Transcript 555 TIMER

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HITENDRA JOSHI
PRITAM ,BHAVESH ,VRAJ
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,
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◦ Monostable
◦ Astable
FUNCTION OF EACH PIN TIMER REFER
TO MONOSTABLE MULTIVIBRATOR
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PIN 1 : GROUND
-all the measure voltage must refer to this pin
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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.
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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…..
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PIN 4 : RESET
- Reset with negative pulse
- When the reset pin is not used, the pin is connected to +Vs to avoid false trigger.
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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.
- 0.01µF capacitor can avoid from noise problem.
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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.
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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.
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PIN 8 : SUPPLY VOLTAGE, Vcc
- +5 V to 18V
555 TIMER INTEGRAL CIRCUIT
A view inside the 555 IC / Black Box
MONOSTABLE MULTIVIBRATOR
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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….
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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 ASTABLE MULTIVIBRATOR
CONTINUE…
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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 RA and RB.
ii) When capacitor voltage reach 2/3 Vee, Comparator 1 will trigger flip flop
and output change from change from HIGH to LOW. Resistor RB 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.
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FORMULA FOR TIMER
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TH = 0.693 (RA+RB) C
TL = 0.693 (RB) C
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Period, T = TH + TL = 0.693 (RA + 2RB) C
Frequency, f = 1/T
= 1/ (TH + TL)
= 1.44 / ((RA + 2RB) C)
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% Duty Cycle = [TH / (TH +TL) ]x 100
= [(RA + RB) / (RA + 2RB)] x100
555/556 Inverting Buffer
(Schmitt trigger) or NOT gate
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555 inverting buffer or NOT gate
NOT gate symbol
The buffer circuit's input has a
very high impedance (about
1MΩ) 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:
- Input low (< 1/3 Vs) makes
output high, +Vs
- Input high (> 2/3 Vs) makes
output low, 0V
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.
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555/556 Bistable (flip-flop) - a
memory circuit
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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.
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
http://www.uoguelph.ca/~antoon/gadgets/555/555.html
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 callsign 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 10minutes. 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