Automatic temperature based exhaust fan controller
Dsr
1.
2. contents
1. Introduction
2. Block diagram
3. Circuit diagram
4. List of components
5. Discription of IC’s
6. Working
7. Applications
8. Advantages
9. References
10. Conclusion
3. 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/cooler 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 or the cooler.
4. The device presented here makes the fan run at full
speed for a predetermined time. The speed is
decreased to medium after some time, and to slow
later on. After a period of about eight hours, the
fan/cooler is switched off.
11. WORKING
The circuit for the automatic speed controller for fans and coolers is shown in the figure.
➢
The supply voltage of 230V, 50Hz is given to the step down transformer and it is convertedto 9V. ➢
The bridge rectifier converts AC to pulsating DC supply and is filtered with smoothingcapacitor.
➢
In the circuit diagram IC1 (555 timer IC) act as an astable multivibrator. It is used togenerate clock pulses. The pulses are fed to a decade divider counter, which is formed byIC2
and IC3.
➢
These ICs act as divide by 10 counters and divide by 9 counters respectively. The valuesof capacitors C1, resister R2 and R2 are so adjusted that the final output of IC3 goes
highabout 8hours.
➢
The first two outputs of IC3 (Q0 and Q1) are connected through diode D1 and D2 to the base of the transistor T1. Initially output Q0 is high and there for relay RL1 is energized.
Itremains energized when Q1 becomes high. The method of connecting the gadget of the fanor cooler is given in the figure.
➢
Initially the fan shall get A/C supply directly so it shall be run at high speed. When theoutput Q2 becomes high and Q1 becomes low, relay RL1 is turned off and relay RL2
isturned on.
➢
The fan gets A/C through a resistance and its speed drops to medium. This continues untiloutput Q4 is high. When Q4 goes low and Q5 goes high, relay RL3 is activated thus
the fanrun at low speed. ➢
Throughout the process, pin 11 of the IC is low, so T4 is cut off, thus keeping T5 insaturation and relay RL4 is on. At the end of the cycle, when pin 11(Q9) becomes high T4get
saturated and T5 is cut off. Relay RL4 is switched off, thus switching of the fan or cooler.
SSCETEEE DEPARTMENTPage 49
AUTOMATIC SPEED CONTROLLER FOR FANS AND COOLERS
➢
Using the given circuit the fan shall run at high speed for a comparatively lesser time wheneither of Q0 or Q1 output is high. At medium speed it will run for a moderate time
periodwhen any of three outputs(Q2 to Q4) is high, while at low speed it will run for a muchlonger time period when any of the four outputs(Q5 to Q8) is high.
➢
It is possible to make the fan run at the three speeds for an equal amount of time byconnecting three terminal decoded outputs of IC3 to each of the transistors T1 to T3.
Onecan also get more than three speeds by using an additional relay transistor and associatedcomponents and connecting one or more outputs of IC3 to it.
➢
It has been designed to reduce the amount of electric power.
Circuit Diagram:
SSCETEEE DEPARTMENTPage 50
12.
13.
14. APPLICATIONS
Used to control the speed of fans and coolers
automatically.
This device can be used in bed rooms during night
hours.
This device can be used as a power saving system for
hotels and houses
15. ADVANTAGES
No manual support is needed, it is fully automatic.
Electrical energy can be saved to a greater extent.
Only less power is needed for the operation.
Lifetime of fan or coolers can be increased
17. CONCLUSION
The automatic speed controller for fans or coolers is
used to control the speedautomatically. We can also
assign different time periods for each speed by
designing the circuit tothe need. By using this circuit
the electric power can be saved to a greater extent and
increaselifespan of fans and coolers.
