Active3 years ago
- I am trying to take a comma separated (and null terminated i think) string sent to an arduino via the USB serial interface and then output it via an attached LCD. The LCD part works fine but i can't figure out how i would parse a comma delimited string and extract the individual values on an arduino.
- Serial.parseFloat returns the first valid floating point number from the Serial buffer.parseFloat is terminated by the first character that is not a floating point number. The function terminates if it times out (see Serial.setTimeout).
A simple example of receiving data from the Arduino. Arduino to Visual Basic 2013 Communication. The example uses a very simply form and shows what ever it recieves from the Arduino in a text box. The Arduino Sketch. The Arduino Sketch sends the string “1234” over the serial connection once every second.
I'm writing an app to control my robot with my Android phone over Bluetooth, everything is goes well, data is echoed and verified, but I'm having some trouble with the protocol, specifically I want my robot's wheels to turn when I send a command such as
s,10,100
or s,-30,-10
.. (values in percent).My problem is that when I want to parse my wheel speed command on my Arduino I must parse from up to 4 separate
bytes
to int
, for example s,-100,-100
makes my robot go backwards at full speed, but how do I parse this so I can call setSpeed(left, right);
with left
and right
equal to -100?I know I can separately analyse every byte and put them together to get an integer, but it's not very elegant and there's probably a better solution to all this already, unfortunately I haven't found it yet.
Here's my Arduino function for parsing my commands:
You call it this way when parsing something like
s,100,-100
(must be 0
terminated):Solenoid
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2 Answers
Just read character by character into a state machine. It's simple and efficient.
To read in a number digit by digit, do this: Start with zero. For each digit, multiply the number by ten and add the value of the digit. So, for example, reading 97 would work like this:
- You read in a digit with no prior digit, you start with 0.
- You read in 9 and compute (0*10)+9 -> 9
- You read in 7 and compute (9*10)+7 -> 97
- You read in a non-digit, you output the 97.
Here's a fuller example
s,10,100
:- You start in the 'ready to read command state'.
- You read 's', 's' is the command. You switch to the 'ready to read first comma' state.
- You read the first comma, you switch to the 'ready to figure out the sign of the first parameter' state.
- You read a digit. Since this wasn't a '-', the first parameter is positive. You set the first number to the value of the digit, 1. You are now in 'reading first number' state.
- You read a digit, 0. You set the first number to 1*10+0 -> 10. You are still in 'reading first number' state.
- You read a comma. You are now in the 'ready to figure out sign of the second parameter' state.
- You read 1. The second number is positive (since this wasn't a '-'). You set the second number to 1. You are in the 'reading second number' state.
- You read 0. The second number is now set to 1x10+0 -> 10. You are still in 'reading second number' state.
- You read 0. The second number is now set to 10x10+0 -> 100. You are still in 'reading second number' state.
- You read an end of line. You execute your results: The command is 's', the first number is positive, the first number is 10, the second number is positive, the second number is 100.
- You switch back to 'ready to read command' state.
![Arduino serial input example Arduino serial input example](/uploads/1/2/4/8/124802142/119238318.png)
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I like the answer by David Swartz, but thought I'd play devil's advocate.
Reading the data in as binary can be elegant, it just depends on what you need to do with it.
In the following example, data is read from serial until it sees the binary delimiter
0X7F
. The bytes read are stored in the inData
char array. Take a look at the documentation for Serial.readBytesUntil()
This byte can then be cast to an integer or otherwise manipulated. Keep in mind the maximum value for this would be +/-126 because this is a signed char (127 is a delimiter and wouldn't be seen as a value).
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You could access these values by with something like the following:
I tested this out with the following bash command (after making sure serial speeds were set properly):
Some rough sample code that I wrote can be found Here
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Active3 years, 3 months ago
I'm currently working on an arduino project at University. Basically what I am trying to do is send a string of data from VVVV to arduino, however I need to parse the data into an array and I have absolutely no idea how to do this!
The string being sent from VVVV is something like this; U,c,R,|,W,H,P and I need each of those values to be written to a specific servo each time, so value 1 need to go to servo 1, and so on.
Here is my code at the moment, I realize its coded pretty badly, and I do intend to make to make it more efficient when I have worked out how to parse the data.
Edit - I should probably mention that I'm eventually looking to use 7 servos, but for the moment I'm just using 4 in my circuit. Also, when I upload this patch and enable VVVV, the arduino just disconnects.
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3 Answers
@opc0de This serial issue has cause a lot of confusion. Including to myself. Possibly similar issue here.
I recently dabbled into this. The Arduino automatically resets when it receives serial communication from most things other than the Arduino IDE. This is why you can send from the IDE but not node.js.
I have an Uno and put a capacitor between Reset and Ground.Here's a page with some good info on the subject. Good luck. http://arduino.cc/playground/Main/DisablingAutoResetOnSerialConnection
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Bose
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If you want to assign the value as soon as received, you can do this:
If you want to have the received values stored on the array to do something more later, then:
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