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1) CPD is defined as the value of the IC’s internal equivalent capacitance which is calculated from the operating current consumption without load. (Refer to Test . Integrated Circuit. Transistor Transistor Logic (TTL). 4−Line−to−16−Line Decoder /Demultiplexer. 24−Lead DIP Type Package. Description: The NTE is a. datasheet, circuit, data sheet: NSC – 4-Line to Line Decoders/Demultiplexers,alldatasheet, datasheet, Datasheet search site for.

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Some technologies like IR remote control are used for short distance applications. In such case if we have system which does not require any radiations or which is not harmful, long remote control switch!! Yes here is the solution. Here I am using a telephone as a media, which serves main part of this system, by using home phone as a local phone and another phone, either landline or mobile phone as a remote phone.

You can control up to 10 devices. It may dataxheet any electric or electronic appliances or devices with simple to heavy appliances. Each device is given a unique code.

It makes accurate switching, any false switching of device are not done.

There is no risk for false switching. Your local phone i. So you need not use a separate telephone line for this device controlling.

To perform any operations through remote phone line, the user needs to dial to the local telephone to which the interfacing circuit is connected then the respective code of the device is dialed. This circuit does not require any complex IC, so any one with little knowledge of electronics can construct this circuit, because it does not need any programmable IC’s or programming. This system detects the ringing signal from your exchange with the help of ring detector and automatically switches ON.

This device saves your money. This circuit switches OFF after a time of 60 seconds you can change this switch ON-Time which is discussed in detail in coming section. Before changing the state of the device we can confirm the present status of the device. This circuit gives an acknowledgement tone after switching ON the devices to confirm the status of the device.

You can control devices from local telephone. It can also be controlled by PCO. Taking a tour of the project: We have two type of dialing facilities in our telephone system i Pulse dialing mode ii Tone dialing mode.

Here this system works on tone dialing mode. The DTMF mode is shortly called as tone dialing mode. Check for availability of tone dialing mode in your telephone set.

This system is divided into two sections 1: It is nothing but remote telephone set which is present in the remote place. Signals are sent through this telephone.

This is a control system through which you can control your appliances.

This contains one telephone line and a control unit. The appliances to be controlled must be connected to telephone line through control unit. Control unit is kept with a sufficient backup. When you press a button in the telephone set keypad, a connection is made that generates a resultant signal of two tones at the same time.


These two tones are taken from a row frequency and a vatasheet frequency. The resultant frequency signal is called ” Dual Tone Multiple Frequency “. These tones are identical and unique. A DTMF signal is the algebraic sum of two different audio frequencies, and can be expressed as follows: Where f a and f b are two different audio frequencies with A and B as their peak amplitudes and f as the resultant DTMF signal.

Each of the low and high frequency groups comprise four frequencies from the various keys present on the telephone keypad; two different frequencies, one from the high frequency group and another from the low frequency group are used to produce a DTMF signal to represent the pressed key. The amplitudes of the two daatasheet waves should be such that.

The frequencies are chosen such that they are not the harmonics of each other. The frequencies associated with various keys on the keypad are shown in figure A. The row and column frequencies are given below: When you press the digit 5 in the keypad it generates a resultant tone signal which is made up of frequencies Hz and Hz.

Pressing digit 8 will produce the tone taken from tones Hz and Hz. In both the cases, the column frequency Hz is the same. These signals are digital signals which are symmetrical with the sinusoidal wave. A Typical frequency is shown in the figure below: Along with these DTMF generator in our telephone set provides datashert set of special purpose daatsheet of tones, which is normally not used in our keypad.

These tones are identified as ‘A’, ‘B’, ‘C’, ‘D’. These frequencies have the same column frequency but uses row frequencies given in the table in figure A.

These tones are used for communication signaling. The frequency table is as follows: Due to its accuracy and uniqueness, these DTMF signals are used in controlling systems using telephones. This system is divided into two sections, 1: This unit consists of telephone set which is present in the remote place.

(PDF) 74154 Datasheet download

By pressing any key in the keyboard corresponding DTMF signal is available in its output pin at pin no. For producing the appropriate signals it is necessary that a crystal oscillator of 3. Circuit diagram of the DTMF encoder. This encoder IC requires a voltage of 3V. For datawheet IC is wired around 4. And 3V backup Vcc for this IC is supplied by using 3. The row and column frequency of this IC is as on the fig.

National Semiconductor

By pressing the number 5 in the key pad the output tone is produced which is the resultant of addition of two frequencies, at pin no. This signal is sent to the local control system through telephone line via exchange. This is a control unit through which you can control your appliances. This contains one telephone line and a Local Control Section. Before going into detail of the circuit, we will take a brief description about integrated circuits used in local control section.

It uses same oscillator frequency used in the remote section so same crystal oscillator with frequency of 3. Its filter section uses switched capacitor technology for both the high and low group filters and for dial tone rejection.


Its decoder uses catasheet counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. Minimal external components required include a low-cost 3. The MT can also inhibit the decoding of fourth column digits. The low and high group tones are separated by applying the dual-tone signal to the inputs of two 6 th order switched capacitor band pass filters with bandwidths that correspond to the bands enclosing the low and high group tones.

The filter also incorporates notches at and Hz, providing excellent dial tone rejection. Each filter output is followed by a single-order switched capacitor section that smoothes the datashert prior to limiting.

Signal limiting is performed by high gain comparators provided with hysteresis to prevent detection of unwanted low-level signals and noise. The MT decoder uses a digital counting technique to determine the frequencies of the limited tones and to verify that they correspond to standard DTMF frequencies. When the detector recognizes the simultaneous presence of two valid tones known as signal conditionit raises the Early Steering flag ESt.

Any subsequent loss of signal condition will cause ESt to fall. Before a decoded tone pair is registered, the receiver checks for valid signal duration referred to as character- recognition-condition. This check is performed by an external RC time constant driven by ESt. The contents of the output latch are made available on the 4-bit output bus by raising the three state control input OE to logic high.

Inhibit mode is enabled by a logic high input to pin 5 INH. It inhibits the detection of Hz. The output code will remain the same as the previous detected code. On the M- models, this pin is tied to ground logic low. The input arrangement of the MT provides a differential input operational amplifier as well as a bias source VREF to bias the inputs at mid-rail.

Provision is made for connection of a feedback resistor to the op-amp output GS for gain adjustment. The internal clock circuit is completed with the addition of a standard 3.

IC NE timer: This IC is used as a multivibrater click here to download datasheet.

Datasheet, PDF – Alldatasheet

By using this IC we can construct two types of multivibrater, monostable and astable. The monostable multivibrater produces a single pulse when dahasheet triggering pulse is applied to its triggering input.

The astable multivibrater produces a train of pulses depending on the Resister-Capacitor combination wired around it. With a monostable operation, if time delay is controlled by one external resistor and one capacitor datsheet between Vcc-Discharge Rand Threshold-Ground C.

With an astable operation, the frequency and pulse width are produced by two external resistors and one capacitor connected between Vcc-Discharge RDischarge-Threshold Rand Threshold-Ground C. IC is a line decoder, it takes the 4 line BCD input and selects respective output one among the 16 output lines click here to download datasheet.

It is active low output IC so when any output line is selected it is indicated by active low signal, rest of the output lines will remain active high.