Concept renderAn ESP32 dev board is a lab tool. It adds a USB-to-UART bridge, an auto-reset circuit, buttons, headers and a USB-sized power path. A product board replaces those with a battery power design, test pads for flashing, fixed strapping pin states, an antenna placed at the board edge, and security settings burned into eFuses.
Most connected devices start as a demo on an ESP32 dev board. The board is a microcontroller board built for a desk: plug in USB, flash, and wire sensors to the headers. Turning that demo into a product means removing what only helps development and designing what the dev board never had to solve. This guide walks through each change using Espressif's own design guides and datasheets.
This is an engineering summary for the original ESP32 and the ESP32-WROOM-32E module. Other ESP32 chips have different pins and rules, so read the guide for your exact chip. All sources were read on November 12, 2026.
What does an ESP32 dev board hide that a product board must handle?
Espressif's ESP32-DevKitC V4 is a typical ESP32 development board. Its guide lists an ESP32-WROOM-32E module, a USB-to-UART bridge with transfer rates up to 3 Mbps, a Boot button, an EN reset button, a power LED and pin headers. Power comes from the Micro USB port, the 5V pin or the 3V3 pin, and the guide warns to use only one at a time (DevKitC V4 user guide, as of November 2026). The table maps each dev board feature to the product decision it hides. The product column is engineering reasoning.
| Dev board part | What it does on the desk | What the product board needs |
|---|---|---|
| USB-to-UART bridge | A bridge chip turns USB into the serial port used for flashing and logs. | Decide whether the product keeps a USB port at all. Many keep only test pads for UART0. |
| Auto-reset circuit | Two transistors let esptool drive EN and GPIO0 from the DTR and RTS lines, so flashing needs no button presses. | Replace it with test pads and a fixture that drives EN and GPIO0, or keep a minimal version for development boards only. |
| Boot and EN buttons | Boot pulls GPIO0 low. EN resets the chip. | Keep EN and GPIO0 reachable on pads. Add a user button only if the product needs one. |
| Power from USB | The board runs from the USB port, the 5V pin or the 3V3 pin, one at a time. | Design the battery, charger and regulator path for the real current peaks and sleep current. |
| Pin headers | Most module pins are broken out for jumper wires. | Route only the pins you use. Keep strapping pins in a known state at reset. |
| Module antenna placement | The module antenna sits at the board edge with nothing around it. | Place the antenna at the edge of your own board and leave clearance inside the housing. |
The esptool documentation describes the auto-reset circuit: esptool asserts DTR and RTS on the USB-to-serial chip, which connect to GPIO0 and EN, and a two-transistor circuit stops the chip from resetting when both lines are asserted together (esptool boot mode selection, as of November 2026). A product can drop all of this. The factory still needs a way to reach those two pins.
How does the power design change for a battery product?
On a dev board, USB supplies plenty of current and nobody counts microamps. A battery product has to handle both ends: the transmit peak and the sleep floor.
Peak current
Espressif recommends a 3.3 V supply with output current of no less than 500 mA when a single supply is used. It also suggests an ESD protection diode and at least 10 µF at the main power entrance (ESP32 schematic checklist, as of November 2026). The ESP32 datasheet lists a typical 240 mA while transmitting 802.11b at +19.5 dBm, and 130 mA for Bluetooth at 0 dBm (ESP32 datasheet v5.3, as of November 2026). The WROOM-32E module datasheet gives an operating range of 3.0 V to 3.6 V and a minimum of 0.5 A from the external supply (WROOM-32E datasheet v2.1, as of November 2026).
A single-cell lithium battery sits around 3.7 V and falls as it discharges. The regulator must hold the module above 3.0 V during transmit peaks when the battery is low. The WROOM-32E datasheet lists 239 mA average and 379 mA peak for 802.11b at 19.5 dBm, measured with a 3.3 V supply (WROOM-32E datasheet v2.1, as of November 2026). Size the supply for that peak and for the 0.5 A minimum the same datasheet asks for. The 240 mA chip figure above is a typical value, so it is too low for sizing. That sets the regulator type and the cutoff voltage. Our LDO vs buck converter guide covers the tradeoff, and our LiPo vs Li-ion battery guide covers the cell.
Sleep current
The ESP32 datasheet lists 10 µA in Deep-sleep with the RTC timer and RTC memory on, 5 µA in Hibernation with only the RTC timer, and 1 µA with CHIP_PU held low (ESP32 datasheet v5.3, as of November 2026). Those are chip figures. On a dev board, the bridge chip, power LED and regulator quiescent current add to them, so a dev board sleep measurement says little about the product. Measure sleep current again on the first custom board. For measuring sleep current and radio bursts, see How to Measure Sleep Current on Microamp Devices.
What do the strapping pins and reset circuit do?
At each startup or reset, the ESP32 reads a few pins to decide how to boot. Espressif lists GPIO0, GPIO2, GPIO5, MTDI and MTDO as strapping pins. After reset they work as normal pins (ESP32 schematic checklist, as of November 2026). The esptool guide explains what they do (esptool boot mode selection, as of November 2026):
- GPIO0. Held low at reset, the chip enters the serial bootloader. High, it runs from flash. It has an internal pull-up.
- GPIO2. Must be floating or low to enter the serial bootloader.
- MTDI (GPIO12). If driven high, flash voltage switches to 1.8 V. With 3.3 V flash, that can stop the board from flashing or booting.
- MTDO (GPIO15). Driven low, it silences the ROM boot messages.
On a dev board these pins are free. On a product, a sensor, LED or button may sit on one of them and pull it the wrong way at reset. Check the state of every strapping pin at power-up, including what connected parts do before firmware runs.
The reset pin needs care too. Espressif says CHIP_PU (EN) must not be left floating and recommends an RC delay, usually 10 kΩ and 1 µF, so the chip enables after the 3.3 V rails settle. For unstable supplies, it suggests a power monitor chip with a threshold around 3.0 V (ESP32 schematic checklist, as of November 2026).
Module or chip-down: which path fits your product?
The dev board uses a module: the ESP32 chip, flash, crystal, RF matching and antenna under one shield. A custom board can keep a module or place the chip directly on the board.
Keeping a module
The WROOM-32E comes with 4, 8 or 16 MB of flash, an on-board PCB antenna (or an external antenna connector on the WROOM-32UE) and lists RF certificates for the module (WROOM-32E datasheet v2.1, as of November 2026). A module helps with FCC work because the transmitter can carry its own modular grant. Under 47 CFR 15.212, a modular transmitter needs its own shielding, buffered data inputs, its own power supply regulation, and an antenna that is permanently attached or uses a unique connector. If the module's FCC ID is not visible after installation, the host must carry a label such as "Contains FCC ID" (eCFR 15.212, as of November 2026). The finished product still needs its own testing. Our guide to pre-certified modules and FCC explains what a module grant does and does not cover.
Going chip-down
Placing the chip directly saves space and can lower unit cost at volume, but it moves the RF work to your team. Espressif notes that the integrated circuitry needs only 20 electrical components, a crystal and an SPI flash. It also says RF matching values vary with the board, so the values in Espressif modules cannot be applied directly, and it gives a tuning procedure with a network analyzer. The firmware supports only a 40 MHz crystal, with accuracy within ±10 ppm (ESP32 schematic checklist, as of November 2026). A chip-down radio also needs its own full FCC certification.
For flash and PSRAM on a chip-down design, Espressif recommends models it has validated and zero-ohm resistor footprints in series on the SPI lines (ESP32 schematic checklist, as of November 2026).
Where should the antenna go on the product board?
Espressif recommends placing a module's PCB antenna outside the base board, with the feed point near the board edge. If the antenna cannot extend past the edge, cut the base board on both sides of and below the antenna, and do not place the module in the middle of the board with a hollow cut around it. Inside the housing, it recommends at least 15 mm of clearance around the antenna in all directions, and testing throughput and range in the final product (ESP32 PCB layout design, as of November 2026).
Fifteen millimeters is hard to find in a small device. Batteries, screws, metal trim and the user's hand all sit close. Decide early what gives: board shape, battery position or antenna type. Our guide to PCB antenna design for small devices covers the options.
How do you flash and test boards in production?
The factory needs to load firmware, write any per-device data and test each board without a USB bridge. A common approach is a pogo-pin fixture on test pads. Plan the pads before layout:
- 3V3 and GND, so the fixture can power the board without the battery.
- EN and GPIO0, so the fixture can reset into the serial bootloader.
- U0TXD and U0RXD. UART0 is the default port for download and log output. Espressif recommends a 499 Ω series resistor on U0TXD to suppress harmonics (ESP32 schematic checklist, as of November 2026).
- Any test points the functional test needs, such as the battery rail and sensor supply.
If you keep the auto-reset circuit on a development variant, the esptool guide says a 1 µF to 10 µF capacitor between EN and GND is needed for it to work reliably (esptool boot mode selection, as of November 2026). For how fixtures and test stages fit together, see in-circuit test vs functional test.
Which security settings must be set before the product ships?
A dev board leaves the flash readable and accepts any firmware. A product usually should not. Two ESP32 features handle this. Both depend on eFuse settings, and some of those settings are permanent, so test the full sequence on spare boards first.
- Flash encryption. Firmware is flashed as plaintext and encrypted in place on first boot, so reading the flash chip does not recover most contents. Espressif says production use should enable flash encryption in Release mode only. In Development mode, new plaintext firmware can still be flashed, which indirectly allows reading the plaintext (ESP-IDF flash encryption, as of November 2026).
- Secure Boot v2. The bootloader checks an RSA signature before it runs an image. On the original ESP32, Secure Boot v2 needs chip revision v3.0 or later. Espressif recommends using secure boot and flash encryption together, because secure boot alone allows a time-of-check to time-of-use attack (ESP-IDF Secure Boot v2, as of November 2026).
- UART download mode. The same page recommends disabling UART ROM download mode for better security. Decide how field units will be updated before you do this.
Plan who holds the signing keys and how OTA images are signed. Our guide to secure boot and signed firmware for small devices covers the process.
What should you check before ordering the first custom board?
Bring these questions to the schematic review.
- Module or chip-down, and which FCC path does that choice set up?
- Which flash size and PSRAM option does the firmware need, with room for two OTA images?
- What is the peak current during Wi-Fi transmit, and does the regulator hold 3.0 V at that peak with a low battery?
- What state does each strapping pin see at reset, including any sensor or button connected to it?
- Is there an RC delay on EN, and does it meet the power-up timing in the guide?
- Which pads does the production fixture use for power, EN, GPIO0, U0TXD and U0RXD?
- When are flash encryption and secure boot enabled, and in which mode do boards leave the factory?
- Where does the antenna sit in the housing, and what metal is within 15 mm of it?
For how a full PCB project runs from requirements to bring-up, see our PCB design process guide. The PCB prototype gate shows where the first custom board fits in a Duobay project.
Questions about moving from an ESP32 dev board
Can I use an ESP32 dev board inside my product?
For a few prototypes or a lab tool, sometimes. For a product, it usually costs space, battery life and certification effort. The dev board keeps a USB bridge, a power LED and headers powered or in place, and its shape rarely fits a housing. A custom board keeps only the parts the product needs.
Is the ESP32-WROOM-32 development board design ready for production?
The development board shows a working reference, but its power path, reset circuit and connectors are chosen for a desk. Espressif's DevKitC V4 guide even notes that capacitor C15 on earlier boards may make the board boot into Download mode (DevKitC user guide, as of November 2026). Use the hardware design guidelines as the source for your own schematic.
Does using a certified ESP32 module mean my product needs no FCC testing?
No. A module grant covers the module's transmitter under the conditions in its grant. 47 CFR 15.212 lists what a modular transmitter must have, including its own shielding, power supply regulation and a permanently attached or unique antenna (eCFR 15.212, as of November 2026). The finished product still needs its own compliance work. See what FCC certification covers.
Which ESP32 should I choose for a new product?
It depends on the radios, power and memory the product needs. The original ESP32 has Wi-Fi and Bluetooth Classic plus Bluetooth LE. Newer chips trade some features for lower power or newer radios. Our ESP32-C3 vs C6 vs S3 comparison covers the newer parts.
How can Duobay help turn an ESP32 prototype into a product?
Duobay develops custom devices with a Shenzhen engineering team that covers electronics, firmware, enclosure, app and test, and builds samples and small batches. Firmware source and the SBOM are delivered to you, and source files are assigned to you at every paid gate. Initial calls are free, and we do not publish prices. Tell us about your device.
If you have an ESP32 demo and want it turned into a product board, tell us about your device.
Sources. All pages accessed November 12, 2026. Espressif updates its guides often, so re-read the current version for your chip.
- Espressif, ESP32-DevKitC V4 user guide (link)
- Espressif, ESP32 Hardware Design Guidelines, schematic checklist (link)
- Espressif, ESP32 Hardware Design Guidelines, PCB layout design (link)
- Espressif, esptool, boot mode selection for ESP32 (link)
- Espressif, ESP-IDF, Secure Boot v2 for ESP32 (link)
- Espressif, ESP-IDF, flash encryption for ESP32 (link)
- Espressif, ESP32-WROOM-32E and ESP32-WROOM-32UE datasheet, version 2.1 (link)
- Espressif, ESP32 series datasheet, version 5.3 (link)
- eCFR, 47 CFR 15.212 Modular transmitters (link)
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