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I drove the Ra-02 (SX1278) module with a 5V Nano, it's heating up and won't join

I drove the Ra-02 (SX1278) module with a 5V Nano, it's heating up and won't join

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Translated from Türkçe by AI ·

Hello, this is my second question 🙈My friends at the electronics club have a Basics Station gateway, connected to Hermetry. I wanted to send the garden soil moisture sensor over LoRaWAN too. I had an Arduino Nano (5V) and a Ra-02 module (it says SX1278 on it). I wired the SPI directly: D13 SCK, D12 MISO, D11 MOSI, D10 NSS, and the module’s VCC is on the Nano’s 3.3V pin.I tried OTAA with LMIC, the serial monitor keeps showing EV_JOINING, never EV_JOINED. Also, when I hold the module it feels warm, I don’t know if that’s normal. I added the device in Hermetry, but nothing shows up in the frames log.Are the SX1278’s SPI pins 5V tolerant? Do I need a level shifter?

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Translated from Türkçe by AI ·

It is not robust. The digital inputs of the SX127x are rated at most around VDD + 0.3 V. Driving it with a 5V signal slowly kills the module, and the heating may be caused by that.

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Translated from Türkçe by AI ·

Automatic level shifters like TXS0108 sometimes cause problems on SPI, I use a 74LVC245 or a resistor divider. Cleaner is a 3.3V board.

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Ra-02 is 433 MHz, right? Which band is the gateway on?

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I don’t know, I think it says 433 on the box. The gateway was set up by friends, I’ll ask them.

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AyÅŸe caught it, that’s the real issue. There are two things.Frequency: The Ra-02 is a 433 MHz module. On Hermetry the frequency plan is determined by the gateway, so if your friends’ gateway is on 868, the device also needs to be EU868. The join request sent on 433 is not heard by anyone, which is why the frames log is empty. Even if you fix the level shifting, you won’t join with this module.Voltage: As Büşra said, there’s no driving at 5V. I would do it this way: an 868 MHz SX1276 module (the RFM95W 868 version is common) and a 3.3V board. An ESP32 works, and so does a 3.3V Pro Mini. That way you don’t need a level converter. If it’s something battery-powered like a soil moisture sensor, the Pro Mini draws less current.On the Hermetry side, add the device as Class A, OTAA. In LMIC, select the EU868 region (CFG_eu868 in lmic_project_config.h), and pay attention to the byte order of DevEUI and AppEUI: LMIC wants LSB, AppKey wants MSB. Everyone gets stuck there on the first try.Regions and channels are here: Bölgeler ve frekans planları

Accepted solution♥ 7

Translated from Türkçe by AI ·

I asked around, and the gateway is 868. I got an RFM95W 868 and a 3.3V Pro Mini, and selected CFG_eu868. I had also typed the DevEUI backwards, and after correcting it the second attempt gave EV_JOINED, and the join shows up in the frames log. The old Ra-02 has probably really burned out too, it doesn’t respond at all anymore 😅

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