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Weird serial communication problem ...

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LAN_403

lpfthings

Sun Jun 27 2010, 02:53PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

I bought a Silicon Chip Web server in a box kit today, and put it together. It has a RS232 output, on a 3 pin header: RX, GND, TX

I connected GND to Arduino GND, TX to Arduino RX, and RX to Arduino TX.

The web GUI for it has the option to send strings, strings with newline, and decimal character code.

I have setup the Arduino to just echo back anything it recieves:

void setup() {
 Â Serial.begin(115200);
}
void loop() {
 Â if (Serial.available() > 0) {
 Â Serial.println(Serial.read());
 Â }
}

Baudrates on both sides seem fine.

Here is the problem:

Whatever I send, seems to get translated into a bunch of numbers. If I send 1 thru to 10 thru the decimal character code option, it gives me:

Sending it 1 - 10 thru string with newline:

abcd with string and newline:

If I send string without newline, I only get single values.

1 to 13:

a - z without newline:

A - Z (Caps) without newline:

The numbers seem consistent. Like, if I keep sending it the same value, it keeps giving me the same value, I just don't know what the values mean ... and how they are encoded, really strange!

Cheers,
Dan :)

Bjørn

Sun Jun 27 2010, 03:14PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

If your signal is inverted then the result would be something like what you get so look into that. Have a look here too:

lpfthings

Sun Jun 27 2010, 03:23PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Thanks Bjorn, seems like it could be my problem :)

Since the ATMega328 already has direct RS232 input (SInce they use a FTDI chip to generate it), is there any way to invert this signal without having to use another IC?

I'm sorry if this seems ignorant, I really do not understand serial well

Heh nevermind, I'll just pick one of these up today:

Cheers,
Dan

klugesmith

Mon Jun 28 2010, 05:36PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Hi Dan.
Since your data are repeatable, I'm sure you can resolve your problem by studying the reported 1's and 0's with respect to an ASCII character table, and looking for the pattern.

Things to pay attention to:
1) Voltage levels.
1A) RS-232 is a bipolar standard, where "Mark" voltage (data=1 or idle line) is negative, commonly about -10 volts, and "Space" voltage (data=0) is positive, commonly +10V.
1B) "RS-232 compatible" serial Tx and Rx on microcontrollers, or the logic side of level-translator chips, have TTL voltage levels and the opposite polarity. Mark voltage (idle line or data=1) is > 2 V; Space is < 0.8 V.

2) Parity and stop bit options -- there's no standard, but transmitter and receiver must have the same settings.

3) Bit order: LSB is sent first, right after the Start bit which is the first logic 0 (Space) voltage.

As a baby step, try a loopback configuration with Arduino Tx and Rx pins tied together. Then anything you send to the Tx should appear at the Rx. You might also start with a lower baud setting, like 9600.

...

Mon Jul 05 2010, 12:21AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I am confused as to exactly what you are doing. Keep in mind the arduino TX and RX pins are internally connected to the ftdi usb-serial chip, and any data that appears on the terminal inside the arduino software is present on these pins. Generally when connecting external serial peripherals you will want to use the SoftwareSerial library to create a serial port on 2 unused GPIO pins. My understanding is that it is possible to use these pins to connect to other stuff, but you have to 'fight against' the usb-serial converter so it is not recommended and may be what is causing your problem.

I would recommend starting by connecting the webserver's tx/rx pins together, and making sure that the web interface behaves as you expect it to. After that is working, connect the tx/rx pins to the new software serial port on the arduino, and have it echo received characters from the web server out the arduino debug port (the normal serial.println interface you are using now) and watching what comes out in the terminal in the arduino software. After that is working correctly, then try and send characters from the computer to the arduino, etc.

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