# What is the maximum number of characters I can send with LMiC? **URL:** \ **Category:** LMIC\ **Created:** [September 16, 2017, 12:08am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537 "2017-09-16T00:08:00Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![pierrot10](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/pierrot10/32/44794_2.png) [@pierrot10](https://www.thethingsnetwork.org/forum/u/pierrot10)\ **Post date:** [September 16, 2017, 12:08am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/1 "2017-09-16T00:08:00Z")
Good day! I am new with TTN and there is one small thing I do not understand with byte. I am working with that exemple [https://github.com/mikenz/LoRa-LMIC-1.51/blob/master/examples/nano-lmic-v1.51-F/nano-lmic-v1.51-F.ino#L98](https://github.com/mikenz/LoRa-LMIC-1.51/blob/master/examples/nano-lmic-v1.51-F/nano-lmic-v1.51-F.ino#L98) the variable mydata store the message to be sent. I know that the message must be smal as possible, I am collecting sensors values. I have 10 sensors and it would be fine to have one record, at TTN console, for one loop of measurement. I means all sensors values by record. I am not sure 1. How many caracters I can save into mydata because of the 64 2. **and, first all, can I enlarge the value of 64, and if yes, what is the limit?** How many bits take one caracter? One? So if one byte have 8 bits, I can have 8 carcaters in one bytes, I can have 512 caracters in my variable mydata. That’s correct? I am sorry for my basic question, but I mainly would like to know if I can enlarge mydata[64], if needed? Many thank for your help Cheers ---
**Author:** ![arjanvanb](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/arjanvanb/32/46626_2.png) [@arjanvanb](https://www.thethingsnetwork.org/forum/u/arjanvanb)\ **Post date:** [September 16, 2017, 9:21am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/2 "2017-09-16T09:21:11Z")
You should not think in characters, but only in bits and bytes. See [Working with Bytes](https://www.thethingsnetwork.org/docs/devices/bytes.html) in the documentation and learn that `strcpy((char *) mydata,"{\"Hello\":\"World\"}");` in your example code is bad practice. When you understand bits and bytes, the `uint8_t mydata[64]` in the example won’t be your problem: increasing that will make your own code compile just fine. However, the LMiC library you’re using has a limit of 51 bytes (totalling to 64 bytes when including the 13 bytes LoRaWAN headers). So without modification of that library, even using all 64 bytes in `uint8_t mydata[64]` will already fail as that would exceed the 51 bytes LMiC can send. To increase the maximum size in the libraries, see [LMiC fails to send application payload larger than 51 bytes](https://www.thethingsnetwork.org/forum/t/lmic-fails-to-send-application-payload-larger-than-51-bytes/8923) and [https://github.com/matthijskooijman/arduino-lmic/issues/100](https://github.com/matthijskooijman/arduino-lmic/issues/100). But still then, in many (or all) regions, **the maximum payload size is 51 bytes for SF12, so trying to go beyond that might be futile**. The good news: I doubt each of your 10 sensors needs a lot of bytes for its measurements. If only few need, say, 6 bytes and most just need 1 or 2 bytes, or even just half a byte or a single bit, then the total result will probably fit just fine. For an example of combining a 4 bits and 12 bits value into 2 bytes, see [here](https://www.thethingsnetwork.org/forum/t/arduino-pro-mini-lmic-otaa-with-multi-channel-gateway/9400/8). ---
**Author:** ![pierrot10](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/pierrot10/32/44794_2.png) [@pierrot10](https://www.thethingsnetwork.org/forum/u/pierrot10)\ **Post date:** [September 16, 2017, 9:48am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/3 "2017-09-16T09:48:38Z")
Thank a lot for your reply. I am going to read your link and reconsider my code followinf your comment. But for you, I still do not how large (maximum) should be my json string to fit in mydata. I red, that I should not send a json form fomart and I will change it, but has my sensor meseaurement return my a double and I convert it to a char, I need to how how many value (caracters) I can sent. a caracter take one or some bits, no? Have a nice day and tank for your help ---
**Author:** ![arjanvanb](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/arjanvanb/32/46626_2.png) [@arjanvanb](https://www.thethingsnetwork.org/forum/u/arjanvanb)\ **Post date:** [September 16, 2017, 9:52am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/4 "2017-09-16T09:52:14Z")
> [@pierrot10](#): > > I still do not how large (maximum) should be my json string to fit in mydata > [@pierrot10](#): > > my sensor meseaurement return my a double and I convert it to a char The answer is in “Working with Bytes”. After reading that, never, ever think about sending human-readable data again. And when not convinced, read [Limitations: data rate, packet size, 30 seconds uplink and 10 messages downlink per day Fair Access Policy](https://www.thethingsnetwork.org/forum/t/limitations-data-rate-packet-size-30-seconds-uplink-and-10-messages-downlink-per-day-fair-access-policy/1300). Now, go read! ---
**Author:** ![pierrot10](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/pierrot10/32/44794_2.png) [@pierrot10](https://www.thethingsnetwork.org/forum/u/pierrot10)\ **Post date:** [September 16, 2017, 10:15am UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/5 "2017-09-16T10:15:07Z")
Thank a lot for your reply. Sure, I will change my message and make sure , it is byte and not a human-readable value but I atill confuse about the convertion of my double value or char value to a bits/byte But, the thing which still troube me. If I print `Serial.println(mydata)` my terminal return me an error. > exit status 1 > call of overloaded ‘sprintln(uint8\_t [64], int)’ is ambiguous However, if I print `Serial.println((char *)mydata);` it print me an human-raedable value. So does mydata value are already in bytes (no human-redable)? because (char \*) should convert in readable value, no? Morever, mydata is declare in this way `uint8_t mydataAll[64];` But for sure, I have to review this part of my code (and remove the ’ {}:" ’ which consist of a json format Tnank a lot ---
**Author:** ![arjanvanb](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/arjanvanb/32/46626_2.png) [@arjanvanb](https://www.thethingsnetwork.org/forum/u/arjanvanb)\ **Post date:** [September 16, 2017, 12:27pm UTC](https://www.thethingsnetwork.org/forum/t/what-is-the-maximum-number-of-characters-i-can-send-with-lmic/9537/6 "2017-09-16T12:27:48Z")
> [@pierrot10](#): > > `Serial.println((char *)mydata);` > > it print me an human-raedable value. In computer memory and when transmitting, everything is just a sequence of bits (and 8 bits are then called a byte). That might be hard to understand at first, but you’ll need to read and re-read “Working with Bytes” (and the links it refers to) until you do understand. When you think you understand, you should be able to see: - When (erroneously) using human-readable text, the value 34.51: - [is stored as](http://www.binaryhexconverter.com/ascii-text-to-binary-converter) the 48 bits `00110011 00110100 00101110 00110101 00110001 00000000` which includes a trailing NUL-character for a [null-terminated string](https://en.wikipedia.org/wiki/Null-terminated_string), - which is the same the decimal [ASCII codes](http://www.rapidtables.com/code/text/ascii-table.htm) 51, 52, 46, 53, 49 and 0, - which [is the same as](http://www.binaryhexconverter.com/ascii-text-to-hex-converter) hexadecimal `0x33 34 2E 35 31 00`, - and further below you’ll see that using `Serial.println((char *)mydata)` will show “34.51” for the above ASCII codes. - When (nicely) using an integer number, the value 34.51 can be multiplied by 100 to get 3451, which: - [is stored as](http://www.binaryhexconverter.com/decimal-to-binary-converter) the 16 bits `00001101 01111010`, - which [is the same as](http://www.binaryhexconverter.com/decimal-to-hex-converter) `0x0D 7B`, - and (erroneously) using `Serial.println((char *)mydata)` might then print a new line (for ASCII code `0x0D`) followed by `{` (for `0x7B`), followed by whatever is in memory until it finds the first `0x00` NUL-character, meanwhile printing garbage for all bytes that cannot be converted to ASCII. Using the `(char *)mydata` above you’re telling the compiler that the program _knows_ that what is currently in the memory buffer `mydata` is in fact human-readable text (and not, for example, some image, or a PDF document, or a simple number). The only reason the program knows, is because it has stored the value there itself (like by using `strcpy` earlier). So, `(char *)` does not _convert_ anything; it _is_ already human-readable text in memory. And when trying to use a built-in function such as `Serial.println` to show its contents, then your program needs to share that knowledge with the compiler, by prefixing `mydata` with `(char *)`. (Here, `(char)` tells the compiler it’s human-readable text, and `*` gives the compiler a “pointer” to the memory location, which is simply what `Serial.println` expects.) That line would then print garbage if it was in fact not human-readable text. But as it apparently shows the value you expected, you’re still storing human readable text in memory (and so you would also be sending that to TTN). > [@pierrot10](#): > > I have to review this part of my code (and remove the ’ {}:" ’ which consist of a json format Just removing the `{...}` does not suffice. JSON is one of the many human-readable formats. Changing `{"x": 123.45, "y": 45.678}` into, e.g., `123.45,45.678` would still be a human-readable format, wasting bytes when sending to TTN.