Testing an RS232 device

[Angus]

I have this RS232 device that isn't working, and I don't know if it is a hardware or software problem. Is there a 5‚¢ solution to testing the receive conductor for activity? I don't have an oscilloscope, but I do have a multimeter. Obviously, however, it is designed to expect AC signals to be no more than 60Hz, not 115200bps.
The device is an IR receiver, FWIW. I think all the energy it produces comes from the transducer, and doesn't cheat the hardware flow control lines out of power, like mice used to. It certainly doesn't have a battery and I don't plug it into the wall.

 

[blueroomelectronics]

Is it something you built yourself?

 

[Angus]

No, but I'm pretty sure it wasn't mass produced either. I just bought it from some guy.

 

[blueroomelectronics]

We'll need more than that.

 

[Sceadwian]

A DC or AC meter will pick up SOMETHING if the transmitter is putting out data.

 

[Angus]

We'll need more than that.

Like what?

 

[blueroomelectronics]

Model number would be a start?

 

[mneary]

The RS232 line is likely to be the source of power. The signal at an IR receiver isn't enough energy to supply RS232 which in today's terms is pretty power hungry. Good news is, they can steal a lot of power from a proper RS232.

First thing to check is, does the computer supply a proper RS232 voltage and current? TXD(3) should be a solid +V when idle, preferably 6V or more (spec is 3-12). They probably are stealing -V from RTS(7) or DTE(4). One or both of them should have -6V or better. If you don't get good readings on the open computer port, it's a wimpy RS232 with no power available to steal.

The RD line should be idle at +3 to 12 volts, and active at -3 to 12V. If you place an LED with anode to ground, and a diode and 2.2k resistor in series to RD, it should blink on any activity.