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When I design a PCB that has a ESP32/ESP8266, I usually integrate a USB-UART bridge in the design as well. However, I am now working on a board that will likely have more than just a few copies.

The USB-UART bridge isn't necessary in this particular application as we are unlikely to edit the code once it is uploaded. It adds up to part cost and my time soldering the boards together.

I want to use one of those cheap USB TTL boards to program the boards.

There is a slight inconvenience.

The standard ESP32 auto program circuit uses the "Request to Send" (RTS) line, and the FTDI programmer that I want to use doesn't have that as a standard output as seen below.

enter image description here

It has an RTS pin on the side, so I could butcher the board and make an adapter on a breadboard but I am very sure my superiors won't accept such a put together solution.

Is there a possible hardware solution I could implement on the main board that would allow me to use one of these FTDI boards to program the ESP32 automatically? Pressing a button isn't an acceptable solution either. It has to be a plug in solution.

If there isn't any then I will have to design a separate programmer board that fits the requirements.

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You could use ESP-Prog which is built specifically for this job. Comes with both UART and JTAG as well, so it give's you more options. Comes with IDC cables so all you need is to add a small IDC connector to your board (similar to the ones on the ESP-PROG PCB)

It is not as cheap as those eBay FTDI clones but it still very cheap (~12$) and reliable.

ESP-PROG

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    \$\begingroup\$ I never have heard of this board before, you just save me a ton of time. Thank you! \$\endgroup\$ Commented Apr 2, 2021 at 13:04
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To upload code to a ESP8266 chip, you will need the circuit to have it in normal operation and expose RX,TX, IO0 and RST to any interface.

With that, you can use a programmer that will have the bridge circuit and make the proper connections.

As example, you can use a ESP-01(https://www.ebay.ca/itm/203337954357) or ESP-8285-01(https://www.ebay.ca/itm/203337940168)

Those modules do not have the programming circuitry and can be programmed by such devices like this

enter image description here

https://www.ebay.ca/itm/203304682591.

I like this one because it has all the circuitry to auto upload the code without having to press any button.

https://youtu.be/dMmxNos7V0o?t=49

But, if you are working with the bare ESP-12E/F families in your design, you should consider something like this

enter image description here

https://www.aliexpress.com/item/32991118728.html?spm=a2g0s.9042311.0.0.27424c4dfHrdsD

This one is good because you can just snap the module and it does have the circuitry for the upload of your code. I have one and it is a game changing

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