plz help ...its urgent....

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ss53

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the lm35 with a negative voltage

hi
i am working on a microcontroller 89c51
i want to interface an LM35 to the microcontroller using an ADC
the temp range of the temp sensor is -55C to 150C(-550mV to 1.5V) with a scaling factor of 10mV/C.
the analog input to the ADC is 0-5V
my question is how are the negative voltage values converted on the ADC?
plz help ....its urgent
 

The ADC will not work with negative voltages ..
What you will have to do is to "mix" the output voltage from the LM35 with +550mV and one way of doing this is to use "adder" based on an opamp ..

Refer to this post for an example:


Regards,
IanP
 

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    ss53

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first shift the minimum voltage(-550mv? ) into zero volt by summing the sensor output with the +550mv(use a pot - potential devider) using a opamp summing amplifier (level shifting) .
now u get 0V to 2.05V(1500+550mv) range. so use an non inverting amlifier with the gain of > 5/2.05 to get 0-5V input to ur microcontroller
 

Instead of LM35, how about using LM335?

The LM335 transducer has 10mV/°K, so its output voltage will be positive even when measuring negative (°C) temperatures.
 

First detect that it is a -ve volatge and rectify the same..
 

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