IC 555

The 555 timer IC is an integrated circuit  (chip) used in a variety of timer, pulse generation, and oscillator  applications. The 555 can be used to provide time delays, as an oscillator , and as a flip-flop element. Derivatives provide up to four timing circuits in one package.

Introduced in 1971 by American company Signetics, the 555 is still in widespread use due to its ease of use, low price, and stability. It is now made by many companies in the original bipolar and also in low-power CMOS types. 

PINS

Pin	Name	Purpose
1	GND	Ground reference voltage, low level (0 V)
2	TRIG	The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (hence TRIG is typically 1/3 VCC, CTRL being 2/3 VCC by default, if CTRL is left open).
3	OUT	This output is driven to approximately 1.7 V below +VCC or GND.
4	RESET	A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR.
5	CTRL	Provides "control" access to the internal voltage divider (by default, 2/3 VCC).
6	THR	The timing (OUT high) interval ends when the voltage at THR is greater than that at CTRL (2/3 VCC if CTRL is open).
7	DIS	Open collector output which may discharge a capacitor between intervals. In phase with output.
8	VCC	Positive supply voltage, which is usually between 3 and 15 V depending on the variation.

The connection of the pins for a DIP package is as follows:

Pin 5 is also sometimes called the CONTROL VOLTAGE pin. By applying a voltage to the CONTROL VOLTAGE input one can alter the timing characteristics of the device. In most applications, the CONTROL VOLTAGE input is not used. It is usual to connect a 10 nF capacitor between pin 5 and 0 V to prevent interference. The CONTROL VOLTAGE input can be used to build an astable multivibrator with a frequency modulated output.

Modes

The IC 555 has three operating modes:
Monostable mode:
 

A Monostable Circuit produces one pulse of a set length in response to a trigger input such as a push button. The output of the circuit stays in the low state until there is a trigger input, hence the name "monostable" meaning "one stable state". his type of circuit is ideal for use in a "push to operate" system for a model displayed at exhibitions. A visitor can push a button to start a model's mechanism moving, and the mechanism will automatically switch off after a set time. 

Astable (free-running) mode:

     

An Astable Circuit has no stable state - hence the name "astable". The output continually switches state between high and low without without any intervention from the user, called a 'square' wave. This type of circuit could be used to give a mechanism intermittent motion by switching a motor on and off at regular intervals. It can also be used to flash lamps and LEDs, and is useful as a 'clock' pulse for other digital ICs and circuits. 

Bistable
A Bistable Mode or what is sometimes called a Schmitt Trigger, has two stable states, high and low. Taking the Trigger input low makes the output of the circuit go into the high state. Taking the Reset input low makes the output of the circuit go into the low state. This type of circuit is ideal for use in an automated model railway system where the train is required to run back and forth over the same piece of track. A push button (or reed switch with a magnet on the underside of the train) would be placed at each end of the track so that when one is hit by the train, it will either trigger or reset the bistable. The output of the 555 would control a DPDT relay which would be wired as a reversing switch to reverse the direction of current to the track, thereby reversing the direction of the train. 

APPLICATION OF IC 555 ( CIRCUITS)

• 555 Amplifier
• Automatic Curtain Closer
• Bike Turning Signal
• Bi-Polar LED Driver
• Car Tachometer
• Clark Zapper
• Continuity Tester
• Dark Detector
• Driving A Bi-Coloured LED
• Driving A Relay
• Driving White LEDs
• Dummy Alarm
• Flashing Indicators
• Flashing LED
• Flashing Railroad Lights
• Hee Haw Siren
• Knight Rider
• 3x3x3 LED Cube

• Laser Ray Sound
• Latch
• LED Dice
• LED Dimmer
• Light Detector
• Machine Gun
• Metal Detector
• Metronome
• Model Railway Time
• Mosquito Repeller
• Motor PWM
• Music Box
• Police Lights
• Police Siren
• Rain Alarm
• Reaction Timer Game
• Roulette
• Screamer Siren - Light Controlled

• Servo Tester
• Siren 100dB
• Stepper Motor Controller
• Stun Gun
• Ticking Bomb
• Tilt Switch
• Touch Switch
• Toy Organ
• Traffic Lights
• Traffic Lights - 4 Way
• Transistor Tester
• TV Remote Control Jammer
• Uneven Clicks
• Up/Down Fading LED
• Wailing Siren
• Zener Diode Tester
• Servo Controller
• Voltage Doubler

RELAY ( SPDT-Single Pole, Double Throw )

Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate. They are often used to interface an electronic circuit (working at a low voltage) to an electrical circuit which works at very high voltage. For example, a relay can make a 5V DC battery circuit to switch a 230V AC mains circuit. Thus a small sensor circuit can drive, say, a fan or an electric bulb.

A relay switch can be divided into two parts: input and output. The input section has a coil which generates magnetic field when a small voltage from an electronic circuit is applied to it. This voltage is called the operating voltage. Commonly used relays are available in different configuration of operating voltages like 6V, 9V, 12V, 24V etc. The output section consists of contactors which connect or disconnect mechanically. In a basic relay there are three contactors: normally open (NO), normally closed (NC) and common (COM). At no input state, the COM is connected to NC. When the operating voltage is applied the relay coil gets energized and the COM changes contact to NO. Different relay configurations are available like SPST, SPDT, DPDT etc, which have different number of changeover contacts. By using proper combination of contactors, the electrical circuit can be switched on and off. 

HOW TO CONNECT A RELAY TO YOUR CIRCUIT

   In most of the cases you will have two output wires from your circuit that you are working on. Connect this two output wires to the two coil pins (pls refer the above diagram). Now connect the phase to the common pin if you need to work ac appliances or if you want to on another circuit that uses dc supply ,then connect the positive terminal of battery to the common pin.Now connect the phase(for ac) or positive(for dc) terminal to NO pin. connect neutral or ground directly to source.

HOPE THAT THE INFORMATION ABOUT RELAY WAS VERY USEFUL TO YOU..............

PLS NOTE THAT THE RELAY MODEL MAY VARY ACCORDING TO DIFFERENT MANUFACTURER..............BUT THE PINS  ARE ALL THE SAME AND WHAT DIFFER IS IT POSITION......................

DTMF DECODER CIRCUIT

DTMF (Dual Tone Multi Frequency) decoder circuit identifies the dial tone from the telephone line and decodes the key pressed on the remote telephone. Here for the detection of DTMF signalling, we are using the IC MT8870DE which is a touch tone decoder IC. It decodes the input DTMF to 5 digital outputs. The M-8870 DTMF (Dual Tone Multi Frequency)decoder IC uses a digital counting technique to determine the frequencies of the limited tones and to verify that they correspond to standard DTMF frequencies. The DTMF tone is a form of one way communication between the dialer and the telephone exchange. The whole communication consists of the touch tone initiator and the tone decoder or detector. The decoded bits can be interfaced to a computer or micro-controller for further application (For example, remote control of home /office electrical appliance using a telephone network, cell phone controlled home appliances, Mobile phone controlled robot, etc.)

In the early days, our phone system used to be operated by human operator in a telephone exchange room. The caller will pick up the phone, giving instruction to the operator to connect their line to the destination over the other end of the telephone. As more and more people find phone technology a useful communication tools, line connection use human operator has become a tedious task. 

As technology matures, pulse/dial tone method was inverted for telephony communication. It uses electronics and computer to assist in the phone line connection. Basically on the caller side, it is a dial tone generator. When a key is being pressed on the matrix keypad, it generate a unique tone consisting of two audible tone frequency. For example, if the key '1' is being press on the phone, the tone you hear is actually consist of a 697hz & 1209hz sine signal. Pressing key '9' will generate the tone form by 852hz & 1477hz. The frequency use in the dial tone system is of audible range suitable for transmission over the telephone cable. 


This project article focus on a simple DTMF (dual tone multi-frequency) decoder circuit. This circuit can be interface to a computer, allowing caller to computer interaction. Many communication application can be build for example, a computerize call receiving/diverting phone network system. Remote control to Home/Office electrical appliances using a telephone network. 

DTMF is a popular project especially in DSP (digital signal processing) subject. DSP software algorithm can be implement to generate as well as to decode DTMF tone. It is very interesting, and I will try to cover that aspect in near future. For now we do the hardware way. 

DTMF Circuits 

 Very small, roughly about my thumb size. 


Output Logic behavior from the DTMF decoder IC. 

no button press 

Q1: Logic 0 
Q2: Logic 0 
Q3: Logic 0 
Q4: Logic 0 

'1' press and hold 

Q1: Logic 0 
Q2: Logic 0 
Q3: Logic 0 
Q4: Logic 1 

release from button '1' 

Q1: Logic 0 
Q2: Logic 0 
Q3: Logic 0 
Q4: Logic 1 

'2' press and hold 

Q1: Logic 0 
Q2: Logic 0 
Q3: Logic 1 
Q4: Logic 0 

release from button '2' 

Q1: Logic 0 
Q2: Logic 0 
Q3: Logic 1 
Q4: Logic 0 

'0' press and hold 

Q1: Logic 1 
Q2: Logic 0 
Q3: Logic 1 
Q4: Logic 0 

Detection of dial tones is reflected on the bit TOE, while the output Q4, Q3, Q2, Q1 indicate the dial tone that is being detected on the telephony system. A complete table of the decoded digital output for individual dial tone is available in the coming section. 

Key Tone Output Logic 
Q1 Q2 Q3 Q4
1 0 0 0 1 
2 0 0 1 0 
3 0 0 1 1 
4 0 1 0 0 
5 0 1 0 1 
6 0 1 1 0 
7 0 1 1 1 
8 1 0 0 0 
9 1 0 0 1 
0 1 0 1 0 
* 1 0 1 1 
# 1 1 0 0 
A 1 1 0 1 
B 1 1 1 0 
C 1 1 1 1 
D 0 0 0 0 


These are the decoder output table for the given dial tone detected. Notice that there are key tone for A B C and D. These are special tone which are normally not found on our telephone. It is a common standard build into the decoder chip. 

The circuit is relatively simple and straight forward, and all components can be easily found

FOR MORE DETAILS WATCH THIS VEDIOS

https://www.youtube.com/watch?v=OF3SfGyvgbg

https://www.youtube.com/watch?v=c61ZU8NEs9o




TO BUY THE DTMF MODULE FOLLOW THE LINK GIVEN BELOW

http://www.amazon.in/Robomart-DTMF-Module-Version-3/dp/B00QUY4WAO/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1427033341&sr=1-1-catcorr&keywords=dtmf+module

http://www.amazon.in/DTMF-Module-MT8870-Decoder-Auxiliary/dp/B00RD55FNM/ref=pd_sim_sbs_t_1?ie=UTF8&refRID=09MTAMWT08NVY9XAE45E

http://www.robomart.com/index.php?route=product/search&filter_name=dtmf