Flash ESP32 on Custom PCB from Tethered Burn Board

[shawnpatel]

I have a custom PCB with an ESP32, but I'm using an external burn board (https://www.amazon.com/gp/product/B07KP ... UTF8&psc=1) with the RX, TX, IOO, and EN pins tethered to my PCB via wires to flash my firmware. Below are the relevant portions of my schematic with the flashing infrastructure. Each (X) is an exposed pinout to connect the wires from the burn board.



I can't seem to get this setup working for some reason. Also, after trying this over a few attempts, I shorted two ESP32 modules. I'm not sure what could be the problem. I'm thinking that since my board and the burn board have differing voltage sources, this may be the issue. I've tried adding a common ground, but that didn't help either.

Any thoughts on what could be causing this are appreciated!

[Sprite]

You absolutely 100% certainly do need a common ground. Furthermore, what power source do you use?

[shawnpatel]

Thanks for the clarification on the common ground.

My circuit uses a 3.7v battery that is regulated to 3.3v to power the ESP32. The burn board is powered from the V_BUS of a micro USB input, which I presume is also regulated down to 3.3v.