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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, June 01, 2021 03:06 PM
Hobby Circuits List
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Temperature Sensors;
Motor
Controls;
Control Circuits;
Voltage
Comparators |
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12V Cooling Fan
Thermostat January
29, 2011 |
This circuit will
turn on a 12v DC powered cooling fan when the air temperature reaches a certain high
temperature and will keep the fan turned on until the temperature drops below a
second lower level. Both the high and low temperatures are both adjustable.
For ease of use, the temperatures are proportional to either degree F or degrees C,
using an accurate electronic sensor. |
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A LM34 is used for
those wishing to measure the temperature in degrees F. A LM35 is used for
those wishing to measure the temperature in degrees C. The output of the LM34
is scaled for 10mv per degree F so 100 degrees will produce a voltage of 1.00v.
The output of the LM35 is scaled for 10mv per degree C so 20 degree C will produce a
voltage of 0.2v. This voltage can be measured at test point #1. At test
point #2, both the high and low switch points can be measured and adjusted. By
pressing the small pushbutton switch S1, while measuring the test point 2, the
circuit’s low switch point can be adjusted. Be sure to adjust the high
temperature first, then the lower one, since the first temperature setting will
affect the second.
One half of a LM393 dual voltage comparator is used to decide when to
turn on the fan motor. A p-channel MOSFET Q2 routes power to the fan when the
voltage comparator changes state. Q1 switches in a second resistor network to
change the temperature set point when the comparator A3 changes state and turns on
the fan motor. |
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Click on Circuit Below to view PDF of Schematic |
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More:
Temperature Sensors;
Motor Controls;
Control
Circuits;
Voltage
Comparators
. . . Hobby Circuit designed
by Dave Johnson
eMail David A.
Johnson, P.E. about this circuit |
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