smôl ESP32 Hookup Guide

Contributors: PaulZC
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smôl is a new board format and, as the name suggests, they're really small!

smôl ESP32


The smôl ESP32 is a Processor Board for smôl, based on the excellent Espressif ESP32 processor.

Each smôl board measures just 1.60" by 0.42" (40.6mm by 10.7mm). We made the boards just wide enough so we could squeeze USB-C and 16-way Flexible Printed Circuit (FPC) connectors on there. Some of the boards have components on both top and bottom layers which again helps keep the boards small.

smôl boards are designed to stack one on top of the other, using 16-way 0.5mm-pitch FPCs to provide the interconnect from one board to the next. Each board has an IN FPC connector on the bottom layer and an OUT FPC connector on the top layer. The boards stack in a zig-zag daisy chain; signals and power are passed from one board to the next up and down the chain through the FPCs.

Required Materials

As a minimum, you're going to need a USB-C cable to connect your smôl ESP32 to your computer:

Reversible USB A to C Cable - 2m

Reversible USB A to C Cable - 2m

USB 3.1 Cable A to C - 3 Foot

USB 3.1 Cable A to C - 3 Foot


The ESP32 Processor Board is part of the smôl ecosystem. Why not pair it with one of the smôl Peripheral Boards?

smôl ARTIC R2


smôl ZOE-M8Q


To be able to reduce the sleep current below 10µA, you're going to want to pair the ESP32 with one of our intelligent smôl Power Boards:

smôl Power Board LiPo

smôl Power Board LiPo

smôl Power Board AAA

smôl Power Board AAA


Don't forget that you will need Flexible Printed Circuits to connect your smôl boards together. You're going to need one FPC per board. Our 36mm FPC is the perfect length if you want the smôl boards to stack neatly, one on top of the other.

smôl 36mm 16-way Flexible Printed Circuit


Need to do some prototyping with smôl? Or want to connect standard SPI or Qwiic (I2C) boards to your stack? The smôl Header is perfect for that:

smôl Header

smôl Header


Suggested Reading

This is the hookup guide for the smôl ESP32 Processor Board. Click the button below if you want to find out more about smôl itself.

We recommend taking a look through the following tutorials if you are not familiar with the concepts covered in them:

Serial Peripheral Interface (SPI)

SPI is commonly used to connect microcontrollers to peripherals such as sensors, shift registers, and SD cards.


An introduction to I2C, one of the main embedded communications protocols in use today.

Hardware Overview

In this section we'll cover what's included on the smôl ESP32 Processor Board.

Espressif ESP32

Ahhh, the Espressif ESP32. It's one of the most unique microcontrollers on the market. In it's native form, it has a laundry list of features. On the smôl Processor Board, we include the following:

  • Dual-core Tensilica LX6 microprocessor
  • Up to 240MHz clock frequency
  • 520kB internal SRAM
  • Integrated 802.11 B/G/N WiFi transceiver
  • Hardware accelerated encryption (AES, SHA2, ECC, RSA-4096)
  • 16MByte Flash Storage
  • Typical current draw: from USB (5V); using on-board regulator; CP210x active:
    • SimpleWiFiServer (receive): 64.7mA (AVG); 59.1mA (MIN); 144mA (MAX)
    • SPIFFS_Test (writing): 87.4mA (AVG)
    • Light sleep: 11.1mA (AVG)
    • Deep sleep: 9.6mA (AVG)
  • Typical current draw: from smôl 3.3V; on-board regulator disabled; CP210x inactive:
    • SimpleWiFiServer (receive): 63.6mA (AVG); 58.5mA (MIN); 142mA (MAX)
    • SPIFFS_Test (writing): 74.9mA (AVG)
    • Light sleep: 1.4mA (AVG)
    • Deep sleep: 450µA (AVG)
  • The sleep current can be reduced to less than 10µA by pairing the smôl ESP32 with one of our intelligent Power Boards

Espressif chip highlighted

WS2812C RGB Status LED

We've included a miniature WS2812C RGB LED for visual status feedback:

Status LED highlighted

Wireless Antenna

Need wireless? The Espressif chip provides a WiFi transceiver which sends and receives data through a 2.4GHz Antenna.

Wireless Antenna highlighted

USB-C Connector and CP210x USB Interface

The USB-C connector allows you to connect the smôl ESP32 to your computer for programming and diagnostics.

Important: If you've never connected a CP210x device to your computer before, you will need to install drivers for the USB-to-serial converter. Check out our section on How to Install CP2104 Drivers for help with the installation. If you try to use a default generic USB driver, automatic uploading from the Arduino IDE is likely to fail.

USB highlighted

FPC Connections

Like all of our smôl boards, the ESP32 Processor Board is equipped with two 16-way 0.5mm-pitch Flexible Printed Circuit connectors. FPCs are used to link the smôl boards together in a daisy-chain.

The pin-out for the smôl ESP32 is as follows:

FPC connections pin 1

Connector Pin No.Signal NameFunctionArduino Digital Pin No.
1PROC_PWR_ENProcessor Power EnableN/A
23V33.3V Power RailN/A
3GNDPower Ground / 0VN/A
4SCLKSPI Clock18
5COPISPI Controller Out Peripheral In23
6CIPOSPI Controller In Peripheral Out19
7CS0SPI Chip Select 05
8CS1SPI Chip Select 114
9CS2SPI Chip Select 213
10GPIO0General Purpose Input / Output 027
11GPIO1General Purpose Input / Output 126
12SDAI2C Data21
13SCLI2C Clock22
14GNDPower Ground / 0VN/A
153V33.3V Power RailN/A
16V_USBUSB Power Rail (5V)N/A

The IN and OUT pin connections are identical on the smôl ESP32. (That's not always true on smôl Peripheral Boards. Check the Peripheral Board Hookup Guide for full details.)

We use a technique called waterfalling on the SPI Chip Select and GPIO signals. If you haven't used waterfalling before, please check out the smôl Hookup Guide.

The smôl ESP32 has an on-board 3.3V regulator for stand-alone use, powered by 5V from the USB-C connector. The PROC_PWR_EN signal allows a smôl Power Board to disable the Processor Board regulator. Please see the smôl Hookup Guide for more details.

Software Setup and Programming

Note: All of the examples in this tutorial assume you are using the latest version of the Arduino IDE on your desktop. If this is your first time using Arduino, please review our tutorial on installing the Arduino IDE. If you have not previously installed an Arduino library, please check out our installation guide.
Important: If you've never connected a CP210x device to your computer before, you will need to install drivers for the USB-to-serial converter. Check out our section on How to Install CP2104 Drivers for help with the installation. If you try to use a default generic USB driver, automatic uploading from the Arduino IDE is likely to fail.

To get started with the smôl ESP32 Processor Board, you'll need to install the ESP32 Board Definition. Open the Arduino IDE (must be v1.8.13 or later) and navigate to File->Preferences, like so:

Arduino Preferences, under File

Having a hard time seeing? Click the image for a closer look.

In the "Additional Board Manager URL" box, make sure you have the following two json files included. If you do not have them, add them to your preferences.


If you have more than one json file, you can click on the button outlined in red and add the json links at the end. It'll look something like the following:

Additional Boards Manager URL location in the Preferences Dialog

Having a hard time seeing? Click the image for a closer look.

Once you've got your preferences updated, go to Tools -> Board and select the Boards Manager like so:

Arduino Boards Manager Dialog, under Tools

Having a hard time seeing? Click the image for a closer look.

Search for "ESP32", and you should find both the esp32 and SparkFun ESP32 Boards board packages. Make sure the latest version selected and click Install for the esp32 boards. Repeat for the SparkFun ESP32 Boards.

Board manager showing SparkFun ESP32 Boards install

Having a hard time seeing? Click the image for a closer look.

Once the board definitions have been installed, you should see the SparkFun ESP32 Thing Board under your Tools -> Board -> SparkFun ESP32 Arduino menu. The smôl ESP32 uses the same board definition as the SparkFun ESP32 Thing; select that (and ignore the Thing Plus, MicroMod and LoRa Gateway options).

DropDown showing tools->Board->SparkFun ESP32 Arduino->SparkFun ESP32 MicroMod

Note: Our board definition package should install all of the tools needed to compile code for the ESP32. If you run into trouble having code compile or downloading due to tools not being found, you may need to install Espressif's Arduino ESP32 package manually.

Voila! You're ready to rock with your smôl ESP32 Processor Board!

Arduino Example: RGB_LED

With the SparkFun ESP32 Arduino core installed, you're ready to begin programming. Make sure you have the ESP32 Thing definition selected under your Tools > Board menu, then it is time to connect your smôl ESP32 to your computer using a USB-C cable.

Next, select your serial port under the Tools > Port menu.

Port Selection for the ESP32 MicroMod Processor Board
Having a hard time seeing? Click the image for a closer look.

You can also select the Upload Speed: "921600" baud -- the fastest selectable rate -- will get the code loaded onto your ESP32 the fastest, but may fail to upload once-in-a-while. (It's still way worth it for the speed increase!)

Loading the RGB_LED Demo

To make sure your toolchain and board are properly set up, we'll upload a simple sketch -- RGB_LED! The WS2812C LED on the ESP32 Processor Board is perfect for this test. Copy and paste the example sketch below into a fresh Arduino sketch:

// smôl ESP32 LED Demo
// Select SparkFun ESP32 Thing as the board
// Make sure you have the correct drivers installed for the Silicon Labs
// CP210x USB to UART Bridge otherwise the automatic upload may fail

#include <FastLED.h> // http://librarymanager/All#FastLED

#define LED_PIN     25 //GPIO25 on smôl ESP32 is connected to WS2812 LED
#define CHIPSET     WS2812
#define NUM_LEDS    1

#define BRIGHTNESS  50


uint8_t gHue = 0; // rotating "base color" used by many of the patterns

void setup() {
    delay(30); // sanity delay
    FastLED.addLeds<CHIPSET, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );
    FastLED.setBrightness( BRIGHTNESS );

void loop()
  fill_rainbow( leds, NUM_LEDS, gHue, 7);;

  EVERY_N_MILLISECONDS( 10 ) { gHue++; } // cycle the "base color" through the rainbow

With everything set up correctly, click the arrow icon to upload the code! Once the code finishes transferring, the RGB LED should start cycling through all the colors of the rainbow. Hypnotic isn't it?!


If you haven't used the fantastic FastLED library before, you will need to install it through the IDE Library Manager. The easiest way to do that is to click the link next to the #include <FastLED.h>. When the Library Manager has finished searching, select the latest version of FastLED and click Install.

If the code fails to upload when you click the upload (arrow) icon, check you have the correct port selected and have the official CP210x driver installed. If you're trying to use a generic USB driver, it won't be able to initialize the Bootloader via DTR and RTS pins.

Further Examples

You can find more tried-and-tested examples in the GitHub repo:

  • SPIFFS_Test will format part of the Processor Board's flash memory as an SPI Flash File System and check it is working correctly by creating, editing, renaming and deleting a text file
  • SimpleWiFiServer is a fun little demo:
    • Edit the code and replace yourssid and yourpasswd with the name and password of your WiFi network
    • Upload the code and open the Arduino IDE Tools > Serial Monitor at 115200 baud to see the diagnostic messages
    • Make a note of the smôl ESP32's IP Address
    • Open a web browser on your computer and open the web page at http://nnn.nnn.nnn.nnn where nnn.nnn.nnn.nnn is the smôl ESP32's IP address
    • Click the web page buttons to change the color of the RGB LED


Not working as expected and need help? SparkX products are rapidly produced to bring you the most cutting edge technology as it becomes available. These products are tested but come with no guarantees. Live technical support is not available for SparkX products. Head on over to our forum for support or to ask a question and we will get back to you as soon as we can.

Resources and Going Further

For more information about the smôl ESP32 Processor Board, check out the following links:

smôl Documentation:

ESP32 Documentation: