ESP32-S2 Dev Board

Design Details

Design Specifications(Default):

4MB External SPI Flash
SPI Boot
Serial Programming(no external programmer needed, just a usb micro A connector)
UART and power delivery over the same programming connector.
USB2.0 connection(usb type B micro)
22 GPIO's and one DAC are broken out.
A single User Controllable LED.
No RF capabilities(If you want this just ask and Ill add the antenna design I have for this.)

Why I made this...

The purpose of this design was to initially to get familiar with this lower power variant of the ESP32 platform and the specific design needs that relate to it.There are not many things to worry about in terms of the layout, especially true for my implementation. Obviously one should use the best routing practices possible...but not much time was spent on that. This entire design and layout was completed in about 2 hours. With that in mind routing and part placement could 100% be better, but has had no impact on performance of this design. there was zero intention of doing anything with this design but it seems that similar hobbyist level products were a little pricey for what they offered, had 0 support/documentation, and were not customizable for their needs/price points.

Therefore, this design is being made available as:

A package that would allow others to directly create their own copy of this and makes tweaks along the way.
A purchasable item that they could buy pre-assembled or assemble themselves.(coming soon)
An information resource to get familiar with the Espressif platform, while avoiding some of the struggles that getting familiar with this product line generally introduces.

Clarifying the Absent

Flash Memory

Not any SPI flash memory can be used for storing your boot code. They are limited to the following vendors:

GigaDevice

Winbond

This design initially attempted to use a microchip SPI flash chip, but the commands used to to access user code following the startup of the FSBL(First Stage Boot-loader) do not work out of the box.

There may be a way to modify what those are, but it is not immediately obvious. However! you should be able to use just about any SPI flash you want if you don't plan to boot from it. You MUST provide a SPI flash of to in order to program this device. The ESP32-S2 only comes with internal ROM which cannot be programmed in the same way.

Auto Program

Reference Figure 1, notice two transistor circuits(Q2 and Q3) attached to the USB to serial converter(U1).

This is used to place the ESP32-S2 into download mode(whatever you want to call it). What this does is pulls GPIO_0 (boot strapping pin)low and then toggles the reset.

You can manually do the same thing by holding (not shown in any Figure on this page)BOOT1 and then toggling RST_PROG while continuing to hold BOOT1 low.

Figure 1: Serial communication and Serial Flash Programming

Power-up and Reset Timing

One thing that may be easy to miss is the Power-up/Reset timing requirements. Be sure that you don't just "tie" the Reset pin(Named CHIP_PU in the Datasheet) to VDD.

For power on it suffices to just throw a RC timer on the pin that meets this 50uS requirement. In the included Design a 10k resistor and a 0.1u ceramic capacitor.

For Discharge you refer to Figure 3. As you can see the PNP BJT(Q1) is disabled when input power is supplied. When active it discharges the power circuitry in roughly 60mS.

NOTE: C13 says "TBD" but a 1u ceramic capacitor was used during assembly. Additionally if you expect your power to at times exceed the device rated 3.6V, you should place a TVS diode(transient voltage suppressor) on your input power or implement a different protection scheme

Figure 2: Power-up and Reset Timing Requirements

Figure 3: Input Power and Discharge Circuitry

Register Access

So accessing registers can be sort of "odd" for this device. Normally you can define and bit-shift in the values you want to use for various register level operations(GPIO toggling, UART buffers, etc.)

However, you have to use "REG_Write(register, value)", and "Reg_Read(register)" in order to do this.

Even less conveniently it appears that the "defined register names" in the TRM(Technical Reference Manual) do not match what is in the header files for the various ES32-Sx models. The workaround that I have used that has yet to "break" is either using the hex value register address directly or assigning that hex address my own memorable name. This is not ideal, but gets the job done. You will also find that the TRM does not define these commands, and I only located them by perusing forums. So don't be surprised if you end up using "less than documented" code.

Links to Design Materials/Referenced Documents

ESP32-S2 Technical Reference Manual

ESP32-S2 Datasheet

ESP32-Dev Github

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