temperature sensor...

[mugzzzzy]

hi,
i builded a temperature sensor using the LM35DZ which gives a 10mv per celcious connected to a ADC0804, and that connected to a LED's. ...
i used a voltage refence of 1.27v for the ADC...its is actually working...i took the voltage at the Vout of the LM35 of 0.24V ...that means its 24 degree in tha room and i got 24 in binary on the LED's...how come its working becuz ppl told me that i need a op-amp or a signal conditioning before it goes to the ADC


lemme know what ya think....

 

[Nigel Goodwin]

It depends on the actual spec of the device. Usually an A2D uses a 5V reference, so by using a 1.27V one you're effectively giving a gain of about 4 times. If 1.27V is the maximum output from the chip, that's ideal, your A2D will read the temperature directly, with no maths needed.

Another concern is the input impedance of your A2D, and the output impedance of your LM35DZ - as long as the input is considerably higher than the output, it should be fine.