Two-wire serial interfacing land-line modem issue

Projects Networking, Protocols, and Devices
1

Greetings to all as my first post.

I`m trying to control an Acorp 56EMS modem with Arduino Uno via serial comm.
Successfully tested all needed AT commands with two-wire serial PC->Modem connection, but when using the Arduino in A->PC and A->Modem configuration the following happens:

A->PC two wire serial : Correctly showing Serial.printed text at the IDE Serial Monitor, but received scrambled at PCs serial port (equal baud).
A->Modem two wire serial : Even just wiring to the modem, runs both modem status LEDs (TX/RX) continuously. (no signs of transmission)

Any suggestions will be in use.

Thanks !

2

Show us the code you use and the wiring as well as a link to the modems user manual/datasheet.

Correctly showing Serial.printed text at the IDE Serial Monitor, but received scrambled at PCs serial port (equal baud).

So you have two serial interfaces? The UNO has just one...

3

pylon:
Show us the code you use and the wiring as well as a link to the modems user manual/datasheet.

Wiring: Arduino Pin1(TX) -> Modem DB25 Pin2(RX) with GND to DB25 Pin7
No manual concerning serial details is available.
About the code, even the simplest try just with serial.begin, delay and serial.print sends corrupted data to the pc.

So you have two serial interfaces? The UNO has just one...

That was an attempt to debug with SoftwareSerial lib

Ive found that despite rs232 specs ("Valid signals are plus or minus 3 to 15 volts") there may be an issue with the lower voltage from arduino (~4.9v) compared to the PCs port (~11v)
Will try to use MAX232 interface chip in Monday because its non working day now where i live.

4

Problem solved by using MAX232 chip for equalizing voltage levels.
10x Pylon.