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Loop created when using both scope channels with Discovery 2


Hi all,

I've run into an unexpected problem.    


It seems that when I use both scope channels within the same circuit (at least for this circuit) I get tons of 60Hz noise and its harmonics.  Using a single channel does not generate this kind of noise.


I am using a 3 channel DC supply plugged into 60hz wall power that feeds my breadboard circuit in two areas.  My breadboard circuit is a simple non-inverting op-amp whose input signal comes from a constant current source excited thermistor.  The gain is ~ 30 V/V.    I'm using the Analog Discovery 2.


Normally, I've been using the either channel to check my pre or post-amplified signal.  This single channel behaves normally.  Nice low frequency temperature response from my thermistor.

However, upon adding the other channel to look at the opposite end of my op-amp circuit, I get tons of 60Hz, 120Hz, etc. garbage.





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Hi Dan,

True,  I did not have the Discovery's ground hooked in.

Seems like I've confounded the issue now, however.  The single channel response has become way more garbled and I'm getting some inconsistent readings.  I feel like I've messed something up.  Will return when results are reproducible.




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