10-01-2011, 04:23 PM
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Introduction
Earlier, we are looking into the face of future when we talked about automated devices, which could do anything on instigation of a controller, but today it has become a reality.
An automated device can replace good amount of human working force, moreover humans are more prone to errors and in intensive conditions the probability of error increases. Whereas an automated device can work with diligence, versatility and with almost zero error.
This is why this project looks into construction and implementation of a system involving hardware to control a variety of electrical and electronics instruments.
This circuit enables one to utilize a telephone for remote switching ‘on’ and ‘off’ of any electrically operated device.. The circuit is only acoustically coupled to the telephone instrument. Consequently, we do not have to pay a single extra paise to the telephone department except call charges. The switching operation is performed by making use of call + switch operations. While designing it has been ensured that the circuit is free from any false triggering by normal telephone ring signals.
With the help of this project, it is possible to control any electrical appliances from any distance.
In this project one base unit is connected to the basic landline in parallel with the existing telephone , but in the case of mobile phone we use handsfree enhancement kit option logic.. When we want to control any electrical appliances through outer phone then first we dial the home number, bell is ringing and after few bell phone is automatic on answering mode and ready for further operations . Now we press the eight digit excess code, one by one and if the excess code is ok then unit give a ack in the form of beep sound . Now we press the switch on/off code to on/off any electrical appliances. When we press a proper single digit number for on/off operation then connected unit is on/off. We use the phone keyboard for on/off the switches as per requirement. Total 10 operations are available. When the unit is on then circuit provide a reverse beep sound as an acknowledgement. This beep sound is different in on and off cases. In the on operation circuit feedback a two sound and in the off option circuit provide a single beep sound.
DTMF DECODER.
Our project is based on the dtmf signaling logic. When we press any digit from any phone then particular frequency is generated in the tone form. These frequencies are DTMF frequencies. We receive this frequency in the form of sound at the receiver phone. At the receiver end we decode this type of frequency with the help of handsfree enhancement setting option. In every phone there is an option of auto answer mode. In this mode phone is
automatically transferred into answering mode after few bells. When we press any key from transmitter then same key sound is available on the receiver end. We decode this sound with the help of the handsfree kit. Output of handsfree kit is further connected to the DTMF decoder circuit
In DTMF decoder circuit we use 8870 IC.This IC converts the DTMF tones in to corresponding binary outputs.
DTMF SIGNALLING. Ac register signaling is used in dtmf telephones, here tones rather than make/break pulse are used for dialing, each dialed digit is uniquely represented by a pair of sine waves tones. These tones (one from low group for row and another from high group fro column) are sent to the exchange when a digit is dialed by pressing the key, these tones lies within the speech band of 300 to 3400 Hz, and are chosen so as to minimize the possibility of any valid frequency pair existing in normal speech simultaneously. A valid dtmf signal is the sum of two tones, one from a lower group (697-940 Hz) and the other from a higher group ( 1209-1663 Hz). Each group contains four individual tones. This scheme allows 10 unique combinations. Ten of these codes represent digits 0 to 9. So no distortion is caused by harmonics. Each tone is sent as long as the key remains pressed. This significantly simplifies decoding because the composite dtmf signal may be separated with band pass filters into single frequency components, each of which may be handled individually.
CIRCUIT WORKING.
In this project our first part is DTMF decoder. DTMF ic receive the DTMF pulse and then converted into binary coded decimal. Pin no. 18 of the IC is connected to positive supply. In this circuit we use 5volt regulated power supply for the smooth working.
DTMF signal is applied to the pin no 2 and 3 of the IC through resistor and capacitor network. Capacitor of 0.1 microfarad work as a DC blocking capacitor. Pin no 5,6,9 are connected to the ground pin. Pin no 7 and 8 are connected to the 3.57945 MHz crystal. Pin no 16 and 17are connected to RC network work to provide a auto reset option, when the supply is on .
Binary output is available on the pin no 11,12,13,1,4, and this output is further connected to the Micro-controller 89C51.
Our next part of the circuit is IC 89C51. 89C51 is 40 pin IC. Pin no 40 of the IC is connected to the 5volt positive supply. Pin no 40 and pin no 31 both are connected to the positive power supply. Pin no 20 of the IC is connected to the common ground pin. Pin no 9 is a reset pin. One capacitor and resistor network is connected to pin no 9. In this IC total 4 ports are available. So total 32 pins are available for input and output
Output from the DTMF decoder is connected to microcontroller and as well as connected to the password section. Output from the Decoder is connected in parallel to the controller and as well as IC 74154. Here IC 74154 converts the bcd signal into decimal signal.
So signal from the decoder is first pass by the password section and when password section pass the password then password section provide a signal to the controller.
In this section we use two IC one is 74154 and second is IC 4017 . Both IC generate a combination of sequence by which we enable the micro-controller.
When we want to switch on the base unit by outer phone then phone is automatic on after few bells, this is achieved by another circuit. But after few bells when phone is on and unit require a code of 8 DIGITS numbers. When we press a proper code, then only micrcontroller allow us to switch on the circuit.
First IC of this section is IC 74154. IC 74154 is a bcd to decimal decoder. 74154 is active low IC. Pin no 20,21,22,23 is connected to dtmf decoder IC.
Pin no 18 and 19 of this IC is connected to the collector of one NPN transistor base of the NPN transistor is connected to the pin no 15 of the IC 8870. When DTMF decoder decodes the signal at that time pin no 15 is on for a time and acknowledge the signal. This signal is fed to the base of NPN transistor through 1 k ohm resistor. When this signal is coming then 74154 is on and gives an output. Pin no 18 and 19 of the 74154 is the enable pin of the IC. On this pin we provide an active low signal for activation.
If we press the proper code in steps then at every digit of code 74154 is on and gives the corresponding output as per the digit. Output of the IC 74154 is connected to the PNP transistor base point through 10 k ohm resistor. Emitter of the all PNP transistor is connected output of the decade counter circuit. Here we use IC 4017 as a decade counter circuit. Pin no 16 is the positive supply pin and pin no 8 is the negative pin. Pin no 14 of the IC is clock input of the IC. On starting mode when it is in on reset mode then it start from the zero point. Zero means first output is available on the pin no 3. Its means pin no 3 is positive in first output. Now IC 4017 receive a clock pulse on pin no 14 then counter shifts its output from pin no 3 to next output on pin no 1 , pin no 2.
As we press the proper code then IC 74154 gives an output and this output is available on the output pin, with the help of this output PNP transistor is on and positive output is available on the collector point of the PNP transistor. All the PNP transistor collector point is connected together is and reconnected to the clock input of the ic 4017 through RC network to another NPN transistor. By this NPN transistor we give a clock pulse to the pin no 14 of the IC 4017. As the counter moves after incoming clock pulse then last output is available on the pin no 9. As the last output is available on pin no 9. After getting a voltage on the pin no 9 we switch on the next pair of NPN transistor. Output of first NPN transistor on collector is connected to the port p3.4 to give a acknowledge signal that code lock is loaded successfully. Output of the this NPN transistor is again connected to the base of next NPN transistor. Collector of this NPN transistor disable the pin no 18 of the IC to receive any further code input of the signal
Output of IC 4017 ( with transistor circuit) not only provide a password ok signal to the controller but at the same time switch off the IC 74154 to get another signal for password.
Once the password section is off then Microcontroller gets a signal and provide a sound feedback in five beeps.
After getting a beep sound from the controller dialer person press a single digit a key for the operation. As we press the single digit key, controller gets a signal from dtmf decoder and further microcontroller on/off the corresponding output . All the outputs are connected to the port P0 and P2. On these output we connect 8 different LEDs. As we press the digit code output LED is on and remain on until we press the same code again. Output is work as a toggle switch.
LED output of the microcontroller is further connected to the triac circuit through opto-coupler circuit. Output from the microcontroller is firstly connected to the optocoupler pin no 1. This optocoupler is a special interface device to interface the controller with the triac circuit.
The MOC3121( optocoupler) is optically isolated triac driver devices. These devices contain an infra red emitting diode and a light activated silicon bilateral switch. They are specially designed for interfacing between electronics controls and power triac to control resistive and inductive loads for 240 volt Ac operation.
Pin no 1 is anode pin of infra red transmitter.
Pin no2 is cathode pin of infra red transmitte.r
Pin no 4 and 6 is the output pin.
Pin no 6 is output pin and connected to the gate of the triac through 100 ohm resistor.
At the output of the triac we control any 220 load. In this project its our choice, how many optocoupler we interface this circuit. If we use 10 opto- coupler then we interface 10 load output with this circuit.
Now when IC recieve any pulse then output led is on and then load is on. Again we press the same code then led is off and load is also off.
(CODING AND DIAGRAMS ARE IN THE ATTACHED FILE)
