#Requesting Review for ELRS Gemini TX Custom PCB

10 messages · Page 1 of 1 (latest)

crystal basin
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Hi folks,

At my design team we've been working on making our own custom ELRS Gemini TX PCB, based on Jyesmith's design (https://oshwlab.com/jyesmith/expresslrs-gemini-tx). The goal was to implement the ELRS Gemini hardware and software in our own form factor to fit better in our drone's system, as well as to get a better understanding of the hardware, software, and PCB design through redesigning the PCB. We'd really appreciate a review of the schematics and PCB layout before we go ahead with ordering the board, if anyone is willing to review then please check out the attached PDF of the schematics & layout. Thanks everyone, and feel free to ask any questions about our design/system!

CC: @abstract totem @whole jasper

📎 ELRS_Gemini_TX.pdf
weary stump
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There's a weird bug with sharing reset lines between the two SX1280s, you should separate those or filter them. @sleek lodge was the one with the details as memory serves.

crystal basin
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Interesting, what exactly was the bug? I recall on the SX1280 datasheet that resetting each device is required before starting a SPI communication if there are multiple SX1280s on one SPI bus, so it seemed intuitive to have a shared reset line

weary stump
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It seems to be RF coupling onto that line resulting in bad SNR

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#hardware-dev message

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Apologies Jye could have sworn it was you talking about this. Either way, maybe something to put in your schematics?

crystal basin
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Appreciate the link, sounds good then shouldn't be a problem to make 2 separate resets

sleek lodge
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Hey guys 👋

Nice team you have 💪

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As MT has mentioned you should separate the RST lines. The target JSON has a define for rst2.

A couple of other minor things...

The MISO buffers are there to protect the sx1280 in case a Dev decided to accidentally use them at the same time. Just make sure they aren't too low, and the extra resistor on the esp32 miso won't be required. Same for the sck buffer.

You are making an internal module but also adding a usb bridge. Be careful with how these are connected with buffer resistors. The bridge may cause problems with normal Comms. But I see you have a header to individually select the connect. So you are probably ok.

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Being a university, please also give recognition to the ELRS project in any publications and presentation 🙂

A few of us are even current, or past, academics. We wouldn't mind being more involved if any publications came from this work. Personally, It's great CPD 😅