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Xinyuan-LilyGO / TTGO-T-Display

MIT License
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270pF capacitors between 36 - 37 and 38 - 39 GPIOs #48

Open ddosoff opened 3 years ago

ddosoff commented 3 years ago

Hello LiLyGO,

Today discovered that I can't use SPI_MISO on GPIO 38 and UART RX on GPIO 39 simultaneously. I checked https://github.com/Xinyuan-LilyGO/TTGO-T-Display/blob/master/schematic/ESP32-TFT(6-26).pdf and found capacitors between 39, 38 and 37, 36 GPIOs.

Selection_002

Please describe what purpose of this capacitors?

ddosoff commented 3 years ago

Is it possible to remove them from PCB?

bradanlane commented 3 years ago

Thanks @ddosoff - I didn't catch this on my project. I've gone ahead and removed those CAPs.

I hope we get an answer as to their intended function.

tadam777 commented 3 years ago

There's no information about their role in the ESP32 datasheet, but they've got a short description in the ESP32 hardware design guidelines : 2021-01-31 14_51_51-esp32_hardware_design_guidelines_en pdf - Adobe Acrobat Pro DC

T1j3ff commented 2 years ago

My guess is these have a role in touch sensitive switch .. But not shure how

tadam777 commented 2 years ago

I found an article about these capacitors, they're related to an LNA (low noise amplifier) that's actually included on the ESP32, but didn't work well so it was simply removed from the documentation, even if it still exists in the chip.

Someone took the version 1 of the documentation (where it was still described) to find out how to use it.

Full story here : https://github.com/krzychb/esp32-lna And detailed operation here : https://github.com/krzychb/esp32-lna/blob/master/docs/lna-operation.md