How a 555 Timer IC Works NE555 Tutorial

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The 555 timer IC is an integrated circuit used in a variety of timer, pulse generation, and oscillator applications. • The integrated NE555 performs the timer function thanks to an external RC network. Internally it has two comparators and a flip flop, as well as an integrated resistive divider, which make it an excellent circuit to make timers, oscillators and many circuits. • The name derives from the internal resistive divider, consisting of three 5Kohm resistors. • It is one of the most economical integrated on the market, the first versions were transistor, the most modern versions are in cmos technology. • Introduced in 1972 by Signetics, the 555 is still in widespread use due to its low price, ease of use, and stability. It is now made by many companies in the original bipolar and in low-power CMOS technologies. • As of 2003, it was estimated that 1 billion units were manufactured every year. The 555 is the most popular integrated circuit ever manufactured. The integrated device can work in three modes: Astable, Monostable and Bistable Mode. • Astable 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. • 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. • Bistable Mode (or Schmitt Trigger) • 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. • ► Pin Configuration: • Pin 1 (Ground): • Connects to the 0v power supply. • Pin 2 (Trigger): • Detects 1/3 of rail voltage to make output HIGH. Pin 2 has control over pin 6. If pin 2 is LOW, and pin 6 LOW, output goes and stays HIGH. If pin 6 HIGH, and pin 2 goes LOW, output goes LOW while pin 2 LOW. This pin has a very high impedance (about 10M) and will trigger with about 1uA. • Pin 3 (Output): • (Pins 3 and 7 are in phase. ) Goes HIGH (about 2v less than rail) and LOW (about 0.5v less than 0v) and will deliver up to 200mA. • Pin 4 (Reset): • Internally connected HIGH via 100k. Must be taken below 0.8v to reset the chip. • Pin 5 (Control): • A voltage applied to this pin will vary the timing of the RC network (quite considerably). • Pin 6 (Threshold): • Detects 2/3 of rail voltage to make output LOW only if pin 2 is HIGH. This pin has a very high impedance (about 10M) and will trigger with about 0.2uA. • Pin 7 (Discharge): • Goes LOW when pin 6 detects 2/3 rail voltage but pin 2 must be HIGH. If pin 2 is HIGH, pin 6 can be HIGH or LOW and pin 7 remains LOW. Goes OPEN (HIGH) and stays HIGH when pin 2 detects 1/3 rail voltage (even as a LOW pulse) when pin 6 is LOW. (Pins 7 and 3 are in phase. ) Pin 7 is equal to pin 3 but • pin 7 does not go high - it goes OPEN. But it goes LOW and will sink about 200mA. • Pin 8 (Supply): • Connects to the positive power supply (Vs). This can be any voltage between 4.5V and 15V DC, but is commonly 5V DC when working with digital ICs. • Music by Vexento • ► More videos: / stefano91ste • WARNING: This video is only for demonstration. I don't take any responsibility for damage to things, people and animals. • ► My equipment: • Panasonic HC-V180 (Main Camera) • iPhone 6 (Secondary Camera) #ElectronicProjects #Electronic

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