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A remote control using HT12E and HT12D chips

2015-03-02 16:48  
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Abstract:-This is a remote control using HT12E and HT12D chips. HT12D & HT12E are widely used encoder/decoder chips in remote control applications made by "Holtek Semiconductors". 4 different channels can be utilized for different applications. Transmitter:-The figure given below shows schematic diagram of transmitter using IC HT12E (datasheet).HT12EConnections:- As shown in figure all the address lines A0-A7 are connected to ground. You can either connect all the lines to Vcc or to ground but keep in mind that on the receiver side you have to do same. This is to set same address both the sides. Resistor R1(1.1M?) is connected between oscillator pins (Osc1 & Osc2) to set transmitter frequency = 50×Receiver Frequency. Data lines D0-D3 are connected with switches S1-S4 through diodes D1-D4 respectively. The other terminal of all the switches is connected with ground. The TE pin (transmission enable) is also connected to all the switches through four different diodes D5-D8. The Dout pin is connected to one of i/p pin of AND gate IC 74LS09(datasheet). The second i/p of AND gate it tied to Vcc. The o/p of AND gate is connected with Reset i/p of IC-555 (datasheet). IC-555 is configured in astable multivibrator mode and it generates squarewave of 38 KHz continuously. The o/p of IC-555 drives two IR-LEDs and one red LED through transistor 2N2222A. Standard 9V battery is used as supply. Operation:-•Whenever you press any key TE pin will be grounded through that diode, at the same time particular data line is also grounded.•So we can set the data at the same time we can pull the TE pin low by pressing single key•Now we know when TE pin is low the address and data are transmitted serially through Dout pin.•The Dout pin controls the operation of IC-555 through AND gate. When there is 0 at output the operations of IC-555 is stopped and if 1 at output then IC-555 will generate burst of 38 KHz.•So Actually Address and Data are together modulated by 38 KHz carrier frequency.•Because the o/p of IC-555 is fed to IR-LEDs they will generate IR light beam of 38 KHzIf we press switch S1 then data word will be 1110 and address is of course 00000000. So the waveform will look like thisHT12EReceiver:-Receiver circuit using IC HT12D(datasheet) is as shown below.HT12EConnections:-All the address lines are connected to ground to set same address. Resistor R2 (51K?) is connected between Oscillator pins. All the data line D0-D3 are connected to different LEDs LED2-LED5 respectively through invertors IC 74LS04 (datasheet). LED1 is connected to VT (valid transmission) pin through transistor Q1 to indicate valid transmission. The output of IR sensor (datasheet) is connected to Din pin of chip HT12D. Operation:-•When 5V supply is given to circuit all the data lines are low. Because of invertors all four LEDs (LED2-LED5) will glow.•Whenever you press any switch from Tx address & data are transmitted together•IR sensor will demodulate the 38 KHz IR light beam and gives this address & data to IC HT12D•IC HT12D first compares the address three times and if it matches it gives high pulse on VT pin (so LED1 will blink) and latch the data.•Suppose you pressed 'S4'. So the data transmitted will be 1110 and address will be of course 00000000.•HT12D receives the signals compares address thrice, gives high pulse on pin VT and then latch the data. Because data is 1110 (because of invertors it would be 0001) LED2 will glow and rest all the LEDs will remain off•Same way if you press 'S2' data will be 1011. So now LED4 will be ON and rests are oFF.•Simply you can see which ever switch is pressed on Tx side that particular data line is low on Rx