Send mac-addresses over Lora

Hi
I am aware that there are topics out there that partly cover this question, but even after a lot of trying and tinkering i was not able to achive my goal.

I try to transmit 2-3 BSSIDs from WiFi-APs with LoRa (TTN). I am able to extract the BSSID of nearby Wifis (WiFi.BSSIDstr(i) or WiFi.BSSID(i)).

In order to use the Function ttn.sendBytes() i need an array of bytes. But here comes the issue: I was not able to either loop over the BSSIDstr-return, remove the : and convert them, nor have i been able to concatenate WiFi.BSSID into one variable.

To be honest, i have an absolute mess between these variable-types. I come from php and ruby and do - even while trying hard - not understand what to use when…

I would be really happy if someone could give me a hint how to proceed!
Chris
p.s is there a “high-level” language available for esp32 that covers such kind of things? i tried to google it, but results were non-promissing

p. p.s., here’s my code. but actually, it does not really make sense to look at it. it’s really just try and error and every time i change something, it only gets worse :confused:

#include <TTN_esp32.h>
#include <WiFi.h>

const char* devAddr = "asdf"; // Change to TTN Device Address
const char* nwkSKey = "asdf"; // Change to TTN Network Session Key
const char* appSKey = "sadf"; // Change to TTN Application Session Key
RTC_DATA_ATTR int bootCount = 0;
uint8_t b[18]; // = {};
int i;


TTN_esp32 ttn ;

void printHex(uint8_t num) {
  char hexCar[2];

  sprintf(hexCar, "%02X", num);
  Serial.print(hexCar);
}

void setup() {
  Serial.begin(115200);
  ++bootCount;

}

void loop() {

  if (bootCount % 20 == 0) {
    //regular report
  } else {
    Serial.println("begin wifiscan");
    if (true) {
      String bssids = "";
      String a;
      int numberOfNetworks = WiFi.scanNetworks();
      if (numberOfNetworks > 1) {
        if (numberOfNetworks > 3) {
          numberOfNetworks = 3;
        }
        char cstr[6 * numberOfNetworks];
        int reslength = 12 * numberOfNetworks + 1;
        for (int i = 0; i < numberOfNetworks; i++) {
          a = WiFi.BSSIDstr(i);
          a.replace(":", "");
          bssids += a;          
Serial.println(WiFi.BSSIDstr(i));
          strcpy(cstr, bssids.c_str());
          ///Serial.println(cstr);
        }
        for (int y = 0; y < sizeof(bssids) / 2; y++) {
          //uint8_t tmp = sscanf(bssids.substring(0,2),"%x");
          //b[y] = (uint8_t)strtoul(cstr[0], NULL, 10);
        }
      }


      /*for (i = 0; i < sizeof(b); i++) {
        printHex(b[i]);
      }*/
      //ttn.sendBytes(b, 16);

    }
    delay(10000);
  }
}

can you provide a link to a description of the format of the data packet you are either receiving or transmitting, or are you just transceiving ascii data.

Well, i try to send up to 3 mac-addresses (BSSIDs) which are 6 bytes or 12 characters each. I’d like to concatenate these into one payload in order to save airtime and battery.

ttn.sendBytes seems to accept uint8_t as a datatype which i don’t really know how to fill with up to three WiFi.BSSID():

uint8_t payload[18];

What does the library you are using say about the sendBytes function, it could provide a clue …

are you asking about something like this? ??

#include <stdint.h>

#define MAC_SIZE    6

uint8_t mac1 [6];
uint8_t mac2 [6];
uint8_t mac3 [6];

uint8_t payload [3*MAC_SIZE];

void
prep (void)
{
    int i = 0;

    for (unsigned n = 0; n < MAC_SIZE; n++)
        payload [i++] = mac1 [n];

    for (unsigned n = 0; n < MAC_SIZE; n++)
        payload [i++] = mac2 [n];

    for (unsigned n = 0; n < MAC_SIZE; n++)
        payload [i++] = mac3 [n];
}

Well, thats one part (thanks a lot, this will for sure bring me forward).

But how to convert char into uint8_t? I tried looping over the char-array and do something like that, but this was / is still the main issue:

uint8_t b[18]; // = {};
for (int y = 0; y < sizeof(bssids) / 2; y++) {
  //uint8_t tmp = sscanf(bssids.substring(0,2),"%x");
  //b[y] = (uint8_t)strtoul(cstr[0], NULL, 10);
}

i know, it’s a mess :frowning:

what char? are you passing a MAC address as a string? (need to see)

uint8_t mac1 [6] = { 0xa5, 01, 02, 03, 04, 05 };

Thanks a lot. The last issue i was able to figure out myself. BSSID() is returning a pointer (?) and i had to use memcpy in order to store it in “your” mac1/2/3 var:

#include <TTN_esp32.h>
#include <WiFi.h>

const char* devAddr = "asdf"; // Change to TTN Device Address
const char* nwkSKey = "asdf"; // Change to TTN Network Session Key
const char* appSKey = "asdf"; // Change to TTN Application Session Key
uint8_t mac1 [6];
uint8_t mac2 [6];
uint8_t payload[12];
TTN_esp32 ttn ;

void prep(void)
{
  int i = 0;

  for (unsigned n = 0; n < 6; n++)
    payload [i++] = mac1 [n];

  for (unsigned n = 0; n < 6; n++)
    payload [i++] = mac2 [n];
}

void setup() {
  Serial.begin(115200);
  WiFi.scanNetworks();
  Serial.println(WiFi.BSSIDstr(0));

  memcpy(mac1,WiFi.BSSID(0),6);
  memcpy(mac2,WiFi.BSSID(1),6);

  prep();

  ttn.begin();
  ttn.personalize(devAddr, nwkSKey, appSKey);

  ttn.sendBytes(payload, sizeof(payload));
}

void loop() {}

Now i will have to build the main code around it, but that should be doable :slight_smile:

Thank you very much @gcjr !!

i don’t understand. are you saying these Keys are mac addresses?

No. Sorry for the confusion. These are just obfuscated TTN access-codes used in ttn.personalize()

WiFi.BSSID(i) returns the MAC of each Wifi found by WiFi.scanNetworks.

I will search for the three strongest or skip if less than 2 are closeby.

These macs will be sent over lora to an mqtt-client which will ask google location api where (approx) these wifis are. This makes a simple, (hopefully) power-efficient device which will help me find my stolen (or lost on a saturday night :-)) bike. In a more or less urban area this should be working quite well, but lets see in real life…

Thanks again for your help!
Chris

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