#363 Which ESP32 pins are safe to use?

Summary

This video offers an in-depth look at the ESP32 microcontroller, focusing on its pins and their specific functions. It provides a detailed overview of the 40 GPIO pins, highlighting which ones to use or avoid for various projects. The video also covers the importance of consulting the datasheet, handling strapping pins, and using pins for specific interfaces like I2C, SPI, and PWM. Additionally, it discusses advanced features like ADC inputs, DAC outputs, interrupts, and touch sensors. The host shares practical tips for pin selection to optimize project design and performance.

Takeaways

• 😀 The ESP32 has 40 GPIO (General Purpose Input Output) pins, but not all are truly general purpose.
• 🔍 GPIO pins 34 through 39 are actually GPI (General Purpose Input) pins and should not be used as output pins.
• ⚠️ GPIO 34 and 35 are particularly dangerous if used for output without proper precautions.
• 🔌 GPIO 6 to 11 are connected to an external flash memory chip and should be avoided unless you know what you are doing.
• 🔄 GPIO 36 and 39 are typically labeled as sensor VP and sensor VN and have special functions.
• 🚫 Strapping pins like GPIO0 and GPIO2 have functions during boot up and should be handled carefully to prevent boot issues.
• 🔌 RX/TX pins (GPIO1 and 3) are commonly used for flashing and debugging and should not be altered.
• 🔄 The ESP32 has two I2C interfaces, typically using GPIO21 and 22, which can be reconfigured to other pins if needed.
• 🔄 Two SPI interfaces are available, with the third SPI bus used for the flash memory chip.
• 🔌 GPIO 12 to 15 should be reserved for debugging purposes if using the inline debugger of PlatformIO.
• 🔋 GPIO 34 through 39 can be used as ADC (Analog to Digital Converter) input pins, though the quality of the ADC results may not be excellent.
• 🎵 The ESP32 has two 8-bit DAC (Digital to Analog Converter) outputs on GPIO 25 and 26, which are simple to program.

Q & A

What is the primary focus of the video script about the ESP32?

The primary focus of the video script is to explore the ESP32's pins, create a priority pin list, and provide insights on how to effectively use the ESP32's various pins for projects.

How many GPIO pins does the ESP32 have according to the datasheet?

According to the datasheet, the ESP32 has 40 GPIO pins numbered from GPIO0 to GPIO39.

Why are GPIO 34 through 39 not considered general purpose input output pins?

GPIO 34 through 39 should be called GPI pins because they cannot be used as output pins, and using them for output without caution can lead to confusion and wasted troubleshooting time.

What special function do GPIO 36 and 39 have in the ESP32?

GPIO 36 and 39 are usually labeled as sensor VP and sensor VN, indicating they have a special function, but the exact purpose is not detailed in the script.

Why are GPIO 6 to 11 not recommended for general use in ESP32 modules like the Vroom or the Vrover?

GPIO 6 to 11 are connected to an external flash memory chip used for data storage, making them 'forbidden' for general use unless the user knows exactly what they are doing.

What is the purpose of the strapping pins in the ESP32 during boot up?

Strapping pins have a function during boot up, and if wrongly connected, they can prevent the ESP32 from booting properly.

Why should GPIO0 and GPIO2 not be used for projects without a specific need?

GPIO0 and GPIO2 have hidden functions that are important during the boot process and firmware flashing. Using them without a specific need can lead to complications and difficulty in troubleshooting.

What are the standard pins used for the ESP32's I²C interface?

The standard pins used for the ESP32's I²C interface are GPIO21 and GPIO22, but they can be changed to most other GPIO pins using specific commands.

How many SPI interfaces does the ESP32 have, and which pins are used for them?

The ESP32 has two usable SPI interfaces that use different sets of pins. The standard libraries use the VSPI pins as shown in the SPI example sketch.

What is the purpose of the ADC pins on the ESP32, and are there any limitations when using them with Wi-Fi?

The ADC pins on the ESP32 are used for analog-to-digital conversion. However, all pins starting with ADC2 cannot be used if Wi-Fi is enabled, limiting the available ADC pins for use.

How can the ESP32's GPIO pins be used for PWM, and what is unique about its implementation compared to Arduino?

The ESP32 can use all GPIOs for PWM to control devices like servos or dim LEDs. Unlike Arduino, which uses 'analogWrite', the ESP32 requires defining the frequency and resolution of a channel before attaching it to a pin and writing to the channel.

What is the purpose of interrupts in the ESP32, and how flexible are they in terms of pin usage?

Interrupts allow an external signal to interrupt any running sketch, simplifying some projects. The ESP32 is flexible with interrupts, allowing the use of all pins for this purpose, although it is not very fast in handling interrupts.

What are the exotic usages of pins discussed in the script, and how many pins can be used for touch sensors?

The script discusses touch sensors and hall sensors as exotic usages of pins. Out of the 10 pins that can be used for touch sensors, 8 can be considered after excluding special pins.

Outlines

00:00

😎 Exploring ESP32's Pin Secrets and Prioritization

This paragraph introduces the ESP32 microcontroller, highlighting its extensive pin capabilities. The video aims to provide an overview of all ESP32 pins, focusing on their specific purposes and the importance of careful handling. The speaker emphasizes the need to consult the datasheet for accurate pin information and shares a strategy for utilizing the numerous pins in projects. The discussion includes the limitations of certain pins, such as GPIO 34-39, which are not suitable for output functions. Additionally, the paragraph touches on the use of strapping pins during boot-up and their potential to prevent the device from booting if connected incorrectly. The speaker also mentions the external flash memory chip connected to GPIO 6-11 and the need to avoid using these pins unless absolutely necessary.

05:01

🤖 Prioritizing ESP32 Pins for Project Use

This paragraph delves deeper into the prioritization of ESP32 pins for various project requirements. The speaker discusses the standard SPI and I2C interfaces, emphasizing the importance of reserving certain pins for these functions to avoid conflicts. The paragraph also addresses the need to reserve GPIO 12-15 for debugging purposes when using the inline debugger of PlatformIO. The speaker then explores the secondary functions of pins, such as ADC inputs, and suggests using GPIO 34-39 for these purposes while noting the limitations when using Wi-Fi. The paragraph further covers the use of GPIO 25 and 26 for 8-bit DAC outputs and the flexibility of using all GPIOs for PWM functions. The speaker also highlights the versatility of the ESP32 in handling interrupts and the use of RTC GPIO pins for waking the device from deep sleep. Finally, the paragraph touches on the exotic uses of pins, such as touch sensors and a hall sensor, and provides guidance on how to choose pins based on project needs.

10:02

🔍 Choosing Pins for ESP32 Projects

In this final paragraph, the speaker provides a summary of how to choose pins for ESP32 projects. The focus is on starting with a priority one list of pins and considering the use of GPIO 34-39 for analog input or wake-up functions if more pins are needed. The speaker advises sticking to standard I2C or SPI pins due to library constraints, especially from Arduino, which may not allow pin changes. The paragraph also mentions the flexibility of changing pins in PCB designs to ease the layout process. The speaker encourages viewers to share their insights and experiences in the comments and reminds them of the importance of supporting the channel for its continued existence.

Keywords

💡ESP32

ESP32 is a microcontroller with Wi-Fi and Bluetooth capabilities, known for its versatility and power. In the video, it's referred to as a 'beast' with 'secrets,' highlighting its complex features and capabilities. The script discusses the various pins and functionalities of the ESP32, emphasizing its extensive GPIO (General Purpose Input Output) pins.

💡GPIO Pins

GPIO stands for General Purpose Input Output, which are pins on a microcontroller used for various input and output functions. The video script discusses the ESP32's 40 GPIO pins, numbered from GPIO0 to GPIO39, and how not all of them are truly general purpose, with some having specific functions or restrictions.

💡Datasheet

A datasheet is a document that provides detailed information about a component, such as pin functions, electrical characteristics, and operating conditions. The script mentions consulting the ESP32 datasheet as the primary source of wisdom for understanding the chip's capabilities and pin functions.

💡Strapping Pins

Strapping pins are used during the boot-up process of a microcontroller and can affect its operation if not connected correctly. In the script, GPIO0 and GPIO2 are identified as strapping pins with specific boot functions, and the video advises caution when using them to avoid boot issues.

💡ADC Pins

ADC stands for Analog to Digital Converter, which is used to convert analog signals into digital values that a microcontroller can process. The video script explains that the ESP32 has several ADC pins, but not all can be used simultaneously with Wi-Fi, which is a common function of the ESP32.

💡DAC Outputs

DAC stands for Digital to Analog Converter, which converts digital signals into analog form. The script mentions that the ESP32 has two 8-bit DAC outputs on GPIO 25 and 26, which can be used to generate analog signals, such as for creating sine waves.

💡PWM

PWM stands for Pulse Width Modulation, a technique used to encode a message into a pulse signal whose duty cycle varies. In the context of the video, PWM is used to control devices like servos or dim LEDs by generating a square wave signal with a variable on/off ratio.

💡Interrupts

Interrupts are a feature of microcontrollers that allow external signals to temporarily halt the normal execution of the program. The video script discusses how all pins of the ESP32 can be used for interrupts, which can simplify programming by allowing for immediate responses to external events.

💡RTC GPIO Pins

RTC stands for Real-Time Clock, and RTC GPIO pins are used for waking up the microcontroller from deep sleep. The script mentions that GPIO34 through 39 can be used as RTC GPIO pins, which is a way to save the more versatile priority one pins for other uses.

💡Touch Sensors

The ESP32 has the capability to use certain pins as touch sensors, allowing for touch input without the need for external components. The script notes that 10 pins can be used for touch sensors, but after excluding special pins, 8 remain for this purpose.

💡Hole Sensor

The hole sensor is a less common feature of the ESP32, which can detect the presence of a magnet or metal. The video script describes it as an 'exotic' function, suggesting it may not be commonly used but is an interesting capability of the microcontroller.

Highlights

Overview of ESP32 pins and creation of a priority pin list for efficiency.

Introduction to the unique functions of specific ESP32 pins.

Explanation of general-purpose input-output (GPIO) pins and their numbering.

Discussion on non-existent GPIO pins and their impact on usage.

Distinction between true GPIO pins and those with restricted functions.

Identification of pins connected to external flash memory and their restrictions.

Introduction to strapping pins and their role during boot-up.

Highlighting the hidden functions of GPIO0, GPIO2, GPIO5, and GPIO15.

Insight on development board pins used for flashing and debugging.

Explanation of I2C interfaces and their standard pins.

Overview of SPI interfaces and their standard pins.

Details on pins used for debugging sketches in PlatformIO.

Discussion on secondary functions of pins, such as ADC inputs and DAC outputs.

Introduction to PWM and its usage across all GPIO pins.

Explanation of interrupts and their application on ESP32 pins.

Introduction to RTC GPIO pins for waking the ESP32 from deep sleep.

Overview of exotic functions like touch sensors and the hall sensor.

Recommendations on choosing pins for various project requirements.

Emphasis on using standard I2C and SPI pins for compatibility with libraries.

Encouragement to experiment with interrupts to simplify sketches.

Transcripts

the esp32 is a beast with some secrets

today we will look at its pins and

create a priority pin list which saves

you a lot of time and hassle

crazy youtubers here is the guy with the

swiss accent with a new episode and

fresh ideas around sensors and

microcontrollers

remember if you subscribe you will

always sit in the first row

in this video we will get an overview of

all pins of the esp32

learn which pins have particular

purposes and therefore have to be

treated with care

learn the real universally usable prints

create a strategy on how to use the many

pins for our projects

and do some programming examples

the most important source of wisdom for

parts always is the datasheet if we

consult the esp32 datasheet it looks

like the chip has 40 gpio pins

numbered from

gpio0 to gpio39

gpio by the way

means general purpose input output pins

i copied this overview sheet into excel

like that we can filter and sort it as

we wish

of course you find a link to it in the

description

if we have a close look we see that only

32 pins are labeled gpio

gpio 20 24 28 through 31

37 and 38 do not exist

please don't ask me why

but still 32 is a lot compared with the

esp8266

or the arduino uno

the next surprise

not all those pins are general purpose

as the name implies

gpio 34 through 39 should be called gpi

pins

they cannot be used as output pins

mostly 34 and 35 are dangerous if you do

not pay attention and try to use them

for output

no warning will pop up and after hours

you think you are stupid

gpio 36 and 39 usually are labeled as

sensor vp and sensor vn

we will later see that they have a

special function

so there are 28 true gpio pins left

esp32 modules like the vroom or the

vrover use an external flash memory chip

to store data so gpio 6 to 11 are

connected to this flash chip and are

forbidden for us unless you exactly know

what you do

still 22 potentially true gpio pins are

left

next are the so called strapping pins

they have a function during boot up and

if wrongly connected prevent your esp32

from booting

gpio0 is well known to us

sometimes we have to press a boot button

which tells the chip that we want to

flash a new firmware

definitely not a general purpose pin

we should not use it unless we

absolutely need it

and then make sure it is always high

during boot

gpio2 also has a hidden function if you

pull it high during boot you are not

able to flash new content

also here you will search for the error

for a long time

gpio5

also seems to have a function but i did

not see a disadvantage by pulling it low

or high

other than the mtdo or gpio15

if you pull this pin low

the esp32 does not show the lock anymore

at bootup

if you do not know it you probably will

search for a problem which in reality is

none

gpio0 and gpio2 should not be used for

projects without need

20 pins are left

most development boards use rxtx for

flashing and debugging

these are gpio1 and 3.

we should not touch them too

18 pins left

often we need an i-square-c interface

the esp32 has two such interfaces

because we can attach up to 112 sensors

to one connection

we usually only need one

the standard pins are

gpio2122

and can be changed with this command to

most other gpio pins

for this place for example the fast spi

interface is the right choice

the esp32 has two usable spi interfaces

that use the following pins

the third spi bus is used for the flash

memory chip by the way

standard libraries use the vspi pins as

shown in the spi example sketch

because many sensors offer an isquare-c

interface i usually do not use these two

pins for other purposes

16 pins left

if you plan to debug your sketch using

the inline debugger of platform io you

have to spare gpio 12 to 15 out for your

project

12 pins left this is my priority one

pins list

i always start to use these pins

only on pcb layouts it might be handy to

use other pins

or if you really need a lot of pins

then you can use the flexibility of the

esp32 to change pins for functions like

i square c serial or spi

next we have a look at the secondary

function of pins for example the

datasheet shows us many adc pins

unfortunately all pins starting with adc

2 cannot be used if we use wifi

and who is not using wi-fi with the

esp32

a good thing

gpio 34 through 39 can be used as adc

input pins

my preferred solution to relieve my

priority 1 pin list

just keep in mind the esp32 adc results

are not excellent as shown in video

number 340

but good enough to measure battery

voltage for example you can easily add

two resistors and monitor a 4.2 volts

lighon battery

the esp-32 also has two 8-bit dac

outputs

on gpio 25 and 26

they are very simple to program

just use this command

and the results are ok as we see here

we can also create sine waves for

example with this function

next comes pwm

in this mode pins generate a square wave

signal with a variable on off ratio

such signals are used to control servos

for example or dim leds

fortunately we can use all gpios for pwm

just a curiosity

the esp32 never got the same

implementation as the arduino where

analog write

is used

also not the best choice if you ask me

but the esp32 implementation is even

more adventurous

it seems that somebody wrote a function

to dim leds and then it stayed like that

first we have to define the frequency

and the resolution of a channel

then we have to attach this channel to a

pin

after that we can start to write to this

channel

as we see here the esp32 can create

relatively high frequencies which might

be interesting for some projects

anyway these were the typical usages of

gpio pins in projects with one exception

interrupts

interrupts are a great functionality of

most mcus

we can interrupt any running sketch with

an external signal which can drastically

simplify some sketches

as we saw in video number 328 the esp32

is not very fast in this discipline but

we can use all pins for that purpose

very flexible

if you never used it i strongly suggest

trying interrupts at least once

if we want to use an interrupt pin to

wake the esp32 from deep sleep we have

to use so called rtc gpio pins

here we see like with the adcs that we

can use

gpio34 through 39 to save our priority

one pins

now we definitely come to the exotic

usages of pins

the first being touch sensors

10 pins can be used for that purpose

if we exclude the special pins we still

get 8 pins

so far i had no projects with them i

only played around

maybe you know of cool projects using

these pins

and the last even more exotic function

is a hole sensor

here i have no idea why it is built in

definitely a solution on the search for

a problem because even strong magnets do

not influence the whole sensor over

distance

so i prefer to use such a small hole

sensor chip that can be mounted where

the action is and keep the esp32 away in

a safe case

just in case you want to use this hole

sensor it is connected to gpio36

and 39

you must leave these pins open if you

want to use the sensor

that's it

the last remaining question is

how do i choose the pins

i start with my priority one list

if i expect that they will not be

sufficient i use the gpi pins for analog

input or wake up

i try to stick with the standard i

square c or spi pins as some libraries

do not allow to change pins

especially libraries coming from the

arduino only use wire begin which use

standard pins

only in rare cases i switch standard

pins

for example if i need three serial

connections standard serial one pins are

mapped to pins used by the flash chips

if i design pcbs i sometimes use the

flexibility of changing pins to ease the

design

those are my two synths i'm sure you

have a lot to add in the comments

as always you find all the relevant

links in the description

i hope this video was useful or at least

interesting for you if true please

consider supporting the channel to

secure its future existence thank you

bye