Capacitors

Every time a digital circuit switches state or a motor changes speed, it draws a sudden burst of current from the power rail. If no capacitor is nearby to supply that burst locally, the rail voltage dips for a few microseconds — long enough to cause an IC to misread data, an ESP32 to reset, or a microcontroller to crash.

Capacitors act as tiny local energy reservoirs. They charge up from the supply and discharge instantly into the circuit when a spike demand occurs, keeping the voltage level steady. This is called decoupling or bypass filtering.

In cockpit builds the problem is especially noticeable when servos, stepper motor drivers, and multiple shift registers share a power rail with microcontrollers — without bulk capacitors on that rail, servo movement often causes the ESP32 to reboot or drop its WiFi connection.

In practice, use both types together: a small ceramic cap close to the IC handles fast transients; a larger electrolytic further up the rail handles slow load variations and bulk energy storage.

The fundamental rule: as close as possible to the VCC/GND pins of the IC. Every millimetre of trace between the cap and the pin adds inductance that slows the cap's response. On a breadboard, place the cap in the adjacent row across the power rails.

Electrolytic capacitors are polarised. Connecting them backwards causes them to heat up, vent electrolyte, and sometimes burst. Always identify the positive terminal before soldering.

Every capacitor has a maximum voltage rating. Exceeding it causes dielectric breakdown — the capacitor fails, often violently. Always choose a capacitor rated for at least 1.5–2× the supply voltage to give a comfortable margin.

ESP32 Module on Breadboard

Add a 10 µF electrolytic and a 100 nF ceramic in parallel across the 3.3 V and GND rails of the breadboard, close to the ESP32. The ESP32's WiFi radio draws sharp 200 mA current bursts during transmissions; without this capacitor the onboard 3.3 V regulator struggles to maintain voltage, leading to unexpected resets and WiFi disconnections.

Stepper Motor Driver (A4988 / DRV8825)

The datasheets explicitly require a 100 µF electrolytic across VMOT and GND, placed as close as possible to the driver board. When the stepper motor brakes or reverses, it acts as a generator and pumps voltage back into the VMOT rail. Without this cap the resulting spike (sometimes 40–50 V on a 12 V rail) destroys the driver instantly.

Servo Rail (Multiple Servos)

Each servo can draw a 500 mA to 1 A stall current when moving under load. With four or more servos sharing a 5 V rail (e.g. throttle quadrant), add a 1 000 µF / 10 V electrolytic at the power distribution point. This prevents the voltage rail from drooping when several servos move at the same time, which would otherwise cause position jitter or ESP32 brownout resets.

Shift Register Chains (74HC595)

Each 74HC595 driving eight LEDs switches all outputs simultaneously when the latch pin fires. Place a 100 nF ceramic across VCC/GND of every 74HC595 chip. On a long chain of five or more chips also add a 10 µF electrolytic at the start of the chain.

Electrolytic capacitors are usually labelled directly (e.g. "100µF 16V"). Small ceramic capacitors use a 3-digit code where the first two digits are significant figures and the third is the power of 10 multiplier in picofarads (pF).