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51 lines
2.8 KiB
ReStructuredText
51 lines
2.8 KiB
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Using an ESP devboard as a USB-UART bridge
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==========================================
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.. _devboard-as-flasher:
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ESP development boards usually have an onboard USB interface, either built into the chip (e.g. ESP32-S3) or via an onboard USB-UART bridge chip.
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However some ESP based devices not designed for development work don't bother with this,
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and only expose the UART0 pins (TX and RX) for flashing purposes.
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Normally you would use a dedicated USB-UART interface board for this but what if you don't have one?
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In this "emergency" situation it is possible to use a development board that does have a USB-UART bridge chip to flash another device.
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This is achieved by holding the ESP chip in reset so that it doesn't interfere with the bridge chip operation.
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It does NOT require any firmware to be flashed onto the development board
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and will not change anything already flashed onto it - it's purely a way to use the serial interface chip.
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We will refer to the devboard with functional USB_UART bridge chip as flasher board for this guide.
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Make sure you've read the :doc:`/guides/physical_device_connection` for properly understanding the functionality of your flasher devboard.
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.. figure:: /guides/images/devboard-as-flasher.png
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:align: center
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:width: 75.0%
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Connection diagram for an ESP flash target
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You need to make the following electrical connections:
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.. note::
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- Most ESP32 S and C series boards do *not* have a separate USB-UART chip - they have it built into the ESP - so are not suitable for this application.
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- The 5V connection on either board may be labelled either ``5V`` or ``VIN``. Some boards may not have a 5V connection and will require 3.3V only.
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- Rather than powering the target board from the flasher board, it is also possible to use a separate power supply, just make sure all the ground pins are connected together.
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- connect both ``EN`` and ``GND`` together in the flasher devboard
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- ``+5.0V`` or ``3V3`` on the flasher devboard to ``VIN`` or ``3V3`` respectively of the target device
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- ``GND``, or ground of flasher devboard to ``GND`` of the target device
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- ``TX`` of flasher devboard to ``TX`` of the target device
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- ``RX`` of flasher devboard to ``RX`` of the target device
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Pulling down ``EN`` by connecting it to ``GND`` on the flasher board prevents
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the ESP chip on flasher module from booting and polluting the serial lines.
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.. note::
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- If the board has not previously had ESPHome loaded, you may need to pull the ``IO0`` pin low (i.e. connected to ``GND``) to force the board into flash mode.
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This must be done before power is applied.
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- Do not connect 3V3 to VIN of the target devices with a 3V3 LDO as it may lead to brownouts.
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Once the connections are made, plug the flasher board into your computer via USB and proceed with flashing the target board via whichever means you intend to use.
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