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Topic: conflicting advice on temperature sensors (Read 757 times) previous topic - next topic

novaris

ok, I am trying to use either the LM35 or lm335 sensor
but I see 2 different wiring diagrams for the sensor on different pages

http://guides.machinescience.org/mod/book/print.php?id=1348
says i need a 10k ohm resister with 1uF capacitor

http://mysite.du.edu/~etuttle/electron/elect23.htm
says I need i dont need anything

afremont

Both of those are ways to wire up an LM35, but not an LM335.  Read the datasheet.  The cap and resistor act like low-pass filter and also probably lowers the impedance when the sensor is read.  It would probably be more useful on long wiring situations to prevent oscillations.

I'm currently reading an LM34 using nothing but wires (no cap or resistor).  It's a little noisy, but over-sampling it takes care of that.  I think I'll try the cap and resistor and see if I can see any difference.
Experience, it's what you get when you were expecting something else.

novaris


Both of those are ways to wire up an LM35, but not an LM335.  Read the datasheet.  The cap and resistor act like low-pass filter and also probably lowers the impedance when the sensor is read.  It would probably be more useful on long wiring situations to prevent oscillations.

I'm currently reading an LM34 using nothing but wires (no cap or resistor).  It's a little noisy, but over-sampling it takes care of that.  I think I'll try the cap and resistor and see if I can see any difference.


thanks. but why is there 2 grounds for the first diagram? How do I connect them?

afremont

They just connect together and to the main system ground (GND) on the Arduiono.  It's not uncommon for a schematic to have many parts connected to ground (Vss) or the positive supply (Vcc).
Experience, it's what you get when you were expecting something else.

michinyon

All those grounds are the same,  connect them all together.   That is just a style of doing the drawings
so that it doesn't have a lot of extra lines on the drawing leading to one ground point.

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