# Arduino to custom PCB: choose your first board architecture

> Move an Arduino prototype to a custom PCB: compare shields, carrier boards and integrated designs, then prepare pin mappings, programming and acceptance checks.

Source: https://ohmbo.com/blog/arduino-to-custom-pcb

Moving from Arduino to a custom PCB starts with a choice: keep the development board, mount a module on a carrier, or move the microcontroller and its support circuitry onto your own board. Choose based on what the next prototype needs to prove. Replacing jumper wires requires a different amount of work from fitting all electronics into a small enclosure.

This guide helps you select that architecture and prepare a design handoff. Bring the working hardware, its exact board and module names, the firmware revision and a connection list. A running sketch is useful evidence, but it does not describe every electrical function supplied by the development board.

## Choose what your custom PCB will replace

A shield or carrier can be a useful first revision when connector placement and repeatable wiring matter more than minimum size. A fully integrated board gives you control over the electronics and outline, but also makes you responsible for functions the development board previously handled.

| Approach | What remains | What to review before choosing it |
| --- | --- | --- |
| Shield for the existing board | The development board and its firmware-loading connection | Header compatibility, connector height and access inside the enclosure |
| Carrier for a selected module | A specific module mounted on the custom board | Module footprint, supply and signal requirements, mounting and programming access |
| Integrated microcontroller board | The required chip and support circuits selected for your design | Power, clock, reset, programming, pin assignments and firmware compatibility |

Start with the least extensive change that answers your prototype question. If the purpose is to evaluate the user interface in a handheld enclosure, an oversized carrier may be unsuitable. If the purpose is to distribute several wired sensor prototypes to colleagues, integration can wait until their feedback justifies it.

Do not treat a development board as a single chip. For example, the [official Arduino UNO R3 documentation](https://docs.arduino.cc/hardware/uno-rev3/) lists a USB connection, power jack, ICSP header and reset button, and provides its schematic, pinout and CAD resources. Use the documentation for your exact board revision to identify what you rely on. Other Arduino boards need their own review. Source checked: 2026-10-19.

## Record connections before changing the hardware

Create a signal table that connects the firmware to the physical design. For every used signal, record the sketch's pin name, development-board connector pin, target device pin, signal voltage, direction and attached peripheral. Add any required startup state or externally fitted resistor.

This catches ambiguities that a wiring photograph leaves unresolved. A connector labelled “sensor” does not identify its pin order or whether its signals require level translation. A library configuration may contain a pin assignment that never appears in your handwritten notes.

Keep the first revision focused. Changing the processor, sensor, supply and application code together makes a failed demonstration harder to diagnose. When a change is necessary, record the reason and the check that will show it works. The [first-prototype guide](/blog/first-custom-pcb-prototype) covers the broader requirements brief; this signal table is the migration-specific addition.

## Preserve firmware loading and recovery

Decide how an assembled board with blank firmware will receive its first program. Then decide how you will recover it after loading a faulty application. Include the connector or test pads, required adapter, reset access and programming instructions in the design brief.

If you keep the same development board, its existing workflow may remain usable, provided the enclosure leaves access. If you integrate the microcontroller, ask the engineer to review the programming and boot requirements for that exact device. Do not assume the familiar USB socket and upload behavior will follow automatically.

The handoff should identify who supplies any bootloader and test firmware, who performs initial programming, and how the firmware revision is recorded. Ask for a demonstrated loading procedure during acceptance. “Firmware supplied” and “firmware successfully loaded on every board” describe different deliverables.

## Review the physical assembly with the cables attached

Provide an enclosure drawing with mounting-hole positions and connector openings. Include cable direction, plug dimensions and space needed to insert or remove each connector. Check whether the programming cable can still reach the board when it is mounted.

Choose connector part numbers before approving the layout. Replacing a temporary header with a locking connector changes more than its label: the footprint, mating cable and assembly method must agree. Record which parts arrive on the PCB and which the user attaches later.

Request an [engineer review](/blog/pcb-engineer-review) of the schematic, layout and BOM together. Keep the working Arduino prototype available as a behavioral reference, with its firmware unchanged, until you can compare it against the new board.

## Define the first-board acceptance checks

Write down what you will compare: successful programming, startup, each connected peripheral and the intended user action. Where a result is measured, define a limit and method. Where it is a sequence, describe the input and expected output.

For a hypothetical sensor interface, a check might require the selected sensor to identify itself and produce a timestamped reading through the agreed debug connection. That is a proposed communication check, not evidence of measurement accuracy or a completed test. A [written prototype test plan](/blog/pcb-prototype-testing) should distinguish those claims.

Before ordering, confirm whether the selected architecture fits the [Proto Kit scope](/pricing). Keeping a module or development board does not automatically fit the component allowance, assembly limits or mechanical constraints. Review the complete BOM and the parts supplied by each party.

## Questions about Arduino to custom PCB projects

### Can I keep using my existing sketch?

Possibly, if the processor, board configuration, pin assignments and peripherals remain compatible. Confirm those assumptions and test the actual build. A working sketch on the original hardware is not proof that a changed board will run it unchanged.

### Do I have to remove the Arduino board immediately?

No. A shield or carrier can retain it while replacing the wiring and connectors. Choose full integration when your mechanical or functional requirements justify the additional design and validation work.

### Does a free preview include files I can send to a factory?

Ohmbo provides one free online design preview per account. Physical boards and downloadable design or manufacturing files are not included. Downloads become available after payment confirmation and order release.

## Prepare the handoff

An Arduino to custom PCB project is ready for review when you can name the architecture, map every used signal, load firmware and describe acceptance. Send those decisions with your working setup and enclosure constraints through the [prototype inquiry form](/contact). The engineer can then review the proposed board against the prototype you already understand.