Serial board really RS-232 compatible?

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Dear Sirs,

I wanted to modify a home alarm and use an old Siemens (with his Sync Station which through a serial port communicates with a PC for the normal people) to send SMS.

I found the MaxSerial board perfect for attaching the output to the cable of the Sync Station but I don't know why it doesn't work.

I have uploaded the code and the board works perfectly and in the 'serial monitor' appears the commands that the board sends. The telephone attached to the serial port of a PC works, you send the commands using an hyperterminal and it sends the SMS, so the problem is not the Siemens terminal.

The problem comes when I attach the board to the telephone, I think it comes because the different voltages. To trace the code I have put different blinking of the control led and when the board is attached to the telephone the first blink of a serie has a shorter duration. The MAX232 compatible chip afirms to say it is RS-232 compatible but until now not for me :frowning:

Can anyone tell me something about this?

Thanks in advance and regards.

2

I suspect an issue with TX and RX lines being crossed. Your device and the MaxSerial apparently both have female DB9 connectors, is this correct? If so, you probably need a null modem cable that crosses pins 2 and three (with pin 5 straight through) to get them to talk.

-j

3

Thank you very much for your information. With the null modem configuration I see that the communication works (for example changing the CMC number for sending the SMS).

Now my problem deals with the programming part but at least the hardware see it works.

Thank you very much again!