GROUP MEMBERS:- PRITAM,BHAVESH,VRAJ SUBMITTED TO:- HITENDRA JOSHI

555 TIMER 555 timer is an integrated circuit that very stable. Use as monostable multivibrator, astable multivibrator, analog square wave signal generator, achometer frequency meter and others. Basically, 555 timer operate in 2 mode, ◦ Monostable ◦ Astable

FUNCTION OF EACH PIN TIMER REFER TO MONOSTABLE MULTIVIBRATOR PIN 1 : GROUND -all the measure voltage must refer to this pin PIN 2 : TRIGGER - It is used to set the flip-flop. - Output is LOW if voltage at pin > 2/3 Vcc - When negative trigger pulse is 1/3 Vcc, output at comparator 2 cause the timer output HIGH. PIN 3 : OUTPUT - Output can connect at 2 output pin, pin 3 and pin 1 or pin 3 and pin 8. - When output LOW, current will flow through load that connected between pin 3 and pin 8 to output terminal, know as SINK CURRENT. - Current flow through load that connected between pin 3 and pin 1, known as SOURCE CURRENT. - Maximum current for source current and sink current is 200mA.

CONTINUE….. PIN 4 : RESET - Reset with negative pulse - When the reset pin is not used, the pin is connected to +Vs to avoid false trigger. PIN 5 : CONTROL VOLTAGE - Normally is connected to earth through 0.01µF capacitor - If output voltage is connected to pin 5, the output waveform bandwidth can be changed µF capacitor can avoid from noise problem. PIN 6 : THRESHOLD VOLTAGE - Input for inverting pin at comparator 1 - When voltage at this pin ≥2/3 Vcc, output at comparator 1 is HIGH, output timer LOW. PIN 7 : DISCHARGE - This pin is connected internally to collector at transistor Q1. - When output HIGH, Q1 OFF, circuit open - When output LOW, Q1 saturated capacitor C discharge through Q1. PIN 8 : SUPPLY VOLTAGE, Vcc - +5 V to 18V

555 TIMER INTEGRAL CIRCUIT

A view inside the 555 IC / Black Box

MONOSTABLE MULTIVIBRATOR Known as shoot multivibrator Pulse generator circuit which the period is calculated from RC network and connected to external of 555 timer Stable when the output logic LOW (logic = 0) When a pulse is trigger at pin 2 (normally negative trigger pulse), timer output will change to HIGH (+Vs) for a while and change to LOW (stable condition). The condition will continue LOW until pulse is trigger again. The timing period is triggered (started) when trigger input (555 pin 2) is less than 1/3 Vs, this makes the output high (+Vs) and the capacitor C1 starts to charge through resistor R1. Once the time period has started further trigger pulses are ignored. The threshold input (555 pin 6) monitors the voltage across C1 and when this reaches 2/3 Vs the time period over and the output becomes LOW, At the same time discharge (555 pin 7) is connected to 0V, discharging the capacitor ready for the next trigger.

CONTINUE…. CONNECTION FOR MONOSTABLE MULTIVIBRATOR

CONTINUE…. Operation for monostable multivibrator : ¤ Assume initial output is LOW, circuit at stable condition, transistor Q1 ON, capacitor is connected to ground. ¤ When negative pulse is triggered to PIN 2, transistor Q1 OFF (Q1 open circuit), capacitor C start charging through resistor R1 and output is HIGH. ¤ When voltage at capacitor, C reach 2/3 Vs, output will change to LOW through flip flop. At the same time, flip flop output will make the Q1 ON. Capacitor will discharge through transistor Q1. ¤ Monostable output will remain LOW until another trigger pulse is triggered to pin 2.

ASTABLE MULTIVIBRATOR CONNECTION FOR CONNECTION FOR ASTABLE MULTIVIBRATOR

CONTINUE… Known as free running multivibrator. Do not have stable condition, the condition always change. Astable do not need trigger pulse for external to change the output. The period for LOW and HIGH can be calculated based on resistor and capacitor value that connected at outside of timer. Operation for astable multivibrator : i) Assume the initial is HIGH. Transistor Q1 OFF and capacitor is charging through resistor R A and R B. ii) When capacitor voltage reach 2/3 Vee, Comparator 1 will trigger flip flop and output change from change from HIGH to LOW. Resistor R B and transistor Q1. iii) When the capacitor voltage reach 1/3 Vee, comparator output 2 will trigger flip flop so the timer output is HIGH. The cycle is repeated. Period for capacitor charging from 1/3 Vcc to 2/3 Vcc same as period for HIGH output at timer. Period for capacitor discharging from 2/3Vcc to 1/3 Vcc same as period for LOW output at timer.

FORMULA FOR TIMER T H = (R A +R B ) C T L = (R B ) C Period, T = T H + T L = (R A + 2R B ) C Frequency, f = 1/T = 1/ (T H + T L ) = 1.44 / ((R A + 2R B ) C) % Duty Cycle = [T H / (T H + T L ) ]x 100 = [(R A + R B ) / (R A + 2R B )] x100

555/556 Inverting Buffer (Schmitt trigger) or NOT gate The buffer circuit's input has a very high impedance (about 1M Ω ) so it requires only a few µA, but the output can sink or source up to 200mA. This enables a high impedance signal source (such as an LDR) to switch a low impedance output transducer (such as a lamp). It is an inverting buffer or NOT gate because the output logic state (low/high) is the inverse of the input state: NOT gate - Input low (< 1 / 3 Vs) makes output high, +Vs - Input high (> 2 / 3 Vs) makes output low, 0V 555 inverting buffer or NOT gate NOT gate symbol

CONTINUE… When the input voltage is between 1 / 3 and 2 / 3 Vs the output remains in its present state. This intermediate input region is a deadspace where there is no response, a property called hysteresis, it is like backlash in a mechanical linkage. This type of circuit is called a Schmitt trigger. If high sensitivity is required the hysteresis is a problem, but in many circuits it is a helpful property. It gives the input a high immunity to noise because once the circuit output has switched high or low the input must change back by at least 1 / 3 Vs to make the output switch back.

555/556 Bistable (flip-flop) - a memory circuit The circuit is called a bistable because it is stable in two states: output high and output low. It is also known as a 'flip-flop'. It has two inputs: Trigger (555 pin 2) makes the output high. Trigger is 'active low', it functions when < 1 / 3 Vs. Reset (555 pin 4) makes the output low. Reset is 'active low', it resets when < 0.7V. The power-on reset, power-on trigger and edge-triggering circuits can all be used as described above for the monostable.monostable

Bistable Multivibrator

THEORY OF OPERATION Because R3 and R4 creates a voltage that is exactly in the middle of the dead zone of the Schmitt Trigger hysteresis the output of the 555 is stable. It will hold the last state it was set in indefinitely while there is power. The capacitor C1 is at the same voltage as the output of the timer. When the toggle button is pushed the capacitor will put the same voltage on the input, causing the 555 (an inverter), to flip states. The capacitor will quickly charge or discharge to the voltage level that the network of R3, R4, R5 now presents. Since R5 is X10 larger than R3 and R4 this voltage will still be in the dead zone of the Schmitt Trigger and the output of the 555 is stable in its new state. When the toggle button is released the capacitor will again charge or discharge to its new voltage. The capacitor is being used as a memory to compliment the 555. It also makes a fairly convenient debounce for the button. This circuit concept will work for all inverting Schmitt Triggers, though R5 may have to be increased to keep the transitions in the dead zone of the hysteresis.

Typical Project applications for a 555 IC: - Monostable: Astable: Aroma Fan Shaky Hand Game Bicycle Hazard Lights Bicycle Indicators Egg Timer, Telephone Timer, Game / Chess Timer etc. Burglar Alarm Electronic Dice Sensitive Touch Switch A Child’s mini electric organ Simple Siren Bleeper circuit Random Number Generator etc, etc..

Dark Detector: It will sound an alarm if it gets too dark. For example, this circuit could be used to notify when a lamp (or bulb) burns out. The detector used is a regular cadmium-sulphide Light Dependent Resistor or LDR, for short, to sense the absence of light and to operate a small speaker. The LDR enables the alarm when light falls below a certain level

Tilt Switch: Actually really a alarm circuit, it shows how to use a 555 timer and a small glass-encapsulated mercury switch to indicate 'tilt'. The switch is mounted in its normal 'open' position, which allows the timer output to stay low, as established by C1 on start-up. When S1 is disturbed, causing its contacts to be bridged by the mercury blob, the 555 latch is set to a high output level where it will stay even if the switch is returned to its starting position. The high output can be used to enable an alarm of the visual or the audible type. Switch S2 will silent the alarm and reset the latch. C1 is a ceramic 0.1uF (=100 nano-Farad) capacitor

Metronome: A Metronome is a device used in the music industry. It indicates the rhythm by a 'toc-toc' sound which speed can be adjusted with the 250K potentiometer. Very handy if you learning to play music and need to keep the correct rhythm up

Ten-Minute Timer: Can be used as a time-out warning for Ham Radio. The Federal Communications Commission (FCC) requires the ham radio operator to identify his station by giving his call- sign at least every 10 minutes. This can be a problem, especially during lengthy conversations when it is difficult to keep track of time. The 555 is used as a one-shot so that a visual warning indicator becomes active after 10- minutes. To begin the cycle, the reset switch is pressed which causes the 'Green' led to light up. After 10 minutes, set by the 500K potentiometer R1, the 'Red' led will light to warn the operator that he must identify