SX127X not accepted in TTN for the first 10 minutes

Hi Guys,
I have some problems with my project. I just want to make my new module SX1276x works with TTN when I put the power :wink: It is for outdoor low-cost and low-power sensors.


I usually work with RN2483, but it’s very difficult to find it right now, so I went for SX127x (I asked to the community on this post : Best LoRa chip for Arduino & TTN - #5 by bluejedi)

I used the MCCI Arduino LoraWAN Library, apparently it’s the best one. It’s this one :


I didn’t forget to edit arduino-lmic/project_config/lmic_project_config.h in order to be used in Europe :

// project-specific definitions
#define CFG_eu868 1
#define CFG_sx1276_radio 1

I also created an End-device on TTN website, using OTAA activation.
I pasted the DevEUI, AppEUI, AppKey in my code (which is the ttn-otaa). I had to pay attention to msb / lsb format).

Then, I plugged my module to an Arduino pro mini 3.3V.

Here is the schema, I used it from the post Error: MCCI_LoRaWAN_LMIC_library-3.0.99\src\lmic\oslmic.c:53 - #8 by WSA2021 :


I was hoping to receive directly the data, but I had this on the serial monitor

Packet queued
278150: EV_TXSTART
671431: EV_JOIN_TXCOMPLETE: no JoinAccept
4730386: EV_TXSTART
5123670: EV_JOIN_TXCOMPLETE: no JoinAccept
8928049: EV_TXSTART

And this on TTN :


After 10min of looking for a pin problem or soft problem, I’ve noticed that it was working without doing anything… :face_with_raised_eyebrow:


20964984: EV_TXSTART
21361484: EV_JOIN_TXCOMPLETE: no JoinAccept
28537921: EV_TXSTART
28934419: EV_JOIN_TXCOMPLETE: no JoinAccept
36160375: EV_TXSTART
36501799: EV_JOINED
netid: 19
devaddr: 260BB4F8
AppSKey: 3C-B2-0B-51-62-1E-DA-EF-17-65-7B-6F-B8-BE-B1-B6
NwkSKey: 5E-0C-C0-59-C8-23-C6-73-6D-CE-32-70-9F-F9-AA-CF
36509021: EV_TXSTART
36841618: EV_TXCOMPLETE (includes waiting for RX windows)
37538782: EV_TXSTART
37925998: EV_TXCOMPLETE (includes waiting for RX windows)
39176637: EV_TXSTART
Packet queued
39563927: EV_TXCOMPLETE (includes waiting for RX windows)
40814563: EV_TXSTART
Packet queued
41201943: EV_TXCOMPLETE (includes waiting for RX windows)
42452579: EV_TXSTART
Packet queued

I really don’t understand why !

Here is my code, it is just the ttn-otaa from the library, I only changed the keys and the payload.
Do you guys have any idea ?
Thank you so much,

 * Copyright (c) 2015 Thomas Telkamp and Matthijs Kooijman
 * Copyright (c) 2018 Terry Moore, MCCI
 * Permission is hereby granted, free of charge, to anyone
 * obtaining a copy of this document and accompanying files,
 * to do whatever they want with them without any restriction,
 * including, but not limited to, copying, modification and redistribution.
 * This example sends a valid LoRaWAN packet with payload "Hello,
 * world!", using frequency and encryption settings matching those of
 * the The Things Network.
 * This uses OTAA (Over-the-air activation), where where a DevEUI and
 * application key is configured, which are used in an over-the-air
 * activation procedure where a DevAddr and session keys are
 * assigned/generated for use with all further communication.
 * Note: LoRaWAN per sub-band duty-cycle limitation is enforced (1% in
 * g1, 0.1% in g2), but not the TTN fair usage policy (which is probably
 * violated by this sketch when left running for longer)!

 * To use this sketch, first register your application and device with
 * the things network, to set or generate an AppEUI, DevEUI and AppKey.
 * Multiple devices can use the same AppEUI, but each device has its own
 * DevEUI and AppKey.
 * Do not forget to define the radio type correctly in
 * arduino-lmic/project_config/lmic_project_config.h or from your BOARDS.txt.

#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>

// For normal use, we require that you edit the sketch to replace FILLMEIN
// with values assigned by the TTN console. However, for regression tests,
// we want to be able to compile these scripts. The regression tests define
// COMPILE_REGRESSION_TEST, and in that case we define FILLMEIN to a non-
// working but innocuous value.
# define FILLMEIN 0
# warning "You must replace the values marked FILLMEIN with real values from the TTN control panel!"
# define FILLMEIN (#dont edit this, edit the lines that use FILLMEIN)

// This EUI must be in little-endian format, so least-significant-byte
// first. When copying an EUI from ttnctl output, this means to reverse
// the bytes. For TTN issued EUIs the last bytes should be 0xD5, 0xB3,
// 0x70.
static const u1_t PROGMEM APPEUI[8]={ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
void os_getArtEui (u1_t* buf) { memcpy_P(buf, APPEUI, 8);}

// This should also be in little endian format, see above.
static const u1_t PROGMEM DEVEUI[8]={ 0xF6, 0xB1, 0x04, 0xD0, 0x7E, 0xD5, 0xB3, 0x70 };
void os_getDevEui (u1_t* buf) { memcpy_P(buf, DEVEUI, 8);}

// This key should be in big endian format (or, since it is not really a
// number but a block of memory, endianness does not really apply). In
// practice, a key taken from ttnctl can be copied as-is.
static const u1_t PROGMEM APPKEY[16] = { 0xFB, 0x0C, 0xC6, 0xC9, 0x38, 0x56, 0xE7, 0x44, 0x5B, 0xF4, 0xFE, 0xDC, 0xA0, 0x8A, 0x2A, 0xE5 };
void os_getDevKey (u1_t* buf) {  memcpy_P(buf, APPKEY, 16);}

static uint8_t mydata = 0;
static osjob_t sendjob;

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL = 20;

// Pin mapping
const lmic_pinmap lmic_pins = {
    .nss = 10,
    .rxtx = LMIC_UNUSED_PIN,
    .rst = 5,
    .dio = {2, 3, LMIC_UNUSED_PIN},

void printHex2(unsigned v) {
    v &= 0xff;
    if (v < 16)
    Serial.print(v, HEX);

void onEvent (ev_t ev) {
    Serial.print(": ");
    switch(ev) {
        case EV_SCAN_TIMEOUT:
        case EV_BEACON_FOUND:
        case EV_BEACON_MISSED:
        case EV_BEACON_TRACKED:
        case EV_JOINING:
        case EV_JOINED:
              u4_t netid = 0;
              devaddr_t devaddr = 0;
              u1_t nwkKey[16];
              u1_t artKey[16];
              LMIC_getSessionKeys(&netid, &devaddr, nwkKey, artKey);
              Serial.print("netid: ");
              Serial.println(netid, DEC);
              Serial.print("devaddr: ");
              Serial.println(devaddr, HEX);
              Serial.print("AppSKey: ");
              for (size_t i=0; i<sizeof(artKey); ++i) {
                if (i != 0)
              Serial.print("NwkSKey: ");
              for (size_t i=0; i<sizeof(nwkKey); ++i) {
                      if (i != 0)
            // Disable link check validation (automatically enabled
            // during join, but because slow data rates change max TX
	    // size, we don't use it in this example.
        || This event is defined but not used in the code. No
        || point in wasting codespace on it.
        || case EV_RFU1:
        ||     Serial.println(F("EV_RFU1"));
        ||     break;
        case EV_JOIN_FAILED:
        case EV_REJOIN_FAILED:
        case EV_TXCOMPLETE:
            Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
            if (LMIC.txrxFlags & TXRX_ACK)
              Serial.println(F("Received ack"));
            if (LMIC.dataLen) {
              Serial.print(F("Received "));
              Serial.println(F(" bytes of payload"));
            // Schedule next transmission
            os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(TX_INTERVAL), do_send);
        case EV_LOST_TSYNC:
        case EV_RESET:
        case EV_RXCOMPLETE:
            // data received in ping slot
        case EV_LINK_DEAD:
        case EV_LINK_ALIVE:
        || This event is defined but not used in the code. No
        || point in wasting codespace on it.
        || case EV_SCAN_FOUND:
        ||    Serial.println(F("EV_SCAN_FOUND"));
        ||    break;
        case EV_TXSTART:
        case EV_TXCANCELED:
        case EV_RXSTART:
            /* do not print anything -- it wrecks timing */
        case EV_JOIN_TXCOMPLETE:
            Serial.println(F("EV_JOIN_TXCOMPLETE: no JoinAccept"));

            Serial.print(F("Unknown event: "));
            Serial.println((unsigned) ev);

void do_send(osjob_t* j){
    // Check if there is not a current TX/RX job running
    if (LMIC.opmode & OP_TXRXPEND) {
        Serial.println(F("OP_TXRXPEND, not sending"));
    } else {
        // Prepare upstream data transmission at the next possible time.
        LMIC_setTxData2(1, mydata, sizeof(mydata)-1, 0);
        Serial.println(F("Packet queued"));
    // Next TX is scheduled after TX_COMPLETE event.

void setup() {

    #ifdef VCC_ENABLE
    // For Pinoccio Scout boards
    pinMode(VCC_ENABLE, OUTPUT);
    digitalWrite(VCC_ENABLE, HIGH);

    // LMIC init
    // Reset the MAC state. Session and pending data transfers will be discarded.

    // Start job (sending automatically starts OTAA too)

void loop() {

Was this a one time test or is it consistent (aka scientific).

How far apart is your gateway from your device? Less than 5m & a brick wall is BAD.

I did it 3 times, I always have to wait approx 12min to have my first payload received. My Gateway is on the top of my building, I’d say 20meters :slight_smile:

MCCI v0.9.1 looks pretty old.
Not sure where that version number comes from but the latest release on GitHub is v4.1.1.

For your Pro Mini with SX1276 module you may try the following:

For the Pro Mini LMIC-node uses an older (now deprecated) version of LMIC.
The combination of LMIC-node with MCCI LMIC does not fit on the Pro Mini due to limited available memory on the ATmega328. For more modern 32-bit MCU’s LMIC-node will use MCCI LMIC instead.

While this will not use MCCI LMIC for your board you can still use it for testing your setup and check if the problem then still occurs or not (at all).

For required wiring check and the BSF file for the Pro Mini.

1 Like

Hi @bluejedi, thank you for the tips : I’ve downloaded the v0.9.1 from the arduino IDE.
The Github your are taking about, is it a library like others in arduino ? because I cannont success to install it by just download the zip, as usual…

So you are saying that it is not possible to make it work on my mini pro ? Sorry I’m a bit confused about LMIC-node, MCCI LMIC etc… ^^

Thank you,

Sorry I just read the documentation, I need Platform IO on VS.
I did the modifications on the files, I think I’m a bit lost now with ‘the code to compile’.
But I’ll try a bit more as it’s just new :wink:


Dear ​simmoinard,
I’m not an expert, but maybe this gonna help. I wasn’t using arduino board, but ATmega328 on breadboard with 8MHz internal clock and this didn’t work. I had to switch to 16MHz crystal. I had to add
LMIC_setClockError(MAX_CLOCK_ERROR * 3 / 100);
LMIC.dn2Dr = DR_SF9;

in sketch after LMIC_reset();

You can make sure that installed MCCI LoRaWAN LMIC library not MCII Arduino LoRaWAN library

MCCI LoRaWAN LMIC library is in Arduino library manager in 4.1.1 version

Thank you so much @shutdownsystem !!
The first line make it works. I’m losing some packages, but I expect to have a bad antenna on my node. Will try with a new one.

For information, do you know what is the function .dn2Dr ? and setDrTxpow ?
Because I also wanted to put the SF to 10, I guess it’s with those two functions… (And alsowhat is the 17 in setDrTxpow)

Read some documentation to answer your questions :stuck_out_tongue:
I used this library just to confirm that my setup works.

About the antenna, check this and watch this.
I built this by my own, it’s dirty cheap, one connector from local store for about 2$ and some copper wire. Works so much better that 10$ antenna that I bought. (But be accurate as possible, take your time)