---
title: Powering a MicroPython board
lang: en
type: tuto
phases:
  - concept
  - preuve-de-concept
  - dossier-technique
  - integration-et-tests
tags:
  - eee
  - tuto
  - micropython
prerequis:
  - micropython-prise-en-main-en
aa:
  - RA-PROJET-C03-3/PROJ/5
draft: false
source_fr: embarque/mcu/micropython/micropython-alimentation.md
source_sha256: 683b4dd4e1ec4d4f4500292a225f1d19822a2fcf0174f2e900a07d77e2aa0727
---

**Powering a Pico** means giving it the voltage and the current it needs to start, run its program, and feed the external components. The layout differs from an Arduino: no barrel jack and no 7805 linear regulator, but three key pins — **VBUS** (5 V from USB), **VSYS** (system input, 1.8–5.5 V) and **3V3(OUT)** (regulated 3.3 V output) — around a *buck-boost* regulator that makes the internal 3.3 V. Picking the right path — and sizing it — is the first thing to check when a project reboots on its own or refuses to start.

## What is it for?

As long as a project sits on a breadboard powered over USB, all is well. As soon as motors, relays, wireless modules or a display come in, the current climbs, and the Pico's 3.3 V output quickly reaches its limits. Knowing the power paths lets you **pick the right source**, **separate the supplies** when actuators disturb the logic, and **anticipate the peaks** (Wi-Fi transmitting, a motor starting).

## Step by step

Four steps: pick the path, estimate the current, wire it, check stability.

### 1. Pick the power path

| Pin | Role | Range | Use |
|---|---|---|---|
| **VBUS** (pin 40) | 5 V coming from USB | 5 V (if USB is plugged in) | pass the USB 5 V on to a 5 V module |
| **VSYS** (pin 39) | system input (to the internal regulator) | **1.8 – 5.5 V** | power the Pico from a battery or an external source |
| **3V3(OUT)** (pin 36) | regulated 3.3 V **output** | 3.3 V, limited current | power 3.3 V sensors and modules (light loads) |
| **3V3_EN** (pin 37) | enables the 3.3 V regulator | tied to GND = **off** | a software power switch |

**Basic rule**: USB as long as it is enough; otherwise **VSYS** (1.8–5.5 V) for an external source or a battery. The `3V3(OUT)` pin is an **output**, not an input. You do not inject a voltage into it.

### 2. Estimate the total current

Add up the consumptions, estimated on the **high** side:

- **Pico alone**: about 25–40 mA.
- **Simple sensors** (DHT11, HC-SR04): 1–15 mA each.
- **SG90 servo**: 10 mA at rest, 100–200 mA while moving, up to 500 mA when stalled.
- **Relay module**: 70–80 mA when it pulls in.
- **DC motor**: 100 mA to several amps.
- **Wi-Fi (Pico 2 W) transmitting**: peaks of several hundred mA.
- **WS2812 LED strip**: 3–5 A at full white — a dedicated supply is mandatory.

The **3V3(OUT)** output only delivers a few hundred mA (shared with the Pico itself): **do not hang a heavy load on it**. Beyond that, power the load separately (from VBUS/5 V or from a dedicated supply). For the general sizing method (power budget, margins), see [[alimentation-electronique-en|designing a power supply]].

### 3. Wire it

**USB**: a data cable. It brings 5 V onto VBUS, which feeds VSYS through a diode (VSYS ≈ 4.7 V), and the regulator then makes the 3.3 V.

**Battery or external source**: connect the source (1.8–5.5 V) to **VSYS** and its ground to **GND**. A single **LiPo** cell (3.0–4.2 V) or a pack of **2–3 AA cells** (3–4.5 V) fall straight inside the VSYS range. *If USB may also be plugged in at the same time, feed VSYS through a Schottky diode* (the higher source wins, with no conflict) — see the "Powering Pico" note in the datasheet.

**5 V module**: power it from **VBUS** (5 V, USB present), share GND, and shift its output signals down for the Pico ([[niveaux-de-tension-en|logic levels]]).

![The two power inputs of a Pico: USB 5 V arrives on VBUS and crosses an internal diode before VSYS, which then sits at about 4.7 V; an external source of 1.8 to 5.5 V connects straight to VSYS and GND, through a Schottky diode if USB may be plugged in at the same time. Both paths meet on VSYS, which feeds the 3.3 V regulator and the 3V3(OUT) pin.|640](/ressources/img/micropython-alimentation/deux-sources.svg)

### 4. Check stability

With a multimeter: **3V3(OUT)** should read about 3.3 V (3.2–3.4 V). **Under load** (with an actuator running), it must not sag. The typical symptom of a weak supply: **the Pico reboots as soon as an actuator kicks in** (the current peak pulls the voltage below the threshold — *brown-out* — and the board resets, then starts again).

## Example — A battery-powered project: Pico plus 3 modules

**Estimate**: Pico 30 mA + DHT11 2.5 mA + OLED 20 mA + servo 200 mA peak ≈ **250 mA** at peak.

**Choice**: a single-cell LiPo battery (3.0–4.2 V) on **VSYS**; DHT11 and OLED powered from **3V3(OUT)** (≤ 30 mA each, fine); servo powered **separately** (its peak would pull the 3.3 V down).

```python
from machine import Pin, PWM
servo = PWM(Pin(15)); servo.freq(50)   # servo on GP15, 50 Hz
# ... read sensors, drive the OLED, drive the servo
```

On the first attempt, powering the servo from 3V3(OUT) as well makes the Pico reboot whenever it moves. **Fix**: power the servo from a dedicated 5 V source (or from VBUS if USB is present), with **GND shared** with the Pico. See [[micropython-servomoteur-en|servo]] for good practice on servo supplies.

![Separate servo supply with a shared ground: the servo is powered from a dedicated 5 V source (VBUS or an external supply), only the signal comes from the Pico's GP15, and every ground (Pico, source, servo) is tied together — a shared GND.|560](/ressources/img/micropython-alimentation/alimentation-separee.svg)

## Pitfalls

**Injecting a voltage into 3V3(OUT).** It is an **output**: applying a voltage to it can damage the regulator. To power the Pico externally, go through **VSYS**.

**Going above 5.5 V on VSYS.** The VSYS range is 1.8–5.5 V. Applying 7–12 V (the "Arduino jack" reflex) destroys the board. There is no 7805-style input regulator here.

**A PC's USB port for actuators.** A reboot when an actuator kicks in is a diagnosis to make **before** hunting for a software bug. Fix: an external supply.

**A hungry load on 3V3(OUT).** That output is limited (a few hundred mA, shared with the Pico). A heavy load pulls it down, hence a brown-out. Power the load separately.

**An unanticipated Wi-Fi transmit peak** (Pico 2 W). Short peaks, invisible on a multimeter. A decoupling capacitor near the supply absorbs the peak and steadies things.

**No shared GND.** With two supplies (Pico plus load), GND has to be *shared*, otherwise the signals have no common reference and the system does not work.

## Special case — Batteries for standalone projects

- **2–3 AA cells** (3–4.5 V) → straight onto VSYS, available anywhere and replaceable without a tool;
- **a single-cell LiPo** (3.0–4.2 V) → straight onto VSYS, but it needs a dedicated charger and some care (over-discharge);
- to save power on a battery during long idle periods, see [[deep-sleep-en|deep sleep]] and [[micropython-deep-sleep-en|deep sleep on MicroPython]].

## Where it fits in the project

- **Step 4 of the [[concept-en|concept phase]]** — power is one of the deciding criteria (USB versus standalone, a plugged-in demo versus a mobile one).
- **Step 2 of the [[preuve-de-concept-en|proof of concept phase]]** — at the first power actuator, estimate the consumption and resize.
- **Step 4 of the [[dossier-technique-en|technical design file phase]]** — the final supply for the demonstrator (with margin) is part of the BOM.
- **Step 2 of the [[integration-et-tests-en|integration and testing phase]]** — check that the 3.3 V holds up under load on the integrated system.

Power is the most underestimated part of a beginner's project — ignored while all goes well, blamed wrongly when some other bug shows up. Measuring it with a multimeter at the first suspicious symptom saves hours of wandering.

## See also

- [[micropython-en|MicroPython]] — the module hub
- [[micropython-prise-en-main-en|Getting started]] — where USB power is met first
- [[micropython-deep-sleep-en|Deep sleep]] — cutting consumption for battery life
- [[micropython-shield-en|Expansion board]] — the plug-on board that pushes consumption up
- [[niveaux-de-tension-en|Logic levels]] — 3.3 and 5 V living together
- [[alimentation-electronique-en|Designing a power supply]] — the cross-cutting principles applied here
- [[lire-une-datasheet-en|Reading a datasheet]] — finding the nominal currents of the components
- [[arduino-alimentation-en|Powering an Arduino board]] — the equivalent (USB / jack / Vin)