topic Re: Labview + xbee read sensor, uncoding the hex string in LabVIEW

Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 10:43:16 GMT

Hey guys 🙂

Before i start i apologize for my bad English, i'm a student in Portugal in Eng. of Eletronics and Computers, and i have this last project to make, while working on an interprize here in Portugal that manufacters eletronic components for cars, home machines, etc.

Without going into much details that doesnt matter, my project is basicly read some valors from some sensors, and send that data with xbee to the Labview, so i can manage to register every data, and later make warnings about it, cause those sensors are currently used to control and monotorize one line of machines that use a lot of liquids with diferent temperatures and pH

Right now i'm just using the DS18B20 sensor from One-Wire, just to make things simple
I've manage to put the code on the arduino, that is connected to my xbee label as router AT (transmitter), and i have another xbee connected with my pc, label as coordinator API (receiver of information).

I've already managed to configured the 2 xbees with no problem, and they are currently passing info from one to another, as i show you in the pic of x-ctu.
I even managed to read the data on the Labview
my real problem now is that i dont really have a clue how to parse the string, or divide it so i can read only the valors that i need, in this case, temperature valours. As i hope you are familiar, the xbees send their data em Hex or ASCII code (correct me if i'm wrong but those are the ones i'm getting), and so my string kinda starts with a start byte (7E) so i managed to find the beggining and ending of my string sended, and even managed to identify the Hex code that holds the information of the valours of temperature received.

My real real issue is how to manipulate the string, so i can pull only the data i want (temperature numbers) and discard all the rest.

Here i'll send you some shots, my currently VI.
If you need any more details, like the configuration of the xbees i can provide it, although i dont think its relevant since they are working fine.

cheers to all!

Re: Labview + xbee read sensor, uncoding the hex string

LV_Pro — Tue, 22 Apr 2014 14:15:27 GMT

Is the area in green the data you want? Does it always come in the same place in the data string?

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 14:35:04 GMT

Yes, it always come in the same location, i'll try to explain here:

the code for 1 reading is like this one

7E 00 13 90 00 13 A2 00 40 A2 3A 63 C0 DD 01 32 32 2E 36 39 0D 0A 85

this is received in labview as ASCII code, so basicly the information i want is the 32 32 2E 36 39, that corresponds to 22.69 for example (its the valor of my temperature). basicly 2 numbers for each character in ASCII code

but if i right click on the buffer (string readed) and change the mode to Hexadecimal it appears to me like this:

7E00 1390 0013 A200 40A2 3A63 C0DD 0132 322E 3639 0D0A 85

and i'm afraid that without the spaces it may even damage my information

what i really want is to learn how to clear everything else but those 5 pairs of numbers

from 7E00 1390 0013 A200 40A2 3A63 C0DD 0132 322E 3639 0D0A 85, extract this: 32 32 2E 36 39 and convert it to: 22.69

thanks in advance for you time, if you need more details please tell me so I can provide it the best way i can

🙂

Re: Labview + xbee read sensor, uncoding the hex string

Omar_II — Tue, 22 Apr 2014 14:35:10 GMT

Get rid of the Bytes at Port and rely on the Termination Char. Your device seems to end each message with x0D x0A (Chairage Return/Line Feed). Use the default Termination Char (x0A) to only read in one complete line at a time.
You are checking the string after the Feed Back node so you are only rechecking the beginning of the srting. Rechecking same OLD first line each time and not the NEWEST line. Check the string that is returned from the VISA read.
Init the Feed Back Node to an empty string or each time you run it the old data will still be there.
Will the temperture ALWAYS be in the XX.XX form? What does the xbee manual say? Does the xbee manual tell you if there is information in the message telling you how many digits are used to send the temperture? What happens if the temper is over 99.99 or under 10.00? Like 100.00 or 9.99?

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 14:37:56 GMT

Also, i forgot to mention

since its in a while cycle it continues to read the valors, so i also need to find a way to stop it, or do a reading, register it into something (an array would be great, but since i cant even extract nothing from it, dont know how to do it), clear the buffer, and do the reading again

the final propuse of the program is to do 1 reading per minute for example, from the sensor that flows trough the xbee

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 14:43:22 GMT

First of all, thanks again for the great help 🙂 you rock mate!

as for the type of reading of the temperature, yes it does always comes like XX.XX, at valors like 9.99, it would be displayed like 09.99, again, always like XX.XX. as for the 100.00 dont worry about it, the place where i'm working would only reach a max temperature reading of 75-80ºC.

And yes, it will always be as XX.XX

this kind of reading is from my program in arduino that is connected to my xbee router AT. I can change it to only have 1 decimal number, or even more than 3, so it would be like XX.X or XX.XXX doesnt matter, because the xbee only codes like 1 number or char at a time in ASCII code, so for each number it will always have a XX code

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 14:45:30 GMT

the part of my VI that displays those elements, it was my failed atempt to check the index of the string (as if it was an array) to pull the numbers i did want

Re: Labview + xbee read sensor, uncoding the hex string

Dennis_Knutson — Tue, 22 Apr 2014 14:47:17 GMT

A simple String to Byte Array can be used. If you use a termination character, the read will automatically terminate, you will read the entire data that is transmitted, the buffer will be cleared.

p.s. The word is values, not valors.

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 14:56:04 GMT

Thanks for the help, learning everyday :)!

the problem to make a terminal char at the end of beginning of the information i want, and pull it out with a string, is that it cant be modified within the xbee, the xbee creates its own type of string ( xx xx xx xx xx... and so on), the last byte is always called the checksum, right before those 2 pairs of values that you spoke, but even it seems to change, and it should not (thats what the manuals say, so not sure of it)

but i'll try to do something more, thanks again for everything

Re: Labview + xbee read sensor, uncoding the hex string

Omar_II — Tue, 22 Apr 2014 14:57:24 GMT

@Raknugar wrote:

7E 00 13 90 00 13 A2 00 40 A2 3A 63 C0 DD 01 32 32 2E 36 39 0D 0A 85

0D 0A marks the end of the message. 85 is the start of the next message.

@Raknugar wrote:

but if i right click on the buffer (string readed) and change the mode to Hexadecimal it appears to me like this:

7E00 1390 0013 A200 40A2 3A63 C0DD 0132 322E 3639 0D0A 85

and i'm afraid that without the spaces it may even damage my information

The spaces are not really there. The spaces are only in the display and not in your string. The spaces are only there to make it easier for YOU to read them.

Re: Labview + xbee read sensor, uncoding the hex string

Dennis_Knutson — Tue, 22 Apr 2014 15:03:13 GMT

It seems unusual to append the checksum after a cr/lf but you can still use the termination character. Just read a single byte after the read where you get the values.

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 15:06:47 GMT

Thanks Omar 🙂

i was stupid, didnt checked that Dennis already had a soluction for extracting my value xD

thanks for everything 🙂

Just a last question
if i were to add another information in my string, after the numbers, just a char (S or N, its for another sensor), the process is the same?

since its a character and not a number, how should i work with that?

you guys here are amazing, i should had come to the forums earlier 🙂

Re: Labview + xbee read sensor, uncoding the hex string

Dennis_Knutson — Tue, 22 Apr 2014 15:14:54 GMT

The process should be the same. If, for example, you use String to Byte Array, you could use index array, a Byte Array to String with a typecast or flatten to string, join numbers with a typecast/flatten, etc. It would be helpful if you attached an image that shows the data in normal display. You might just need String Subset function.

Re: Labview + xbee read sensor, uncoding the hex string

Omar_II — Tue, 22 Apr 2014 15:16:22 GMT

@Raknugar wrote:

Also, i forgot to mention

since its in a while cycle it continues to read the valors, so i also need to find a way to stop it, or do a reading, register it into something (an array would be great, but since i cant even extract nothing from it, dont know how to do it), clear the buffer, and do the reading again

the final propuse of the program is to do 1 reading per minute for example, from the sensor that flows trough the xbee

How often does the YOUR device send you a message? If you wish to only take a reading once a minute, you will need to flush out old messages from the com port input buffer to be sure you are read the latest reading. Then you have to problem of reading in a partial message.

It would be best to keep reading all messages as they are send to stay in sync (in step) with your device and just throw away readings you do not want to keep.

Re: Labview + xbee read sensor, uncoding the hex string

Omar_II — Tue, 22 Apr 2014 15:26:17 GMT

@Raknugar wrote:

Thanks Omar 🙂

i was stupid, didnt checked that Dennis already had a soluction for extracting my value xD

The value xD is the ASCII code for "Carriage Return". What you get along with xA to mark the end of a line. I don't think it is part of you data.

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 15:40:09 GMT

Hey guys again 🙂

i intent to send information to labview once a minute, but i'll do modifications in the arduino (my MCU) to have a delay of 1min with each reading, so its simple, and dont need to make modifications in the labview. but if there somekind of timercount to display information in labview??

also Dennis, thanks again for helping me with the strings control, unfortonatly i dont have the material with me to test it.
I will have a indutive sensor, to monitor the speed of a motor, and for example, if the velocity is lower than whats expected within one minute (rotations per minute) i will say he is stopped (S for stop, N for non-stop), Thats why i asked
my final project would be like, display temperature, velocity of the motor (rpm) and if its stopped or not (maybe put a led on/off for it)

thats why my issue was to know how could i separate information

since it will come in the type of xx xx xx xx xx xx like we talk about

it would be like xx xx xx xx xx YY YY . YY YY SS RR RR RR xx xx

where yy yy . yy yy (its my actual 22.69 values), SS would be the information in ASCII code of the char for turned on or off (S or N) and RR is the value for rotations for minute (3 values, cause my motor wont reach more than 1000 rpm)

Am i clear enough? i'm sorry if my english sometimes is confused, i never was the best student in English classes (too much girls to look at :b)

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 15:41:23 GMT

btw Omar, my "xD" was a funny smile not really talking about the character 🙂 sorry but thanks again

Re: Labview + xbee read sensor, uncoding the hex string

Omar_II — Tue, 22 Apr 2014 15:58:57 GMT

Have you looked at regular expressions?

Re: Labview + xbee read sensor, uncoding the hex string

Raknugar — Tue, 22 Apr 2014 16:14:53 GMT

Thanks, i will try to implate this on my program 🙂

in a couple of days i think i'll manage to send you guys a feedback on this, once i get my hands on the rest of the material

you've been amazing with me

i wish i could pay you guys a beer or something

Re: Labview + xbee read sensor, uncoding the hex string

JohnCS — Tue, 22 Apr 2014 18:13:38 GMT

An XBEE API frame of type 0x90 represents a received RF packet from another device. In your packet, the first byte 0x7E is the start delimiter with which all XBEE API messages begin. The second and third bytes of the message you are receiving say the message is 0x13 (19 decimal) bytes long (not including the checksum). After stripping out one byte for the frame type (0x90) , 8 bytes for the 64 bit source address and 2 bytes for the 16 bit network address and 1 byte for the receive option, you left with a payload of:

32 322E 3639 0D0A

followed by a checksum of 0x85. The checksum is calculated as [0xFF - (sum of all bytes from API frame type through data payload)] and is equal to 0x85 for this packet.

In your message, the carriage return and the new line are actually part of the message you are sending from the remote device and not the end of message delimiter. I would guess that on the router end, you are ending the AT messages with a carriage return/new line.

API packets do not end with a new line/carriage return. The message length is given in the 2 bytes following the start delimiter (7E).

The safest way to make sure your message is complete and intact is to start reading from 0x7E, the next two bytes are the MSB and LSB of the message length. Read that many bytes plus one (the checksum). Then, verify the checksum before parsing the message.

In the case of frame type 0x90, the data payload always begins with the 15th byte. So you can discard the first 14 bytes and begin parsing there.

If you only have one remote device periodically sending data, I would consider changing your coordinator to the AT mode, then your messages will come in the clear and look exactly like the way they were sent. All ascii and no hex.

JohnCS