LIBRARYCapacitors and decoupling.
What a capacitor does, why a decoupling cap sits beside every chip, and the difference between ceramic and electrolytic. With real board examples.
A capacitor stores charge and releases it, which makes it the part that steadies a power rail. The decoupling capacitor beside almost every chip is the most common one you will place.
What does a capacitor do?
A capacitor stores an amount of charge for each volt across it, which is its capacitance in farads. It resists a sudden change in voltage, and it passes a changing signal while blocking steady DC. Those two behaviors cover almost every use.
Decoupling: the cap at every chip
A chip's current draw jumps the instant it switches. A small capacitor placed right at its power pins supplies that sudden demand locally, so the rail does not dip and the chip stays fed. That job is decoupling, also called bypass, and a 100 nF ceramic is the default choice.
Ceramic and electrolytic
Ceramic capacitors are small and fast, and the X7R type is temperature-stable (an EIA Class II dielectric), which is why X7R is the workhorse for decoupling (Murata). Electrolytic capacitors hold far more charge for bulk energy storage where power enters the board, at the cost of size and speed.
A Class II ceramic (X7R and its cousins) does not hold its rated value under a DC voltage. As the voltage across the part climbs toward its rating, its effective capacitance can fall by a large fraction, so a 100 nF part rated right at the rail delivers noticeably less than 100 nF in the circuit. The fix is free: pick a voltage rating well above the rail, a 10 V or 16 V part on a 3.3 V rail, and the capacitance you designed for is the capacitance you get. (Murata)
On a One Thousand Drones L1.01 board a 100 nF ceramic sits right at the module's power pins, and larger bulk capacitors sit where USB power enters.
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One Thousand Drones engineering team · verified 2026-07
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