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Support Forum » Multiple sensor (LM34s) wiring

March 17, 2010
by Ralphxyz
Ralphxyz's Avatar

Not wanting to assume, since I know so little I thought I'd ask.

How do I wireup multiple sensors (LM34s)?

I need 5 temperature sensors, I know I will use PCO, PC1, PC2, PC3 and PC4. But what do I use for +Vs and GND do I use AREF and GND pins 21 and 22?

That would make sense but I was concerned about the "load". The LM34 has a "Less than 90 μA current drain" so that would give 450 μA.

Is the current coming from the MCU or from the power supply?

I still haven't gotten my programing for multiple sensors working yet so I will need help on that once I get the wiring set.

Thanks so much for the help I really appreciate it.

Ralph

March 18, 2010
by mrobbins
(NerdKits Staff)

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Hi Ralph,

For the +Vs and GND, the LM34's current consumption is so tiny that it doesn't matter too much where you draw it from. In any case, we simply used the AREF and GND pins because they were in proximity to PC0, but you don't have to! Because we have a wire connecting them to the red/blue rails, it really is equivalent.

You can just place your temperature sensors somewhere else on the breadboard, grab power/ground from the red/blue rails, and have little sensor wires heading back to the ADC input pins.

Hope that's clear!

Mike

March 18, 2010
by mongo
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They can all draw power from the +5V source. Each output would independently go to it's own MCU input and the ground side should be the same as AREF and it would be grounded. I would install a small capacitor at each LM34 to sink off stray noise between the +5 and AREF lines. Maybe something like .01 to .1 uF should do.

March 18, 2010
by Ralphxyz
Ralphxyz's Avatar

Great that is what I suspected but wanted to make sure.

Thank you all, Ralph

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