thermistor interfacing

[ahsanali]

thermistor or lm35

in my project" THE BURGLAR AND FIRE FIRE ALARM"
I have to use micro controller( 89c51 ) which is must
bcz microcontroller is my subject in class.
and thus i have to interface LM35 thermistor/temp sensor.
So, i want to interface the LM35 and 89c51.
How is it possible?????????
My Project=To make a fire alarm using microcontroller such that
the user gives it a temprature value as a barrier ,and
the system should also sense the environmental temp.
and when the environmental temp exceedes that barrier
the alarm should be switched on.
this is the very first time for me to work with microcontroller
so i want to know that how the circuit will be made,its workig,
interfacing,diagram
I shall be very thank full to u all for this act of kindness

 

[Baslan]

adc interface into micro without ref

hi
to interface the LM35 into the micro you need to use analog to digital converter
ADC which converts the voltage produced by LM35 into digital value that you can read by the micro controller
note that LM35 gives (10 mV) change for (1 °C ) change and it has leaner response

Added after 11 minutes:

I think this link will help you ..
**broken link removed**

 

[IanP]

temperature sensor circuit using thermistor

If you have to use this particular microcontroller then you will have to select an external ADC, however if you are not then I would choose a microcontroller with built-in ADC. This solution simplifies your circuit and also software part of your project is much, much easier.
8 bit may be not enough for precisely sensing temperature with LM35 temperature sensor (10mV versus 19.5mV at 8 bits). Something like 10-bit converter would be probably better option.
If you would like to be stack with 8051 core then go to Maxim-Dallas web site ( www.maxim-ic.com ) and select a microcontroller there, or you can try www.microchip.com for similar product, if you can use the PIC core ..
In both cases you will be offered free samples ..

 

[electron_boy]

thermistor to micro interface

since the mcu is 8051 u have to use a 8 bit adc. the step voltage of 8 bit adc is 5v/256 = 19.5mV .and lm35 changes 10mv/0c so use a reference of 2.56mV so that the step voltage of the adc is 10mV and thus for each degee variation there will be change in the adc.
for more details refer "the 8051 microcontrollers and embedded systems"- mazidi

 

[Baslan]

interfacing thermistor

Hi
we can use an operational amplifier to make the sensor response greater
such as LM324 or LM741 by amplification factor of about ( 8 ) or ( 10 )

 

[electron_boy]

lm35 thermister

Hi
we can use an operational amplifier to make the sensor response greater
such as LM324 or LM741 by amplification factor of about ( 8 ) or ( 10 )

i think there is no need for amplifiers here. lm35 is linear and gives 10mv per degree rise. just changing the Vref of ADC is enough

 

[microcozmoz]

thermistor microcontroller

If u have a hance try to use pic microcontroller. I 've made with 16F877...

ADCON1 = %10000010' configure the port

Define ADC_BITS 10 ' ADC result is 10 bit
Define ADC_CLOCK 1 ' ADC clock source( foscillator/8 )
DEFINE ADC_SAMPLEUS 50 ' ADC sample time

DEG CON 223 ' for a degree sign

TEMPERATURE VAR WORD
AD_Rez VAR word ' result of the ADC is 16 bit
C VAR byte ' for adc conversion

The code above all the initial setups made for measuring with LM35


You can call your measuring routine using code below

GOSUB MEASURE_TEMP 'call the routine
LCDOUT $FE,$D4,dec2 AD_Rez,DEG,"C" 'display on the LCD

This is the routine to convert temperature..

MEASURE_TEMP:

ADCIN 0, AD_Rez '
AD_Rez = (AD_Rez */ 500)>>2 '

Return



I hope this will help u..