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Basic Electronics » lower voltage of sensor output LM335

August 20, 2013
by Osarus
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How do I get half the voltage of the output without affecting its value? I need it to reference with 3.3v on an ADC.

The LM335 is a temp sensor that outputs ~3v at 25 degrees celsius then 10mv/C How do I half the output which ranges from 2.35v-3.38v or get it under my 3.3v limit

I know I could use another sensor or use a higher vref but this makes life easier for me and I want to learn! Much appreciated :)

alt image text

August 20, 2013
by Noter
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A voltage divider would be the simplest method. Equal values for R1 and R2 will divide Vin in half.

voltage divider

August 20, 2013
by Osarus
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Won't that make another divider between what you suggest and R1, lowering the voltage LM335 gets affecting the result?

August 20, 2013
by Osarus
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Tested again with your suggestion

I removed the pot to make it simpler, the left circuit works correctly showing ~3v as it should for current temp. The right circuit shows the output from the device has been affected to 2.225v which is incorrect, half of that is more incorrect at 1.118v.

I THINK we have made another divider consisted on the 2k and 2.4k(the 2x 1.2k's) which is lowering the voltage to LM335 to 2.225v which is what its outputting meaning it cant output the higher voltage needed to represent the current temp.

alt image text

August 20, 2013
by Osarus
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O durrr... I just used 10k resistors insted for r1 and r2... works fine ;-)

Thanks guys

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