ESP32 Pinout notes for making a breakout module on a dual row IDC header

ESP32-Pinout-Notes.txt

ESP32 Pinout notes:

What is superflous or can be on the carrier PCB and doesn't require pass-through to the header?
---------------------------------------------------------------------------------------------
After some thinking and logically grouping things...
Desired order of 26 pin header:
pin 1 -Y GND - Ground
pin 6 ?Y GPIO-34 - ADC6/RTC_GPIO4 (RTC_WAKEUP)
pin 7 ?Y GPIO-35 - ADC7/RTC_GPIO5 (RTC_WAKEUP) (FTDI CTS unless there's a better pin?)
pin25 -Y GPIO-00 - ADC11/Touch1/BOOT/EMAC_TX_CLK/RMII_CLK_OUT (default pullup)
pin 2 -Y 3v3 - Main Power input
pin26 -- GPIO-04 - ADC10/Touch0 (default pulldown)
pin34 -Y GPIO-03 - UART0_RXD0
pin12 ?Y GPIO-27 - ADC17/Touch7/RTC_GPIO17/RMII_CRS_DV
pin35 -Y GPIO-01 - UART0_TXD0
pin33 -Y GPIO-21 - I2C SCL / RMII_TX_EN
pin 3 ?? Enable/Reset - Pulled low with a 12k resistor (default pullup) (DTR/RTS reset circuit)
pin36 -Y GPIO-22 - I2C SDA / RMII_TXD[1]

Stop here for a basic 12 pin module with wakeup, i2c, and ftdi-style 6-pin inline serial.
FTDI style is: GND, CTS, VCC, TXD, RXD, RTS

pin37 -Y GPIO-23 - VSPI MOSI
pin31 -Y GPIO-19 - VSPI MISO / RMII_TXD[0]
pin30 -Y GPIO-18 - VSPI SCK (SPI Clock)
pin29 -Y GPIO-05 - VSPI SS (default pullup)
Stop here for a basic 16 pin module with SPI.

pin10 ?Y GPIO-25 - ADC18/DAC1_AUDIO/RTC_GPIO6/RMII_RXD[0]
pin11 ?Y GPIO-26 - ADC19/DAC2_AUDIO/RTC_GPIO7/RMII_RXD[1]
Stop here for a 18 pin module with two additional 8bit DAC outputs.

pin28 -Y GPIO-17 - UART2_TXD / RMII_INT_OSC_CLK_OUT_180
pin27 -Y GPIO-16 - UART2_RXD / RMII_INT_OSC_CLK_OUT
Stop here for a 20 pin module with a second serial port or full RMII ethernet.

pin17 -Y GPIO-09 - FLASH/SDIO D2
pin18 -Y GPIO-10 - FLASH/SDIO D3
pin19 -Y GPIO-11 - FLASH/SDIO CMD
pin20 -Y GPIO-06 - FLASH/SDIO SCK (SPI Clock)
pin21 -Y GPIO-07 - FLASH/SDIO D0
pin22 -Y GPIO-08 - FLASH/SDIO D1
Stop here for a 26 pin module with SDIO.

14+6 pins = 26 pins, These six are shared with the on-module SPI flash chip.
Since they're optional, these will be 21-26, the six pins at the end of 26pin header.
These last 6 will be skippable to get a 20 pin module pinout.

Here it is again, in module pin order:
---------------------------------------------------------------------------------------------
Total Retained: 26 pins + JTAG header (HSPI)
JTAG/HSPI Header + ground + 3.3v = 6 pin header:
pin13 -N GPIO-14 - HSPI_SCK/ADC16/Touch6/JTAG_TMS (SPI clock) 
pin14 -N GPIO-12 - HSPI_MISO/ADC15/Touch5/JTAG_TDI (default pulldown)
pin16 -N GPIO-13 - HSPI_MOSI/ADC14/Touch4/JTAG_TCK (JTAG clock)
pin23 -N GPIO-15 - HSPI_SS/ADC13/Touch3/JTAG_TDO (default pullup)
pulldown on GPIO-15 to disable bootlog on UART_TXD0 (do not populate)
pullup on GPIO-12 for 1.8V SDIO/IO (do not populate)

software pullup after boot with dim Red SMT LED at:
pin24 -N GPIO-02 - ADC12/Touch2 (default pulldown)

Main header requires (In module pin order):
pin 1 -Y GND - Ground
pin 2 -Y 3v3 - Main Power input
pin 3 ?? Enable/Reset - Pulled low with a 12k resistor (default pullup)
pin 6 ?Y GPIO-34 - ADC6/RTC_GPIO4 (RTC_WAKEUP)
pin 7 ?Y GPIO-35 - ADC7/RTC_GPIO5 (RTC_WAKEUP)
pin10 ?Y GPIO-25 - ADC18/DAC1_AUDIO/RTC_GPIO6/RMII_RXD[0]
pin11 ?Y GPIO-26 - ADC19/DAC2_AUDIO/RTC_GPIO7/RMII_RXD[1]
pin12 ?Y GPIO-27 - ADC17/Touch7/RTC_GPIO17/RMII_CRS_DV
8 pins, nothing more to gain here with the RTC_XTAL & ADC_PREAMP cap in place.

pin17 -Y GPIO-09 - FLASH/SDIO D2
pin18 -Y GPIO-10 - FLASH/SDIO D3
pin19 -Y GPIO-11 - FLASH/SDIO CMD
pin20 -Y GPIO-06 - FLASH/SDIO SCK (SPI Clock)
pin21 -Y GPIO-07 - FLASH/SDIO D0
pin22 -Y GPIO-08 - FLASH/SDIO D1
8+6 pins = 14 pins, These six are shared with the on-module SPI flash chip.
Since they're optional, these will be 21-26, the six pins at the end of 26pin header.
These last 6 will be skippable to get a 20 pin module pinout.

pin25 -Y GPIO-00 - ADC11/Touch1/BOOT/EMAC_TX_CLK/RMII_CLK_OUT (default pullup)
pin26 -- GPIO-04 - ADC10/Touch0 (default pulldown)
pin27 -Y GPIO-16 - UART2_RXD / RMII_INT_OSC_CLK_OUT
pin28 -Y GPIO-17 - UART2_TXD / RMII_INT_OSC_CLK_OUT_180

pin29 -Y GPIO-05 - VSPI SS (default pullup)
pin30 -Y GPIO-18 - VSPI SCK (SPI Clock)
pin31 -Y GPIO-19 - VSPI MISO / RMII_TXD[0]

pin33 -Y GPIO-21 - I2C SCL / RMII_TX_EN
pin34 -Y GPIO-03 - UART0_RXD0
pin35 -Y GPIO-01 - UART0_TXD0
pin36 -Y GPIO-22 - I2C SDA / RMII_TXD[1]

pin37 -Y GPIO-23 - VSPI MOSI
14 + 4 + 4 + 4 = 26 pins total.
---------------------------------------------------------------------------------------------
FULL PIN LIST:
PINID,SUPERFLOUS,HOST_USES,COMMON_NAME,ALT_MODES,DESCRIPTION

pin 1 -Y GND - Ground
pin 2 -Y 3v3 - Main Power input
pin 3 ?? Enable/Reset - Pulled low with a 12k resistor (default pullup)
pin 4 XN GPIO-36 - SVP/RTC_GPIO0 - Positive side of Capacitor for ADC preamp
pin 5 XN GPIO-39 - SVN/RTC_GPIO3 - Negative side of Capacitor for ADC preamp
pin 6 ?Y GPIO-34 - ADC6/RTC_GPIO4 (RTC_WAKEUP)
pin 7 ?Y GPIO-35 - ADC7/RTC_GPIO5 (RTC_WAKEUP)
pin 8 XN GPIO-32 - ADC4/Touch9/RTC_GPIO9 - Positive side of RTC's 32khz crystal
pin 9 XN GPIO-33 - ADC5/Touch8/RTC_GPIO8 - Negative side of RTC's 32khz crystal
pin10 ?Y GPIO-25 - ADC18/DAC1_AUDIO/RTC_GPIO6/RMII_RXD[0]
pin11 ?Y GPIO-26 - ADC19/DAC2_AUDIO/RTC_GPIO7/RMII_RXD[1]
pin12 ?Y GPIO-27 - ADC17/Touch7/RTC_GPIO17/RMII_CRS_DV
pin13 -N GPIO-14 - HSPI_SCK/ADC16/Touch6/JTAG_TMS (SPI clock) 
pin14 -N GPIO-12 - HSPI_MISO/ADC15/Touch5/JTAG_TDI (default pulldown)
pin15 XN GND - Ground
pin16 -N GPIO-13 - HSPI_MOSI/ADC14/Touch4/JTAG_TCK (JTAG clock)
pin17 -Y GPIO-09 - FLASH/SDIO D2
pin18 -Y GPIO-10 - FLASH/SDIO D3
pin19 -Y GPIO-11 - FLASH/SDIO CMD (huh?)
pin20 -Y GPIO-06 - FLASH/SDIO SCK (SPI Clock)
pin21 -Y GPIO-07 - FLASH/SDIO D0
pin22 -Y GPIO-08 - FLASH/SDIO D1
pin23 -N GPIO-15 - HSPI_SS/ADC13/Touch3/JTAG_TDO (default pullup)
pin24 -N GPIO-02 - ADC12/Touch2 (default pulldown)
pin25 -Y GPIO-00 - ADC11/Touch1/BOOT/EMAC_TX_CLK/RMII_CLK_OUT (default pullup)
pin26 -- GPIO-04 - ADC10/Touch0 (default pulldown)
pin27 -Y GPIO-16 - UART2_RXD / RMII_INT_OSC_CLK_OUT
pin28 -Y GPIO-17 - UART2_TXD / RMII_INT_OSC_CLK_OUT_180
pin29 -Y GPIO-05 - VSPI SS (default pullup)
pin30 -Y GPIO-18 - VSPI SCK (SPI Clock)
pin31 -Y GPIO-19 - VSPI MISO
pin32 XN NC - devboard shows GND label?
pin33 -Y GPIO-21 - I2C SCL / RMII_TX_EN
pin34 -Y GPIO-03 - UART0_RXD0
pin35 -Y GPIO-01 - UART0_TXD0
pin36 -Y GPIO-22 - I2C SDA / RMII_TXD[1]
pin37 -Y GPIO-23 - VSPI MOSI
pin38 XN GND - Ground

I am a bit puzzled about the functionality of pin below:

software pullup after boot with dim Red SMT LED at:
pin24 -N GPIO-02 - ADC12/Touch2 (default pulldown)

In the case of the ESP32 Uno R3 board, which mimics the pin layout of Arduino Uno R3, I am forced to use a shield having this pin used as ADC0 in Arduino world.
So GPIO02 will be redefined as an ADC... a pot will be connected to this pin, to provide a variable voltage.
The question is... what happens with LED behaviour ? Will the LED pullup circuitry influence the ADC operation ?

I am a bit puzzled about the functionality of pin below:

software pullup after boot with dim Red SMT LED at:
pin24 -N GPIO-02 - ADC12/Touch2 (default pulldown)

In the case of the ESP32 Uno R3 board, which mimics the pin layout of Arduino Uno R3, I am forced to use a shield having this pin used as ADC0 in Arduino world. So GPIO02 will be redefined as an ADC... a pot will be connected to this pin, to provide a variable voltage. The question is... what happens with LED behaviour ? Will the LED pullup circuitry influence the ADC operation ?

Almost all of the currently supported ESP32 board layouts in arduino define LED_BUILTIN to gpio2.
So if you don't select the correct board in the IDE, you most certainly could disturb the ADC operation.

I've never produced this IDC-20 connector board with the red LED on pin 24/GPIO2 (not routed to the pin connector rows), but I chose it because it was the common default pin to use for LED_BUILTIN, and I did not want the LED to be a "power" LED, active by default.

I HATE devices that have constant power indicators.

However, LED_BUILTIN can also be dimmed, either by using PWM/AnalogOut, or changing the LED resistor to a higher value, which also reduces current draw.

Were you to run code intended for my board on your random uno-layout board, the pullup would be switched on and you would be getting a constant high on the pin. So yes, absolutely, in GPIO output mode, it is useless for ADC input.

But of course, if you run blink.ino without changes, and without setting the correct ESP Uno R3 board type; you'd have the same issue.

Thanks for stopping by, though! (Even though this is for a hardware specification that was never produced.)

In the case of the ESP32 Uno R3 board, which mimics the pin layout of Arduino Uno R3, I am forced to use a shield having this pin used as ADC0 in Arduino world. So GPIO02 will be redefined as an ADC... a pot will be connected to this pin, to provide a variable voltage. The question is... what happens with LED behaviour ? Will the LED pullup circuitry influence the ADC operation ?

Oh, and so you don't walk away empty handed -- all you need to do for your pot is select the correct pullup/pulldown state in your sketch.
GPIO2 defaults to pulldown (grounded) at powerup (off), safe to use as an AnalogIn(). If you set the GPIO to pullup, it will immediately raise to the VCC level (3.3V) with a ~6-20mA current delivery ability. Enough to drive a transistor or a resistor current limited LED, and useful for AnalogOut() (PWM/DAC?) but not AnalogIn() (esp32s-audio-quality-non-linear-ADC).

Also, beware, some pins default to pullup at boot, such as GPIO-15, or GPIO-0/BOOT/Button, with ground on the other side of the button. This will sink a small current from the chip. If the button's far side was directly connected to VCC without a resistor, and the pulldown mode was active, more current than possibly safe may flow inward through the GPIO pin instead of the VCC pin, and this can cause problems, or just cause the chip to remain alive from an alternative VCC source coming in from a GPIO sink. Without the radio on, the ESP32 only consumes about 30mA, and may continue running from parasitic voltage in such a configuration. Hope that helps!