ESP32 DevKitC V4

ESP32-DevKitC V4 is designed by the original ESP32 manufacturer Espressif. This board is suitable for experimenting with all ESP32 features as most of the I/O pins are broken out to the pin headers on both sides for easy interfacing. It comes with a decent voltage regulator and is available with a wide variety of original ESP32 modules, including the popular WROOM 32D (with PCB antenna) and WROOM 32U (with IPX-connector to connect an external antenna).

For Experienced Users

This development board is not a first choice for beginners:

• Drivers: driver installation may be required before the board is recognized by your computer because the board is not using one of the standard USB-to-Serial chips
• No LED: the board has no built-in LED that can be useful for testing and beginner sketches.
• Firmware Upload: Boot has to be pressed while Reset is pushed to manually switch the board to firmware upload mode.
• Breadboard: the development board cannot be placed on one standard breadboard due to its size.
• Pin Labels: the pins are labeled on the development board but the labels are hard to read.
• Unsafe Pins: since this development board exposes almost all microcontroller pins, some of the exposed pins cannot be used as GPIOs (because they are used internally for crucial components like external flash memory communications). Naively using these pins can lead to unexpected results.

Hardware Overview

The ESP32 module (depending on type either with attached PCB antenna, or with an IPX antenna jack) takes up half of the PCB surface area. Towards the inner side, there is unused space unless your breakout board uses the larger WROVER module with additional PSRAM.

USB Connector

On the opposite side, a Micro-USB connector lets you connect the board to a computer.

Behind the USB connector, a Silicon Labs CP2102 chip provides the USB to UART bridge at speeds of up to 3Mbps. This chip may require manual driver installation before it will be recognized by your computer.

Power Supply

The board provides three mutually exclusive ways to power it:

• USB: 5V USB is used and converted internally to 3.3V
• 5V/GND Pins: You can power the board through an external power supply by connecting it to the pins 5V and GND. The input power goes through the voltage regulator (like USB option).
• 3.3V/GND Pins: You can provide 3.3V directly by connecting a suitable power supply to the pins 3.3V and GND. These pins power the microcontroller directly and do not go through a voltage regulator. This option provides the best energy efficiency but is also the most dangerous one: if your external power supply does not always deliver regulated voltage in the range of 3.0-3.6V, the board and/or microcontroller will be damaged.

Always use only one of the three power methods listed above. When you power the board through an external power supply, never also supply power through USB. The most common error is to keep the board supplied by an external power supply while connecting it via USB cable to a computer in order to upload new firmware. Always make sure you either disconnect the external power supply, or you use a USB connector where the power lines can be turned off.

Voltage Regulator

Behind the CP2102, there is a IRU1117-33 3.3V voltage regulator capable of supplying 800mA. This regulator is used when you supply voltage either via USB or directly via the 5V pin. The voltage regulator accepts an absolute maximum input voltage of 7V.

On the right side, there are two JY3/S8050 epitaxal planar transistors with a high collector current of 500mA each and high total power dissipation.

Power LED

On the opposite side, a SMD power LED is located. It turns on whenever input power passes through the voltage regulator. It does not turn on when you supply 3.3V directly to the 3.3V pin.

The power LED is only on when the internal voltage regulator is used (when 5V are supplied). When powering via the 3.3V Pin, the power LED stays off to conserve energy in battery-operated scenarios.

Firmware Download Mode

The board comes with two push buttons labeled EN (reset button) and Boot.

To reliably put the board in Firmware download mode, hold down Boot and then press EN. The board is now ready to download new firmware via the USB connector. This needs to be done exactly at the point when the IDE is trying to connect to the board (not earlier).

Important: once the new firmware is successfully transferred to the board, press EN (reset) to leave the Firmware download mode and run your sketch.

Pinouts

This breakout board exposes most ESP32 pins:

The tables below provide detailed information for each header pin. The Pin Type resolves as follows: Power supply, Ground, Input, Output.

Header Pin Row 1

Header Pin Row 2

Pins To Avoid

Some pins are used internally for communication between ESP32 and SPI flash memory. They are grouped on both sides near the USB connector. Avoid using these pins, as it may disrupt access to the SPI flash memory/SPI RAM:

D0-D3, CMD, and CLK

Pins GPIO16 and GPIO17 are used internally by ESP32-WROVER. If you use the more commonly ESP32-WROOM, you are free to use these pins.

Issue On External Power

When this board is powered externally, it may not run the sketch immediately but requires the button EN to be pressed. Only then will the sketch run. The issue does not occur when the board is powered via USB.

The reason for this unwanted behavior is a capacitor (C15) connected in parallel to the Boot button. On newer versions of this breakout board, the capacitor meanwhile has been removed.

The picture shows a newer version with the solder pads for C15 (but with no capacitor present):

Only relatively old boards have this capacitor in place. If you do find a capacitor at this location and suffer from the issue, remove the capacitor manually.

The SMD capacitor is very small, and there are delicate tracks behind it that can easily be damaged by brute force or an over-sized and over-heated soldering iron. Desoldering this component requires proper tools (i.e. a heat gun).

Practical Considerations

This board is a development board in its best sense: it exposes almost all ESP32 pins and invites anyone to fully test-drive the ESP32.

Unfortunately, for the same reasons, the board is fairly large. Its width is 28mm which is unfortunately too wide to place the breakout board on the typical breadboards:

Only one row of header pins would remain accessible.

One Breadboard Isn’t Enough

Most breadboards are modular and can be combined and rearranged. When you take two breadboards and remove one powerrail each, you can stick them together in a way that provides the necessary real estate to place the breakout board:

Make sure you ground yourself before fiddling too much with the board trying to place it. Almost all microcontroller breakout boards are sensitive towards static electricity and can be accidentally destroyed by a single static spark.

Challenging: Working With The Board

Working with the DevKitC V4 isn’t as intuitive as with other boards.

No Builtin LED

For one, it does not have a built-in user-controllable LED, so simple blink sketches to verify the setup will not work.

There is a LED on the board, however this is the power LED that is not user-controllable.

No Dedicated Board Definition

Second, neither Arduino IDE nor platformio provide a dedicated board DevKitC V4, so you need to find a similar board youself. That’s no rocket science but also not trivial, especially for novice users.

In platformio, I opted for AZ-Delivery-Devkit-V4 (as some of the boards I used were indeed purchased at AZ-Delivery before I noticed that the same boards are available at a fraction of the price at AliExpress).

Most likely, the generic board esp32dev would have as well worked just fine.

This is platformio.ini I successfully used for testing:

[env:az-delivery-devkit-v4]
platform = espressif32
board = az-delivery-devkit-v4
framework = arduino

Make sure you remove any build flags or other settings that you do not positively know are necessary. If you copy&paste extra settings from other boards, you may easily run into compile exceptions like “Serial was not declared in this scope”.

In Arduino IDE, the generic board ESP-WROOM-32 seems like a reasonable choice.

Manual Driver Installation Required

Worst, the board may not even be recognized by your computer when you plug it in via a USB cable.

This is due to the USB to UART bridge used by this board: the CP2102 from Silicon Labs is powerful - but not as ubiquous as i.e. the CH340.

Thus, it may require a manual driver installation.

Is Board Recognized When USB-Connected?

The first step in diagnosing issues is to check whether the board gets recognized by the computer when you plug in its USB cable. If a new device discovered sound plays, that’s a good indicator. However, do make sure whether there is indeed a new COM Port visible in device manager (on Windows).

Install Drivers Manually

If no COM Port appears in device manager when you connect the board to the computer, then most likely the CP210x drivers are missing.

Visit Silicon Labs and download the appropriate driver package. On Windows, I installed CP210x Windows Drivers and CP210x VCP Windows.

Once you downloaded the driver packages, make sure you right-click the downloaded ZIP file, choose Properties, and click on the button to unblock the file before you unzip it.

Once drivers are installed, restart the computer. When you now connect the board, it should be correctly recognized, and a COM port should appear in device manager.

If things still do not work, make sure you use an appropriate USB cable. Try using a cable that you previously successfully used to upload firmware. There are plenty of cheap cables with no data wire connection, high cable resistance, or loose plug connections.

Button Press Required To Upload Sketch

If you managed to successfully connect the board to your computer, then there is a final challenge to master: the board needs to be set to firmware download mode at just the right moment in time.

When you upload a new sketch, your IDE by now should be able to identify a COM port at which the board is to be found.

The IDE next tries to connect to the board - which will fail if you don’t manually intervene:

As soon as the IDE starts trying to connect to the board, hold the Boot button and press EN shortly. This procedure enables the firmware download mode. Only now will the board respond to the connection requests.

The connecting… message will now hold for a second, and then the IDE starts to upload the new sketch to the board.

Conclusion

The DevKitC V4 is a great development board to test-drive ESP32 features simply because it exposes all important CPU pins.

Solid

It’s solidly made with a good voltage regulator, and its street price of under EUR 2.00 is ok, too (don’t buy it for EUR 12.00 or more - there are still people selling it for prices like this).

But, but, but…

There are a lot of down-sides, though, which make this board definitely not a recommendation for novices or anyone focusing on convenience:

• USB to UART component apparently requiring manual driver install
• Cumbersome procedure to enable firmware download mode
• hard-to-read and somewhat confusing pin labels on PCB
• no internal LED (which is just very convenient for simple checks and balances)
• wide form factor that makes it impossible to plug the board into a single standard breadboard.

Materials

Board Schematics
ESP32 Datasheet
CP2102 USB-UART-Bridge
IRU1117 3.3V Voltage Regulator
S3050/J3Y Transistor

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