Step 2: Low-Pass Filter¶ R31 and C9 form a low-pass filter. Tools Needed¶ Soldering iron Cutter Parts Needed¶ 1 x 4.7kΩ resistor 1 x 0.1μF capacitor Instructions¶ Solder the 4.7kΩ resistor into R31. Solder the 0.1μF capacitor into C9.