Re: 100khz sine wave into adc

by thefatmoop on Wed May 29, 2013 11:30 pm

played around with it and the problem is that I wasn't using a large enough cap. 10uF seems to do the job, but that's awfully large =/

That and there's either an op-amp bandwidth problem or it's the diode. I don't think it's the diode.

video here
http://youtu.be/MzKXaQ6AHoM
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Re: 100khz sine wave into adc

by adafruit_support_mike on Thu May 30, 2013 2:47 pm

Double-check the datasheet for your op amp and make sure your IN+ and IN- connections are correct. Tying the output back to IN- turns an op amp into a voltage buffer, which eliminates most of the supply-polarity issues.
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.
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Re: 100khz sine wave into adc

by gregn on Thu Nov 28, 2013 7:47 pm

thefatmoop wrote:
That and there's either an op-amp bandwidth problem or it's the diode. I don't think it's the diode.

video here
http://youtu.be/MzKXaQ6AHoM


Based on my experiences earlier this week with a simple peak detector circuit (just a diode, cap, & resistor), I think it's the diode. We saw exactly the same behavior as in your video, and checked the diode and found it to be the culprit. To check the diode, just hook it up in series with a resistor (i.e., diode followed by resistor) and put your AC voltage across the pair, measuring the voltage across the resistor while turning up the frequency. You'll see the voltage go from a half-wave rectified version of the input voltage to a DC voltage that drops to zero as you increase the frequency.
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