Provisioning requires that you at least once upload ESPHome firmware via USB cable. After this succeeds, you then use wireless OTA to upload any future firmware updates. All USB and button-press hassles are then a thing from the past.
Which is why it is extremely frustrating when the ESP Web Tool does not work with your microcontroller board, and you just can’t get the initial ESPHome firmware update done via USB.
ESP32 S2 Mini is a popular example for a board that cannot be provisioned by ESPHome (because of its strange USB implementation). With the steps below, you get it done anyway. Thanks to the new ESPHome firmware and its wireless updates, you heal its USB woes as in the future you no longer need USB firmware upload mode.
Quick Overview
Connecting and uploading new firmware via USB cables is technically challenging: it may work flawlessly with one microcontroller type, and may as well cause a plethora of frustrating issues and error messages with another.
Why USB Communications Is So Prone To Errors
Communication via USB is technically not strictly standardized: a variety of techniques exist by which microcontrollers and boards can transfer information via USB:
- Native USB support: newer microcontrollers come with native USB support built-in. However, there are different levels of native USB support.
- USB OTG (On-The-Go): found in ESP32-S2 and ESP32-S3
- USB Serial/JTAG: found in ESP32-C3
- UART Chips: microcontrollers lacking native USB support use separate UART chips on the microcontroller boards. There are many different UART chip families, and they require specialized drivers on your PC that may or may not be part of the OS. Some require separate driver installation.
What makes matters worse is that firmware updates via USB require the microcontroller to enter a special firmware upload mode. Some boards switch to this mode automatically, some switch sometimes automatically, and some require the boot switch to be pressed during a reset.
As if that wasn’t enough, some microcontroller boards like ESP32 S2 Mini actually change USB port when switching from normal mode to firmware upload mode, breaking the connection to tools like the ESPHome Web Tool that are not expecting this.
More Robust Tools To The Rescue
Adafruit ESP Tool works reliably with ESP32 S2 Mini and many other similarly affected microcontroller boards. It runs right inside your browser, just like ESPHome Web Tools: both tools use the same web serial connection inside the browser and require a compatible browser, i.e. Chrome. Once connected to a microcontroller, this is what the tools look like:
Firmware File Required
Both tools essentially do the same thing: they upload a binary firmware file to a microcontroller.
ESPHome Web Tool differs a bit in that it optionally supports the function Prepare for first use which in the background downloads a generic ESPHome firmware file for you. Adafruit ESP Tool always wants you to provide the firmware file(s) to upload.
Here are the two options you have:
- Generic Provisioning: to mimick the Prepare for first use functionality and provision a microcontroller in a way that it can later be adopted by ESPHome, download the generic firmware file that ESP Web Tool uses.
- Configuration: to mimick the Install functionality and upload a newly created firmware file that works just for one particular microcontroller, create a dedicated ESPHome configuration, let ESPHome then create a firmware file for it, and download the file to your computer.
Either way, you get a firmware file that Adafruit ESP Tool can upload to your microcontroller. Here are the step-by-step instructions to create the binary firmware files for both approaches:
Downloading Generic Firmware File (aka Prepare for first use in ESPHome Web Tool)
The default firmware file that is used by Prepare For First Use in ESPHome Web Tool is not officially advertised as a separate download. ESPHome Web Tool loads it from a non-public url that can change without notice.
These are the firmware files I used for various microcontroller types, downloadable as zip-files that need to be unpacked before use:
| Microcontroller | Generic ESPHome Provisioning Firmware File (zip) | Original Size (KB) |
|---|---|---|
| ESP8266 | esphome-web-esp8266.factory.bin | 418 |
| ESP32 | esphome-web-esp32.factory.bin | 1.602 |
| ESP32-S2 | esphome-web-esp32s2.factory.bin | 864 |
| ESP32-S3 | esphome-web-esp32s3.factory.bin | 1.365 |
| ESP32-C3 | esphome-web-esp32c3.factory.bin | 1.516 |
Make sure you download and use the firmware file for the microcontroller type you are using.
Firmware files for microcontrollers without bluetooth support (ESP8266 and ESP32-S2) do not include Improv-BLE (WiFi configuration via bluetooth). Their firmware file sizes are considerably smaller.
Those firmware files may be stale by the time you read this: they are based on ESPHome 2026.6.6. That’s not really a problem as you update to the latest ESPHome version anyway when you later adopt the provisioned device into your ESPHome Dashboard.
However, you can try and use the original urls, hoping that they still work and meanwhile point to a more recent version of the firmware file:
| Microcontroller | Original Firmware Download Urls for Prepare for first use |
|---|---|
| ESP8266 | https://firmware.esphome.io/esphome-web/24.8.3/esphome-web-esp8266.factory.bin |
| ESP32 | https://firmware.esphome.io/esphome-web/24.8.3/esphome-web-esp32.factory.bin |
| ESP32-S2 | https://firmware.esphome.io/esphome-web/24.8.3/esphome-web-esp32s2.factory.bin |
| ESP32-S3 | https://firmware.esphome.io/esphome-web/24.8.3/esphome-web-esp32s3.factory.bin |
| ESP32-C3 | https://firmware.esphome.io/esphome-web/24.8.3/esphome-web-esp32c3.factory.bin |
Or, you figure out the url that ESPHome Web Tool is using right now: follow the same procedure I originally used. This guarantees that you work with the latest firmware file and get exactly the same results that you would get by using the ESPHome Web Tool today:
- Open the ESPHome Web Tool in your browser.
- Connect a supported microcontroller to your computer via USB cable (i.e. ESP32 or ESP32-C3). Do not connect the problematic microcontroller.
- Once ESPHome Web Tool is connected, on the web page, right-click the button PREPARE FOR FIRST USE. A context menu opens. Click Inspect.
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This opens the browser developer tools. Click the tab Network.
- Now, normal-click PREPARE FOR FIRST USE to actually start the firmware upload.
- In the Network tab, you see the urls from which the tool downloads files. The list contains a bunch of javascript files plus the binary firmware file you are after. It carries the extension .bin:
- When you hover over its entry or click it with the right mouse button, you see the full url and can open it in a separate browser tab (which essentially downloads it).
The firmware files are specific for a given microcontroller type, so if you connected an ESP32-C3, you figured out the download url for the firmware file that works for this microcontroller type only. Simply compare the url you figured out with the table of download urls I figured out a while ago (see above). If your url matches the one in the table, then they apparently haven’t changed, and you can simply use the url in the table that matches your microcontroller type.
If however the url differs from the ones in the table, then apparently the url structure or general download location has changed. In this case, simply try and adjust the url you just figured out to make it point to the firmware file for the microcontroller type you need: replace any instance of microcontroller type, i.e. c3, in the url you just figured out, with the required type, i.e. s2. Note that the microcontroller type may appear more than once in the url. Replace all occurances. This way, you get the url for the microcontroller you need.
Maybe there are easier ways to get these files, and possibly they are even part of a public repository. I searched for many hours without luck. If you find a better way, please leave a comment below.
Creating Firmware File For One Specific Microcontroller (aka Install in ESPHome Web Tool)
If you deal with just a single microcontroller and would like to immediately put it to work, then this is what you do to create the firmware file:
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In ESPHome Dashboard, click New Device, and create a new configuration. Make sure you specify ESP32-S2 as device type.
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Once you created the configuration, click its three-dot menu, choose Install, then click Manual download.
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Choose factory format as file format, and download the firmware file to your computer.
The firmware file you just created can only be used on one microcontroller. Do not upload it to a bulk of microcontrollers. Since the firmware is already customized (including the device name), you would clone microcontrollers and get into trouble with multiple microcontrollers using the same mDNS name and the same API keys.
Uploading Firmware
Once you have the firmware file at hand - either the generic one, or a hand-tailored that you created via a specific configuration - you can now upload it to your microcontroller.
If you choose to upload the generic ESPHome firmware file that you downloaded from firmware.esphome.io, make sure you are selecting the firmware file for your microcontroller type! If you accidentally upload the firmware made for ESP32-S3 to a ESP32-S2, then the microcontroller will no longer respond. Since ESP microcontrollers have a write-protected boot loader, you can simply repeat the steps and upload the correct firmware file to fix this. You cannot brick ESP microcontrollers.
Open the Adafruit ESP Tool in your browser:
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Connect the microcontroller via USB cable to your computer. Hold its boot button while pressing reset to force it into firmware upload mode.
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In your browser, navigate to the Adafruit ESP Tool. In its upper right corner, click Connect.
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Select the microcontroller in the dialog, and click Connect. If the tool reports that no compatible device was found, make sure you enabled the firmware upload mode on the microcontroller: hold its boot button while you press its reset button.
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Once connected, in the lower part of the window, click Erase to erase the memory. This may take a few seconds, and there are no progress indicators. The black terminal window tells you when the erase process has completed.
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Click the top-most Choose file button, then select the firmware file you created and downloaded. Click Program.
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The firmware is transferred to your microcontroller. A progress bar shows the status.
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Once the firmware has been transferred, click Disconnect, and only then press the reset button on your microcontroller board to make sure it boots from the newly uploaded firmware.
Configure WiFi Access
If you used the default provisioning firmware that you downloaded from esphome.io, the device does not yet know how to connect to your WiFi. You need to tell the device the WiFi SSID and WiFi password before it can go online and be discovered by ESPHome.
Part of the default ESPHome provisioning firmware is improv_serial (improv via BLE is not available with the ESP32 S2 as it does not support bluetooth).
Improv_serial allows you to connect the device via USB cable and ESPHome Web Tool, then configure its WiFi in your browser.
The default provisioning process using [ESPHome Web Tool]ESPHome Web Tool failed for your particular microcontroller (which is why you are on this page). Fortunately, Improv uses the default USB Port and not the secondary USB Port that becomes active in firmware upload mode. So the ESPHome Web Tool works just fine - even with problematic boards like ESP32 S2 Mini - once a microcontroller is running ESPHome firmware.
You can configure WiFi now (and complete the provisioning process), or do it later at any time. It just needs to be done before you can see and adopt the microcontroller into ESPHome.
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Connect the microcontroller via USB cable to your computer. Do not enable firmware update mode. If in doubt, press the reset button once.
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Make sure you closed all other tools (i.e. the Adafruit flasher). Then open the ESPHome Web Tool in your browser.
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Click CONNECT, and select the microcontroller in the dialog. A ESP32 S2 Mini should show as TinyUSB in this list. If you instead see ESP32-S2, then the microcontroller is in firmware upload mode. In this case press its reset button to return to normal mode.
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Once connected, click the three dot menu and choose Configure Wi-Fi.
- A dialog opens. Note the temporary device name (i.e. esphome-web-8b87ca). With this name will the device surface in ESPHome Dashboard once you configured WiFi.
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Click CONNECT TO WI-FI, select the WiFi SSID you want to connect to, and click CONNECT. After a few seconds, you get a confirmation that the device is now fully configured.
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Click CLOSE, then click the three-dot menu, and choose Disconnect.
If you can connect to your microcontroller, but once you click Configure Wi-Fi, you get an error message stating that Improv Wi-Fi Serial was not detected, then you either connected the microcontroller in firmware upload mode (press its reset button, and try again), or you uploaded a wrong firmware file that was made for a different microcontroller type (repeat the provisioning with the correct firmware file).
Flood Of Discovered Devices
If you provision a bunch of microcontrollers this way, whenever you configure its WiFi, the connection is automatically tested, so the devices go online and connect to your WiFi.
Even if you turn them off and put them in a drawer immediately after the provisioning process has completed, ESPHome may have already picked up the provisioned devices, and the ESPHome Dashboard is filling with discovered devices that are ready to adopt.
Don’t worry though: once a discovered device goes online, after a grace period ESPHome automatically removes its tile again from the dashboard.
Typically, newly provisioned devices surface with their cryptic temporary name in ESPHome dashboard. If however you adopted this device before - even if you have meanwhile deleted it from ESPHome - it pops up again with the last name that was assigned to it. That’s because ESPHome identifies new devices by their MAC address - which doesn’t change.
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(content created Jun 02, 2024 - last updated Jul 12, 2024)