Design the programming USB to UART circuit

[austindriggs]

SUMMARY

The ESP32 needs to be able to communicate with my laptop.

DEFINITION OF DONE

• [x] Research USB and UART
• [x] Design the circuit
• [x] Review and make improvements

DESCRIPTION

USB and UART

Going into this project I had no idea how my laptop communicated with a microcontroller, or even any USB devices.

I'm using a USB C connector just because that seems to be the trend with ESP32's.

Changes made for my design:

I researched the recommended USB to UART converter and found out that it had some issues with it. At work Dave found a "Basic USB to UART" converter that looks better than the old one. I decided to go with a similar and popular one on digikey linked below.

I added a DNP resistor between the USB shield and GND because connecting the USB shield directly to GND can sometimes cause problems (if the two don't exactly "agree" on what GND is).

I removed the 0 ohm resistors in the EN and BOOT buttons and added serial termination circuits to the input on the ESP32 because it can be helpful to "minimize reflections and improve the quality of the signal because it is split in two places".

I decided that I don't need the JTAG connector for debugging anything.

Circuit Design

USB to UART

Programming

Note: There is an LED connected to VBUS just to show it's plugged in.

NOTES

Digikey Links:

• Converter: FT231XS-R
• USB Connector: 2169900003
• The rest of the components will be picked out later as they aren't as big of a deal for the design. See #6.

SUPPORT

Introductory Sources:

• How does USB device discovery work? by Ben Eater
• How does a USB keyboard work? by Ben Eater
• PROTOCOLS: UART - I2C - SPI - Serial communications #001 by Electronoobs: First video I watched about all this and very helpful in understanding basic differences between everything.

All others:

• Why does ESP DevKit have 0Ω resistors for the TX and RX?
• Damping and Reflection Transfer with a Series Termination Resistor | Blog | Altium Designer
• When and Why to use termination resistors?
• USB Shield. To ground or not to ground?
• Where does 9600 bps come from?
• Here is why USB Type-C is AWESOME and how you can use Power Delivery for your electronics! by GreatScott!
• Parallel Termination Basics - Phil's Lab #119 by Phil's Lab (Part 1, didn't use parallel termination in my design)
• Series Termination Basics - Phil's Lab #121 by Phil's Lab (Part 2)

[austindriggs]

Might add a DNP serial connector just in case for good practice and because I have the room: SparkFun CH340C