arduinoserialusb
I have two measurement circuitry connected to two separate Arduinos.
I need to grab and record data from the two simultaneously, so how can I monitor and record data from two serial stream from separate USB cords?
I don´t have a unix system but I have been using Cygwin so far. I´m currently installing Ubuntu on VMVirtualBox. Can I just open multiple shells in Ubuntu and record the data in that way given that I know my COM ports?
I2C is a bi-directional data bus. You appear to be using a uni-directional level translator (likely http://www.sparkfun.com/products/8745) wired such that it can only pass data from the low voltage side to the high voltage one, and not the reverse. This will prevent you from sending commands to the Accelerometer to request data, so you would only see anything if it decided to produce data on its own. (EDIT: apparently the convert is at least somewhat bi-directional)
Further, you must tie the VIO high. By leaving it floating you are probably letting noise trigger the chip somehow to occasionally produce data.
Also note that I2C requires pullup resistors.
Switching to SPI might be an option as in that case each pin would be un-directional, however you need to drive 3 outputs from the 5v to 3.3v side (/CS, SCK, MOSI) and your existing translator only supports 2. You could build something for the third from discretes.
If you left CS and SDO unconnected you might be able to operate the chip in stand alone mode where it would reliably produce data by itself, but then you would have to make the program capable of catching the data whenever it appears, perhaps by using an interrupt (or a polling loop if you can guarantee nothing else is going on).
Here is a tutorial on modifying the Arduino itself to run on 3.3v, thus eliminating the level conversion problem: http://www.adafruit.com/blog/2011/04/19/tutorial-tuesday-converting-an-arduino-to-3-3v/
Here is how I would suggest going about debugging this problem:-
Check the connections.. if you've mixed up signal ground and chassis ground (shield) you could get funny behavior just like you describe. Pin 7 on the DB-25 is the one you want to connect to DE-9 pin 5. I'll assume you're using a commercial adapter/cable or have one wired like this.
Maybe check the transmit out line to ensure it's idling at -12 ( < -3 anyway).
Make sure the instrument is set to RS-232, and not current loop (Jumper 7,8 and 1,2).
Try the most common serial port setting (9600/8-N-1), 9600 baud, NO parity, 1 stop bit switch 1, 2, 3 OFF switch 4, 5 ON switch 6 ON switch 7, 8 ON
Make SURE you understand which is 'OFF' and which is 'ON'. Don't laugh, I've seen this happen more than once, and some types of DIP switches are kind of ambiguously marked. If in doubt, an ohmmeter across the switch.. in fact you could check all of the switches to ensure they're working.
I like Realterm as a terminal program. It's free, and easy to change the parameters. Try it on something known working first of course, and look for an online tutorial. Really worth it.
If still gibberish after that, get a scope screen cap or photo and post it.
If you have a continuing need for a logic analyzer, this one is very cheap and relatively useful. Not as good as my Tektronix boat anchor, but this one will fit in a coat pocket. But I'd get a scope first if you don't have one. Even the worst scope is better than nothing.
Best Answer
It should work, but there is no need to install Linux just for this purpose...
You could do what I did: I opened putty windows, and set it to log the output to file. I made the serial output of the Arduino code so that it was pasteable (is that a word?) into Excel to be able to easily display the result as a chart.
It worked like a charm.