Help with strings

BaartCM
Posts: 17
Joined: Tue Mar 13, 2018 11:55 am

Help with strings

Postby BaartCM » Fri Mar 30, 2018 7:13 pm

Hello,

This post is a request for help using painlessMesh, but it is to do with string manipulation above all else.

I am creating a character array of 65536 elements representing 32784 ADC readings.

The ADC read routine is

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rdg=analogRead(ADC0);
twf[a]=(char)encoder((int(rdg/64)));
twf[a+1]=(char)encoder((int(rdg%64)));
The loop increments by 2 each time.

As the ADC is 12 bits, I encode each value to 2 ascii characters using this function to ensure certain character values are avoided

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int encoder(int data){
  if (data < 52)
    return data + 40;
  else
    return data + 45;
}
This results in an array of ascii characters from 40 to 52 and 57 to 109 avoiding problematic characters in JSON.

I want to send the data in 128 packets of 512 characters using the painlessMesh library. So I need to put the first 512 characters into a String (followed by further 512 char packets) called pkt so I can send it out over WiFi using

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mesh.sendBroadcast(pkt);
I have tried using

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  for(a=0; a<512; a++)
    pkt[a]=twf[a];
  pkt[512]='\0';
with pkt declared as a String and the code compiles and runs but doesnt work. I have also tried the same declaring pkt as char[513] and char* but both of those have errors at compile time.

If I replace the above code with pkt = "Anything at all", it works and me seconde ESP32 reports an incoming message perfectly. Where am I going wrong?

Please help, Im going insane trying to work it out! Steve.

User avatar
kolban
Posts: 1683
Joined: Mon Nov 16, 2015 4:43 pm
Location: Texas, USA

Re: Help with strings

Postby kolban » Fri Mar 30, 2018 10:54 pm

When you say "String" ... do you mean String as in an Arduino environment? If so, this question might be best asked in the ESP32 Arduino forum?
Free book on ESP32 available here: https://leanpub.com/kolban-ESP32

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