555 Timer IC Working Principal
Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high output from the flip-flop saturates the discharge transistor and discharge the capacitor connected externally to pin 7. The complementary signal out of the flip-flop goes to pin 3, the output. The output available at pin 3 is low. These conditions will prevail until comparator 2 triggers the flip-flop. Even if the voltage at the threshold input falls below 2/3 VCC, that is comparator 1 cannot cause the flip-flop to change again. It means that the comparator 1 can only force the flip-flop’s output high.
To change the output of flip-flop to low, the voltage at the trigger input must fall below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its output low. The low output from the flip-flop turns the discharge transistor off and forces the power amplifier to output a high. These conditions will continue independent of the voltage on the trigger input. Comparator 2 can only cause the flip-flop to output low.
From the above discussion it is concluded that for the having low output from the timer 555, the voltage on the threshold input must exceed the control voltage or + 2/3 VCC. They also turn the discharge transistor on. To force the output from the timer high, the voltage on the trigger input must drop below +1/3 VCC. This also turns the discharge transistor off.
A voltage may be applied to the control input to change the levels at which the switching occurs. When not in use, a 0.01 nano Farad capacitor should be connected between pin 5 and ground to prevent noise coupled onto this pin from causing false triggering.
Connecting the reset (pin 4) to a logic low will place a high on the output of flip-flop. The discharge transistor will go on and the power amplifier will output a low. This condition will continue until reset is taken high. This allows synchronization or resetting of the circuit’s operation. When not in use, reset should be tied to +VCC.
About the NE555 Timer
The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. With just a few external components it can be used to build many circuits, not all of them involve timing! A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.
Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555.
The circuit symbol for a 555 (and 556) is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labelled with their function.
The 555 and 556 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum). Standard 555 timer and 556 ICs create a significant 'glitch' on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor (eg 100µF) should be connected across the +Vs and 0V supply near the 555 or 556.
The 555 has three operating modes:
- Monostable mode: in this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc.
- Astable - free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.
- Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bouncefree latched switches, etc.
NE555 Circuit Schematic
555 Timer IC Photo
555 Timer Models and Manufacturers
Project: Ignition Coil Driver with 2N3055 and 555 Timer
Here is a very simple circuit that will provide high voltage (15-40kV) sparks using a common ignition coil. The input is 12VDC at around 5 to 6 amps. Mine produces sparks that are about 3/4" to 1" in length. A 2N3055 NPN power transistor is pulsed with a square wave signal that comes from the 555 timer IC. The frequency of the pulses depends on the resistors between pins 7 and 8 and between pins 7 and 6. The pulse is also dependent on the capacitor. You can experiment with these values. Try inserting a smaller capacitor to raise the frequency. At different frequencies the sparks will change certain characteristics. At a high frequency the sparks will get fatter but shorter in length. At lower frequencies the spark maybe longer but thinner. I assembled my project on a solderless breadboard. You can use whatever you like. The capacitor should be a tantalum or mylar type, but this is not absolutely necessary. A ceramic type should work fine just as long as the temperature is not too high around it. Read more: http://www.geocities.com/CapeCanaveral/Lab/5322/coildrv.htm
Project: Using the NE555 in a Magnetically Operated Gun
The circuit is designed to produce a gun using the technology of magnet to drive a minimal hit a long distance horizontally or a few distance vertically. A magnet is an element that creates magnetic field which is a force that pulls on ferromagnetic materials and attracts or repel other magnets. It is created by moving charges such as electric current. It can also be created by the spin magnetic dipole moment, and by the orbital magnetic dipole moment of an electron within an atom.
The operation of the circuit starts with the 555 timer acting as oscillator being operated in astable mode where it performs pulse generation at a rate of 10 ms to the IC2 (4017B). The pin 15 will continue to take low at the fire button, while 4017B keeps on resetting. The outputs of Q1 to Q7 are sequenced by IC2 to provide power to TR1 to TR4 transistors. This in turn will launch in rapid sequence the inductors L1 to L4. The transformer can produce a 25.5 V DC to the electromagnets when rectified and leveled. The winding of the electromagnets on the copper tube will be cut in two after 500 turns. To slide one on the copper tube, the winding should be at the base of reversed sellotape. The physical size of the galvanized wire bullet is 2 mm diameter and 3 cm long. It should freely glide inside the copper tube.
Caution should be observed in positioning the electromagnets L1 to L4 on the copper tube to obtain optimum effectiveness on the movement of the bullet and arranging the voltage across resistor R1.
There are two basic types of electromagnetic gun, the rail gun and the coil gun. Both used stored energy to produce large magnetic field and high electric current through a driving armature. The interaction of the current with the magnetic field generates a force which propels the armature and any projectile connected to it.
555 Timer IC History: An Interview with Inventor Hans Camenzind
This Oral History is excerpted from an interview conducted in June, 2004.
In addition, reference is made to an article by Hans Camenzind, “Redesigning the old 555”, IEEE Spectrum, Sept 1997.
Hans, let’s start the Oral History with your recollections of the initial success of the 555 integrated circuit.
That 555 family was a total surprise. I wanted to make it flexible, that was the whole purpose, but I didn’t realize it was so flexible. There are applications now that still sound crazy to me. And the quantity! In the second year it moved to the largest quantity sold of any IC and it has stayed that way for 30 years. The original application was as a timer and oscillator, but it has moved well beyond that.
According to the IEEE Spectrum article you wrote on the 555, there was reluctance at Signetics to invest in this product. Is that right?
The engineering department at Signetics - yes, they were a bit stodgy for a semiconductor company. They were at the forefront. They had tried everything. It was a surprising reaction, and it was simply a reflection of the turf. You know, they were designing and making operational amplifiers.
Was that their primary business?
Yes, the primary linear business, although I think the digital portion (RTL and DTL) was still much larger. For the linear, op amp was king. So they figured that if I designed a circuit that replaced one or two op amps, that would cut into their sales.
How did the 555 name come about?
Signetics had “500” numbers, and the earlier product I worked on was the 565, 566 and 567. It was just arbitrarily chosen. It was Art Fury (Marketing Manager) who thought the circuit was gonna sell big who picked the name “555”.
I wonder how many of these have been made?
At the moment, it is about 1 billion devices a year. These are mostly made in Korea now, Samsung. The electronics industry is big now.
Are there other chips with this kind of popularity?
You could say that the op amp is bigger, but there are so many different op amps, they have to specialize – there is no perfect op amp, so you optimize it, for different parameters. There must be 500 different op amp types.
555 Timer IC Datasheets and Related Keywords
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