Temperature
Sensor-LM35
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Temperature sensor:
Commonly available temperature sensors are LM35,DS1621,thermistor.
Thermistor gives resistance proportional to the temperature. But
accuracy is not good in thermistor. DS1621 gives
digital output in I2C format, so you require a
microcontroller to interface to see the temperature. Thermistor
require accurate resistance in series to get good reading with accuracy
The resistance of thermistors are 100ohm,1Kohm(the
one i have heard). But thermistor creates some
headaches although it costs Rs.5. LM35 have 3
terminal Vcc, ground, Vout. So it is easy and gives analog output and it
costs Rs.50
LM35:
The most commonly
available LM35 is LM35DZ measures temperature from
0 to 100 degree. Normally sensors become inaccurate with age. But
LM35 will not have this problem. We get LM35 in TO-92 package, just
like small transistors like BC547. The main problem
you will be creating is
interchanging leads. Vs ranges from 4V to 30V. Output is 10mV* degree in
Celsius. That is if the temperature is 29 degree then Vout=.29V.
Let's try for a circuit which will glow an LED if
the output voltage is greater than some voltage.
Use comparator with a reference voltage at one end and
LM35 output at other end, so that comparator become high when the
temperature is above reference.
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