AUTOMATIC SPEED CONTROLLER F0R FANS INTRODUCTION During summer nights, the temperature is initially quite high. As time passes the temperature starts dropping. Also, after a person falls asleep, the metabolic rate of one’s body decreases. Thus, initially the fan needs to be run at full speed. As time passes, one has to get up again and again to adjust the speed of the fan. This interferes with his/her sleeping period and thus he/she may not get sufficient rest leading to mental strain. The circuit presented here helps to overcome the above problem. Here the fan runs at full speed for a predetermined time. The speed is decreased to medium after some time, and to slow later on. After certain period the fan is switched off. This circuit consists of IC1 (555), which is used as an astable – multivibrator to generate clock pluses. The pulses are fed to decade divider/counter formed by IC2 (4017B) which is a 5-stage counter having 10 decoded output. The values of capacitors and resistors of the multivibrator circuit are so adjusted that the final output of IC2 goes high after the predetermined period. First the fan runs at high speed for a particular period of time. Then the fan speed Dept. of Electronics & Communication Engg. SJCET, Palai Page 1
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AUTOMATIC SPEED CONTROLLER F0R FANS
INTRODUCTION
During summer nights, the temperature is initially quite high. As time passes
the temperature starts dropping. Also, after a person falls asleep, the metabolic rate of
one’s body decreases. Thus, initially the fan needs to be run at full speed. As time
passes, one has to get up again and again to adjust the speed of the fan. This interferes
with his/her sleeping period and thus he/she may not get sufficient rest leading to
mental strain.
The circuit presented here helps to overcome the above problem. Here the
fan runs at full speed for a predetermined time. The speed is decreased to medium
after some time, and to slow later on. After certain period the fan is switched off.
This circuit consists of IC1 (555), which is used as an astable – multivibrator to
generate clock pluses. The pulses are fed to decade divider/counter formed by IC2
(4017B) which is a 5-stage counter having 10 decoded output. The values of
capacitors and resistors of the multivibrator circuit are so adjusted that the final output
of IC2 goes high after the predetermined period. First the fan runs at high speed for a
particular period of time. Then the fan speed reduces to a medium .After some time to
a low value and then turns off. The speed control is achieved with the help of
transistor- relay arrangement. The transistor on/off is controlled with the help of the
diodes connected to the timer circuit. Whenever the transistor gets on it is connected
to the relay and the fan runs according to counter output.
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AUTOMATIC SPEED CONTROLLER F0R FANS
1 . BLOCK DIAGRAM
1.1 BLOCK DIAGRAM REPRESENTATION
fig
Figure. 1 block diagram of automatic speed controller for fans
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Power supply
Astable Multivibrator
Counter
Fan
Speed
Regulator
Transistor-Relay arrangement
AUTOMATIC SPEED CONTROLLER F0R FANS
1.2 BLOCK DIAGRAM EXPLANATION
POWER SUPPLY UNIT
ac dc o/p
Figure. 2 block diagram of power supply unit
The function of this unit is to provide sufficient power for the proper
functioning of the device. The power supply section provides a dc voltage of 6v.The
transformer is a step down transformer for low output voltage. The filter circuit
converts output of transformer to pulsating dc.The filter component smoothens output
and the regulator provides a regulated dc supply output.
ASTABLE MULTIVIBRATOR
IC NE555 is configured as astable unit. This unit produces a clock pulse. The
clock pulses are given to the counter circuit. The known values of capacitors and
resistors are placed in the shorted pins 6 and 7 of IC NE555 and ground. This circuit
does not require an external trigger to change the state of the output, hence the name
free-running. The time during which the output is either high or low is determined by
two resistors and capacitor, which are externally connected to the 555 timer.
COUNTER SECTION
This section receives the clock pulse from the astable unit. It uses a five stage
decade counter IC CD4017B having 10 decoded outputs. It acts as a ring counter. The
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Transformer Rectifier Filter Regulator
AUTOMATIC SPEED CONTROLLER F0R FANS
counter output is connected to the regulator circuit through the transistor-relay
arrangement.
TRANSISTOR-RELAY ARRANGMENT
The fan speed is controlled by this section. Here this section determines the
speed levels by turning on and off the transistor –relay arrangement.
REGULATOR CIRCUIT
Regulator circuit is an electrical step one. In electrical regulator by using
resistance output voltage is varied simultateneouly the speed is varied. But to reduce
the energy loses in the resistor; electronic regulator is introduced, which uses triac to
vary the output voltage by varying the firing angle, which avoids lose of energy in
resistor.
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AUTOMATIC SPEED CONTROLLER F0R FANS
2. CIRCUIT DESCRIPTION
2.1 POWERSUPPLY
Figure. 3 power supply unit
2.1.1 Description
The simple circuit of power supply is used here. A step down transformer is
used here for low output voltage .It provides the required magnitude of dc voltage.
The 230v is stepped down to 6v by the transformer
The transformer output is given to a rectifier circuit consisting of diodes
connected as a bridge. The bridge circuit rectifies ac input voltage to dc voltage. The
bridge network rectifies both half cycles of ac input voltage thus producing a
pulsating dc voltage.
Since pulsating dc voltage contains both dc as well as ac components, it is
necessary to remove the ac components. The filter circuit minimizes the ripples in the
rectified supply capacitor is used here.
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AUTOMATIC SPEED CONTROLLER F0R FANS
The filtered output is given to regulator circuit. A regulator IC7806 is used
here. They do not require an external reference voltage. The device has three
terminals marked as input terminal, ground terminal, and output terminal.
2.2 CIRCUIT DIAGRAM
Figure. 4 circuit diagram
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AUTOMATIC SPEED CONTROLLER F0R FANS
2.3 CIRCUIT EXPLANATION
Using the circuit we can control the speed of the fan automatically .Here IC1
(555) is used is an astable multivibrator to generate clock pulses. The pulses are fed to
decade dividers/counters formed by IC2. The IC2 act as ring counter. The values of
capacitor C1 and resistors R1 and R2 are so adjusted that the final output of IC2 goes
high after a predetermined time. The first two outputs of IC2 (Q0andQ1) are
connected via diodes D1 and D2 to the base of transistor T1. Initially output Q0 is
high and therefore relay RL1 is energized.
Initially the fan shall get AC supply directly, and so it shall run at top speed.
When output Q2 becomes high and Q1 becomes low, relay RL1 is turned off and
relay RL2 is switched on. The fan gets AC through a resistance and its speed drops to
medium. This continues until output Q4 is high. When Q4 goes low and Q5 goes
high, relay RL2 is switched off and relay RL3 is activated. The fan now runs at low
speed. Throughout the process, pin 11 of the IC is low, so T4 is cut off, thus keeping
T5 in saturation and RL4 on. At the end of the cycle, when pin 11 (Q9) becomes high,
T4 gets saturated and T5 is cut off. RL4 is switched off thus switching off the fan.
Using the circuit described above, the fan shall run at high speed for a
comparatively lesser time when either of Q0 or Q1 output is high. At medium speed,
it will run for a moderate time period when any of three outputs Q2 through Q4 is
high, while at low speed, it will run for a much longer time period when any of the
four outputs Q5 through Q8 is high. If one wishes, one can make the fan run at the
three speeds for an equal amount of time by connecting three decimal decoded
outputs of IC2 to each of the transistors T1 to T3. One can also get more than three
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AUTOMATIC SPEED CONTROLLER F0R FANS
speeds by using an additional relay, transistor, and associated components, and
connecting one or more outputs of IC2 to it.
3. COMPONENETS AND SPECIFICATION
3.1 COMPONENTS LIST
NO ITEM SPECIFICATION QUANTITY
1 IC1 NE555 1
2 IC2 CD4017B 1
3 Resistor 47kΩ 1
4 Resistor 22kΩ 2
5 Resistor 10kΩ 4
6 Diode 1N4001 13
7 Capacitor 220µf 1
8 Capacitor 0.01µf 1
9 Transistor BC548 5
10 Relay 6v,100Ω,Spdt 4
11 Fan Regulator Step 1
12 Transformer Step down (0-12v) 1
13 Capacitor 0.01 µf 1
14 Capacitor 1000 µf 1
15 IC LM7806 1
16 Round bridge rectifier 1A 1
17 Led 1
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AUTOMATIC SPEED CONTROLLER F0R FANS
4. PCB DESIGN AND FABRICATION
4.1 Printed Circuit Board
PCB is a platform where the electronic component can be inter connected
without wiring. PCBs make the electronic circuit manufacturing an easy one. In older
days vast area was required to implement a small circuit to connect the leads of the
components and separate connections were needed. But PCBs connect the two, by
copper coated lines on the PCB. In the single sided PCBs the copper layer is on one
side.
4.2 Board Types
The most popular board types are:
4.2.1 SINGLE-SIDED BOARDS: They mainly used in entertainment electronics
where manufacturing costs have to be kept the minimum.
4.2.2 DOUBLE-SIDED BOARDS: Double sided PCBs can be made with or without
plated through holes. The production of boards with plated through holes is fairly
expensive.
4.3 Manufacturing Process
First, the PCB layout of the required circuit is designed. The PCB layout is
then drawn on the plane copper coated board. These boards are available in two types.
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AUTOMATIC SPEED CONTROLLER F0R FANS
1. Phenolic
2. Glass epoxy
Most computers, PCBs are glass epoxy. To draw the layout we can use black
color paints. Before that the required size of the plane PCB board is determined from
the roughly drawn PCB layout. Using black paint the desired layout is drawn on the
PCB.
4.4. Layout Approach
The first rule is to prepare each and every PCB layout as viewed from the
component side. Another important rule is to start the designing of a layout unless an
absolutely clear circuit diagram is available, if necessary, with a component list.
Among the components the larger ones are placed first and the space between
is filled with similar ones. Components requiring input/output connections come near
the connectors. All components are placed in such a manner that desoldering of other
components is not necessary if they have to be replaced.
In the designing of a PCB layout it is very important to divide the circuit into
functional subunits. Each of these subunits should be realized on a defined portion of
the board. In the designing in the inner connections which are usually done by pencil
lines, actual space requirements in the artwork must be considered. In addition the
layout can be rather roughly sketched and will still be clear enough for artwork
designer.
Board Cleaning
The cleaning of the copper surface prior to resist applications is an essential
step for any types of PCB process using etch or plating resist. Insufficient cleaning is
one of the reasons most often encountered for difficulties in PCB fabrication although
it might not always be immediately recognized as this. But it is quiet often the reasons
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