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Op-Amp Question

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Op-Amp Question

By Erkle
-  Sun Dec 05, 2010 12:48 pm #114909
I'm using an op-amp (LM358) to voltage follow a high impedance sensor and my question is this. What do I need to do on the op-amp output side to connect it to an Arduino analog input to read the voltages safely without burning anything up? Do I want to throw a resistor in between the op-amp and Arduino?

Stick Schematic:

[sensor}---{op-amp}---{? if any}---{Arduino]

Thanks ahead of time.

Re: Op-Amp Question

By waltr
-  Sun Dec 05, 2010 2:16 pm #114918
Just ensure that the op-amp's output voltage never exceeds the processor's input voltage limits.
A series resistor and diodes to the power + and ground is a common method.
What is the voltage powering the op-amp?

Re: Op-Amp Question

By Erkle
-  Sun Dec 05, 2010 2:47 pm #114920
vcc is 5v.

the probe on the non inverting side outputs a voltage between 0v and 3v.

Re: Op-Amp Question

By waltr
-  Sun Dec 05, 2010 8:57 pm #114941
Erkle wrote:vcc is 5v.

the probe on the non inverting side outputs a voltage between 0v and 3v.
Then you should be fine with just a small value resister is series to the ADC input. Try 50 to 200 Ohm. This R is to help keep the Op-amp from 'seeing' a capacitive load.
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