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Sallen-Key Filter

A project log for AquaPic - Aquarium Controller

Reef tank controller used to monitor various parameters such as temp and pH, and also control equipment such as pump and lights.

skyler-brandtSkyler Brandt 08/04/2014 at 22:220 Comments

I breadboarded my PWM Sallen-Key filter, complete with crude hand drawn schematics.

That breadboard picture is pretty much just a bunch of wires. I really need to get better with my picture taking. The next two pictures are the frequency response from zero to full duty and full duty to zero. Both were around 10ms which I'm calling a win. But then I dialed back the duty on cycles and I got all kinds of oscillation.

Long story short, I don't have a sufficient capacitor collection and I can't read DMM. So what I thought was a 1uF cap was actually a 0.1uF, and I don't posses any 1uF caps. I changed out the 10K resistors with 1K resistors to account for my order of magnitude fail and oscillations all gone.

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