ProcirelPowering Arduino Projects: USB, Battery and Supply Design
Most “broken” Arduino projects are under-powered projects. Between the input voltage window, the onboard regulator’s thermal limit and the current a project actually peaks at, supply design deserves the same care as the code.
> At a glance: 8 minute guide · part 10 of 10 in the complete Arduino guide track · includes a worked example and a quick-reference table.
## Input options and limits
USB delivers a regulated 5 V. The barrel Vin accepts 7–12 V (16 V absolute), feeding an onboard linear regulator that turns the difference into heat 12 V into a 200 mA project dissipates 1. 4 W in a small regulator. The 5 V pin accepts regulated 5 V directly, bypassing it.
| S | o | u | r | c | e | | | |
| — | — | — | — | — | — | — | — | — |
| V | o | l | t | a | g | e | | |
| G | o | o | d | | f | o | r | |
| W | a | t | c | h | | o | u | t |
| USB power bank | 5 V | Logic-only projects | Sleep-mode auto-off | | | | | |
| 2S LiPo + buck | 5 V / 3.3 V | Robots, portable | Brownouts on motor stall | | | | | |
| 9 V PP3 | 9 V | Almost nothing | Tiny capacity, weak peaks | | | | | |
| Wall adapter 9 V DC | 9 V | Desk projects | Unregulated cheaps ones sag | | | | | |
| Bench supply | Set | Development | Current limit is your friend | | | | | |
## Budgeting current
Sum the loads. Board ~50 mA, LEDs 10–20 mA each, servo peaks 1 A, radios 100–500 mA bursts. Design the supply for the peaks, not averages. Measure the real draw with a USB meter two minutes that prevents a week of debugging resets.
## Battery strategies
A 2S LiPo through a 5 V buck regulator is the standard for portable builds. 9 V PP3 batteries are a trap: ~500 mAh and poor discharge for motors. Compute runtime as capacity × 0. 8 ÷ average current, and budget the radio’s transmit bursts with local bulk capacitance.
## How to apply this in your build
Work through the sequence below each step assumes the previous one passed. For numbers that need calculating, the linked tools at the end of this guide do the arithmetic instantly.
1. List every load and its peak current
2. Choose a supply rated 30 % above the sum of peaks
3. Regulate locally where noise matters (radios, ADC)
4. Add bulk capacitance near burst loads
### Worked example
A GPS logger drawing 80 mA average from a 2500 mAh power bank: 2500 × 0. 8 ÷ 80 ≈ 25 hours but the bank’s auto-shutoff may cut it sooner than the maths says. Run the numbers yourself with the Battery Life Calculator and the result should agree to within rounding.
> Practical note from the bench. Every Procirel portable build carries the same sheet: peak current table, measured runtime, and the supply rails each block owns.
## Common mistakes to avoid
– Powering motors and servos from the onboard regulator
– Believing a 9 V PP3 can drive wheels
– Ignoring radio transmit bursts until brownouts appear
## Key takeaways
– Input options and limits the foundation of this guide; revisit it if any measurement here surprises you.
– Budgeting current the foundation of this guide; revisit it if any measurement here surprises you.
– Battery strategies the foundation of this guide; revisit it if any measurement here surprises you.
## Prerequisites and preparation
Before starting: list every load and its peak current and choose a supply rated 30 % above the sum of peaks. Keep the [Battery Life Calculator](/tools/battery-life) and [LM317 Regulator](/tools/lm317-regulator) open every number in the worked example is reproducible. Total time including the bench steps: about 6–8 minutes.
## Who benefits most
Hobbyists meeting this topic for the first time, students who want the version with real numbers instead of abstract symbols. Returning engineers refreshing a corner of the craft. The mistake list alone justifies the visit every entry in it was learned the expensive way.
### Quick reference card
| Aspect | Where to find it in this guide |
| — | — |
| Core theory | Input options and limits |
| Application steps | How to apply this in your build |
| Worked numbers | Worked example |
| Failure modes | Common mistakes to avoid |
## How this fits the complete Arduino guide track
This guide is one stop in the structured learning path. Start from the [complete Arduino guide](/tutorial/arduino-complete-guide) pillar page for the full map, or continue with [servo power requirements](/tutorial/arduino-servo-motor-control) and [buck converter basics](/tutorial/buck-converter-basics). For the arithmetic, open the [Battery Life Calculator](/tools/battery-life) or [LM317 Regulator](/tools/lm317-regulator).
## Frequently asked questions
Can I feed 5 V into the 5 V pin?
Yes, if the source is a clean regulated 5 V this bypasses the onboard regulator and is the normal route for USB-powered builds.
Why does my project reset when the motor starts?
The motor’s inrush sags the shared rail below the brownout threshold separate rails or bulk capacitance fix it.
Is there a calculator for this?
Yes the [Battery Life Calculator](/tools/battery-life) and [LM317 Regulator](/tools/lm317-regulator) tools run the formulas from this guide instantly, client-side, with no signup.
## What to read after this
– The complete arduino & microcontrollers guide: [Arduino & Microcontrollers complete guide](/tutorial/arduino-complete-guide)
– Read next: [what is an embedded system? microcontrollers in everything](/tutorial/what-is-embedded-system)
– Also in this track: [esp32 vs stm32: choosing your next microcontroller](/tutorial/esp32-vs-stm32-comparison)
– Continue with: [arduino ide 2 setup: from download to first upload](/tutorial/arduino-ide-setup-guide)
– Calculate as you go: [LED series resistor finder](/tools/led-resistor) · [battery runtime estimator](/tools/battery-life) · [555 frequency calculator](/tools/timer-555-astable)
– From here, the natural continuation is the next guide in the track index. It assumes exactly the vocabulary this page built and adds the next layer of practice.
## Field notes
The fastest way to internalise this topic is to change one variable deliberately and predict the result before measuring. Wrong predictions are the curriculum, they show exactly which mental model needs revisiting, and the bench grades honestly.
Component substitution is a legitimate experiment as long as it is deliberate. Swap one part, predict the effect, measure, and record. That single habit converts a parts bin into a teaching lab and makes every future guide in this track faster to absorb.
## Formulas and checks from this guide
Verification checklist for this track. Check pin assignments against the sketch header before wiring, confirm supply polarity twice. Serial-print one variable at a time when debugging. Keep each sketch’s pin map in a comment block so the next build inherits working documentation.
Bookmark this page against your next build in the track. The checklist above is the same one used across 15 guides in this series.
## Field lessons worth keeping
Anything with motors, servos or many LEDs needs external supply with common ground. USB is for logic only.
Uninitialised variables and pins left floating. Set every pinMode and initial state in setup.