

DATA and ADDRESS PINS:
----It has 4 Data bits and 8 address bits
(by this you can send 4 data bits(For HT12E) at a time, address bit contains the address of the receiver to which it is transmitted )
These pins can be externally set to GND(LOGIC 0) or left open (LOGIC 1)

By default the address pins are high (i.e)logic 1 if you want to give logic 0 then ground respective pins

Reality example: if you want to send data to decoder with address 10101010 ,then leave A0,A2,A4,A6 (BY DEFAULT OPEN PINS TAKE LOGIC 1) and Ground (A1,A3,A5,A7)

LIKEWISE FOR DATA PINS ,IF YOU WANT TO SEND DATA 1001 (THEN GROUND THE RESPECTIVE PINS)

TRANSMISSION ENABLE:

After setting data ,you should acknowledge the Encoder that data is ready for transmission and transmit the data ,the is done by Transmission Enable pin ,which is active low (it should be grounded to transmit data (permanent grounding can also be done, but power loss will be there)

OSCILLATOR PINS:
The oscillator Resistor is connected here which generates pulse for encoding (RC OSCILLATOR-Just Google it)

DATA OUT:
The 4 data bits will be encoded serially and the output serial data is given out through Dout pin, this pin is connected to RF transmitter  input.

Reality example:
     BIT1 +DELAY+BIT2+DELAY+BIT3+DELAY+BIT4
Lets say Data is 1001
1 delay 0 delay 0 delay 1 -----------will be the output of encoder DOUT

Oscillator is Responsible for this delay (frequency of pulse can be varied by varying resistor Ref:datasheet)

VDD & VSS:  (ref diagram)


RF Transmitter:

Dout of the Encoder is connected to DATA pin of the RF transmitter
Vcc  is given 5V
Ant is the Antenna pin (the coverage area can be increased by connecting an antenna to this pin)

HT12D:
DATA and ADDRESS PINS:
----It has 4 Data bits and 8 address bits
Address pins is used to set the address of the decoder (just refer HT12E ,to know how to set the address) Remember both address should be same (better leave address pins open for both HT12D and HT12E, default adress 11111111 will be set)

DIN:
The output which transmitted through RF transmitter ,is received through RF receiver ,the input is fed to DIN Pin of the Decoder,

OSCILATOR PINS:
The oscillator Resistor is connected between these pins which is responsible for generation of Decoder Frequency

VT:
Valid transmission pin acknowledges us by giving a high pulse ,if the received data address matches with the address which is set in DECODER IC

Reality example: you can connect a LED in Vt pin through BC547(transistor ) to know whether valid data has come (confused! follow the post)


Resistor selection:

THIS Section is important for oscillator frequency generation

The recommended oscillator frequency is fOSCD (decoder) =50 fOSCE (HT12E encoder)

(Refer graph below to set the encoder and decoder oscillator frequency)

Graph for Encoder Frequency setting

I am setting encoder ferquency as 3 Khz  ,by connecting 1.1 Mohm (or 1 Mega ohm) between oscillator Pins of Encoder (as i use 5 volt supply and want to generate 3 Khz ,(plot graph according to your voltage source and available resistor )

Graph for Decoder Frequency setting:

I have set Encoder Frequency as 3 Khz ,so Decoder frequency should be 50(3Khz) (i.e) 150Khz
as
The recommended oscillator frequency is fOSCD (decoder) =50 fOSCE (HT12E encoder)
(ref datasheet, this formula is applicable for only HT12 Encoder and HT12 decoder ICs)

Now plot graph between 5V and 150  Khz in the graph you will get 51 Kilo ohms
(i am using 47Kohm as 51k is not available, use nearby value)

RF Receiver

Kindly Short Pin 1,6,7 to Gnd and  4,5 to say 5 V .

            Pin 3 - Leave open                             

Pin 2 - to 14th Pin of HT12D

Pin 8 - Connect to an antenna for long range / leave open for short range

BC 547 Transistor:

what is the Need For Transistor?

   The O/P Power from Decoder is Not Sufficient to Drive a Relay , So We are Using Transistor to Increase the Drive Power.

How?

Say For Eg : I want to Control  12 Volt motor Based on 5 Volt O/p from Sensor ,

Circuit Would Be,

It is a NPN Transistor, which works in 4 modes (Active,Saturation Cut-off, Reverse Active)

Here we will using Transistor only as Switch (Active(ON-state) and Cut-off( Off-state))

 If The Sensor Detects any Obstacle ,It Gives 5 Volt O/p (Blue Highlighted) ,which Drives The  Transistor (Goes to Active Mode (i.e ) Emitter collector Shorts,Now the Motor  Rotates

If there is no obstacle , the Transistor is in Off State , Motor Remains off.

(Thus we ran 12 Volt motor from 5 Volt Sensor O/p using Transistor.



IR Receiver circuit: