How to · Microcontroller projects
Powering a project: the mistake that cooks a board
Power is the part of a microcontroller project that people skip, because on the bench it is a USB cable and it just works. Then the project has to run on its own, and it resets when the motor starts, or the sensor reads nonsense, or the board gets hot and dies. These are not mysterious. There is a short list of ways this goes wrong, and they have distinctive symptoms.
Before anything else: add up what your project draws, at its worst moment. Not its average — its peak. A board might draw 50 mA. A servo under load draws several hundred. A radio transmitting draws a burst far above its idle figure. A strip of addressable LEDs at full white draws considerably more than most people guess, and it is usually the LEDs.
Almost every power problem in this hobby is a peak that exceeds what the supply can deliver, at a moment lasting a few milliseconds. The average was fine. That is why it worked on the bench.
- Drawing motors or servos through the board — The 5V pin on a development board is usually the output of a small regulator, or a pass-through with a limit. Running a servo or a motor from it puts the peak current through that regulator and through the board’s traces. Symptom: it resets when the motor moves. Fix: power the motor from its own supply, and connect the grounds together — which is the step people miss, and without it nothing works at all.
- A regulator dropping too much voltage — A linear regulator turns the difference between input and output into heat, and the heat is the current multiplied by that difference. Feeding 12V into a board to get 5V at half an amp means the regulator is dissipating three and a half watts on a component the size of a grain of rice. Symptom: it gets very hot, then shuts down or dies. Fix: feed it a lower voltage, or use a switching regulator, which does not work by wasting the difference.
- No decoupling — A small capacitor close to the power pins of each chip supplies the short sharp current demands that the wires from the supply are too slow to meet. Without it you get resets and nonsense readings that come and go. Symptom: intermittent, worse when something else switches. Fix: a small ceramic capacitor at each chip, and a larger electrolytic where the power arrives on the board.
- Long thin wires, or a breadboard — Every wire has resistance, and current through resistance is voltage you do not get. A breadboard’s spring contacts add more, and they get worse with age. Symptom: works when you press on the wires. Fix: shorter and thicker power wires, and get anything drawing real current off the breadboard.
- Batteries at the wrong voltage for the job — A fresh alkaline cell is above its nominal voltage and a nearly flat one is well below. Four in series can start above what a board tolerates and end below what it needs. Symptom: works with new batteries, misbehaves as they age. Fix: a regulator between the batteries and the board rather than a direct connection, chosen for the voltage range the batteries will actually pass through.
- Alkaline: simple, fine for low draw, poor at peaks — Cheap, safe, available. Internal resistance rises as they discharge, which makes them bad at the sudden peaks a radio or a motor produces.
- A USB power bank: the easy answer, with one catch — Regulated 5V, protected, rechargeable, and no design work. The catch is that many power banks switch themselves off when the draw is low, which is exactly what a sleeping microcontroller does. This surprises people building battery projects for the first time.
- Lithium cells: the capable option, and the one with obligations — Far better energy density and much better at peaks. They also require correct charging, protection circuitry and appropriate handling, and getting that wrong is a fire rather than a failed project.
- Sleep is worth more than capacity — A project that wakes, reads, transmits and sleeps can run for months on cells that would last days if it stayed awake. If a battery project needs to last, the deep sleep current is the number that decides it, and it is a design decision rather than a battery choice.
Questions this guide answers
Listed so you can tell at a glance whether this is the page you wanted. HobbyHQ keeps one guide per question family rather than a page per phrasing.
- why does my microcontroller reset when the motor starts
- can I power a servo from the board 5v pin
- what voltage regulator do I need for my project
- how do I run an esp32 from a battery
- do I need a decoupling capacitor
- why does my board get hot when powered from a barrel jack
- how do I power a project from lithium batteries safely
Part of Microcontroller projects. Last reviewed 2026-08-22.