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Debugging a unknown RS232

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soeren72:
I have a pelletburner with a DB9 connector on the back,  (normally used to connect a GSM module for remotecontrol)
Any ideas how to go about, finding out how to control it.

I have no information in serial setup (speed and so on)
And I don't have the GSM modul

any help would be nice

br Soeren

DrGeoff:
Hook up a scope to the TXD line and switch it on. It may send out a stream of characters to indicate that it is ready. Examine the timing of a character and calculate the baud rate (and start/stop/parity settings).
If you don't know what the protocol is then it may be difficult, however if it was supposed to talk to a GPS unit it may be 2400 Baud NEMA protocol.

soeren72:
Thanks for replying,
It is a GSM not GPS

I tryed to hook up a pc, with a terminal program at different serial settings, and once there was a lot of ascii
but I havn't been able to recreate it again

scrat:

--- Quote from: DrGeoff on September 22, 2010, 11:58:12 am ---Hook up a scope to the TXD line and switch it on. It may send out a stream of characters to indicate that it is ready. Examine the timing of a character and calculate the baud rate (and start/stop/parity settings).
If you don't know what the protocol is then it may be difficult, however if it was supposed to talk to a GPS unit it may be 2400 Baud NEMA protocol.


--- End quote ---

Using a PC serial port may take a lot of time, if you don't know baud rate and so on.
If you haven't by hand any oscilloscope, then you can use your PC's soundcard, just to start.
A large capacitor in series with a resistor and a couple of antiparallelled diodes will make the signal to stay into an acceptable range for the line in of a soundcard. There are a lot of "soundcard oscilloscopes", choose one which allows to set trigger. The only problem would be if a high baudrate is selected, but I think it is not so probable.

jimmc:
A very useful program for debugging RS232 protocols is 'comDebug' from http://www.windmill.co.uk/serial.html
Free but requires registration.

For an 'all singing all dancing' soundcard oscilloscope try 'Visual Analyser' from http://www.sillanumsoft.org/
Free. Includes oscilloscope, spectrum analyser,LCR meter (requires simple external circuit), counter, AC voltmeter, waveform generator and more!

Jim

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