Use this website to design an active filter http://sim.okawa-denshi.jp/en/OPstool.php
Here is what I would use unless you need fast response Sallen-Key Low-pass Filter Design Tool - Result... <https://drive.google.com/file/d/1Tqvi3fRPWzvwn_f6gx6AD3zccl_0SlH6/view?usp=drive_web> Uses 2 x 1 Megohm resistors and 2 x 0.1 uF capacitors Super stable output probably from most normal PWM, but not very fast. The signal stable in about a second after the PWM changes. Use this opamp: https://www.digikey.com/product-detail/en/MCP6002-I%2FP/MCP6002-I%2FP-ND/ it is $0.33 for 1 they have thousands in stock today. Digikey ships fast by low cost USPS to RDU area, typically 2-day to my home! The DIP package makes it easy to use with a protoboard. But any CMOS opamp with Rail to rail input and output performance and 5V single supply operation should work. There are other circuits that are similar https://www.electronics-tutorials.ws/filter/second-order-filters.html that let you adjust performance more but probably not worth it. If you do not have a 5V power supply you might try this https://www.circuitlab.com/circuit/75p326/basic-peak-detector-01/ to generate close to 5V power from your incoming PWM signal. With a large enough capacitor it probably will work if the PWM source is strong. Best Martin
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