<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Use this website to design an active filter</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><a href="http://sim.okawa-denshi.jp/en/OPstool.php">http://sim.okawa-denshi.jp/en/OPstool.php</a> </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Here is what I would use unless you need fast response</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><span style="font-family:Arial,Helvetica,sans-serif"></span><br></div><div class="gmail_chip gmail_drive_chip" style="width:396px;height:18px;max-height:18px;background-color:#f5f5f5;padding:5px;color:#222;font-family:arial;font-style:normal;font-weight:bold;font-size:13px;border:1px solid #ddd;line-height:1"><a href="https://drive.google.com/file/d/1Tqvi3fRPWzvwn_f6gx6AD3zccl_0SlH6/view?usp=drive_web" target="_blank" style="display:inline-block;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-decoration:none;padding:1px 0px;border:none;width:100%"><img style="vertical-align: bottom; border: none;" src="https://ssl.gstatic.com/docs/doclist/images/icon_10_generic_list.png"> <span dir="ltr" style="color:#15c;text-decoration:none;vertical-align:bottom">Sallen-Key Low-pass Filter Design Tool - Result...</span></a></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><span style="font-family:Arial,Helvetica,sans-serif"></span> <br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Uses 2 x 1 Megohm resistors and 2 x 0.1 uF capacitors</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Super stable output probably from most normal PWM, but not very fast.  The signal stable in about a second after the PWM changes.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Use this opamp:</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><a href="https://www.digikey.com/product-detail/en/MCP6002-I%2FP/MCP6002-I%2FP-ND/">https://www.digikey.com/product-detail/en/MCP6002-I%2FP/MCP6002-I%2FP-ND/</a><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">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!</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">The DIP package makes it easy to use with a protoboard.<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">But any CMOS opamp with Rail to rail input and output performance and 5V single supply operation should work.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">There are other circuits that are similar </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><a href="https://www.electronics-tutorials.ws/filter/second-order-filters.html">https://www.electronics-tutorials.ws/filter/second-order-filters.html</a> </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">that let you adjust performance more but probably not worth it.<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">If you do not have a 5V power supply you might try this </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><a href="https://www.circuitlab.com/circuit/75p326/basic-peak-detector-01/">https://www.circuitlab.com/circuit/75p326/basic-peak-detector-01/</a>  </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">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.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Best</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small">Martin <br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small"><br></div></div>