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Does the LILYGO TTGO T-Beam V1.1 have Bias-t DC protection in the input? #156

Closed stephenmorton closed 2 years ago

stephenmorton commented 2 years ago

I have a LILYGO TTGO T-beam V1.1 ESP32 433MHz module.

I plugged one of these (https://www.nooelec.com/store/lana.html) in with what I thought was a DC block barrel between LNA and T-Beam board. I found out the barrel I used wasn’t a DC block, so I am wondering, if the LILYGO TTGO will still be OK or not (does it have DC protection). I only plugged it in for around 5 minutes, until I realised.

I did find the schematic for the board here (https://github.com/Xinyuan-LilyGO/LilyGo-LoRa-Series/blob/master/schematic/LilyGo_TBeam_V1.1.pdf) and noticed it has a series and a parallel cap going to ground. I'm assuming this is here for protection, but might be for coupling.

I am using the board to receive weak signals from satellite, and so far I haven't had much luck. I doubt it would have damaged the board, especially for the short time I had it plugged in. I only used 5V on the LNA, so the voltage presented to the T-beam would be less than that. Anyway, thought I would check, I bet someone here would probably know.

Regards,

stephenmorton commented 2 years ago

For anyone who is interested, it seems the brief time I had the LNA (nooelec LaNA) plugged in, without a DC block, didn't appear to damage the TTGO board. I am not 100% sure the LNA pushed out DC (although the docs I read on it seem to indicate that it does push out DC on the output port), but until I can do more testing, I'll be safe and add a DC block between it and the TTGO in future.