Monoprice rs232 over cat 5


Active Member
Hey guys I am trying to interconnect my two HAI Omnipros with a Cat 5 cable utilizing the RS232 extender from Monopric found here:

I can't seem to get it to work. I confirmed the cable tested properly. The kink is that I need to make db9 to rj45 connections for the omnipros. I replicated their design (I believe properly) from their kit that is used to control the russound and other serial devices. The one other issue is that I am using TWO of their reverse order cables (phone style literally reverse order on one side). So I believe I am undoing that RX to TX when using two of them. So I reversed pins on my DB9 to RJ45 connector and tried it but alas it does not work. I have tried about 20 different combinations of DB9 to RJ45 configurations thinking this was my problem but I have no idea. I believe my programming is proper. I see the one unit blink on its transmit light when I send the command but that is all I get.

So I don't know if the Rs232 unit is on or works (there are no lights indicating anything) and one reviewer on their site mentioned he had to short points 6 and 7 so he could get a proper handshake. I don't know if that was the extender or device specific. Not knowing what to do I tried it but still not any better.

Any suggestions or troubleshooting ideas would be GREATLY appreciated!


How long is the extension cable?

The best way to do this is to use a multimeter to establish the pinout of the working cable, then use that to check your end to end home made cable. You can use a side of a resistor to get to the female pins if needed when doing this. If you need help with this let us know.
The cable is probably 500 feet - and that is probably an over estimation. I ordered two of the kits for serial connecting but I am 99% sure I have it correct....

Does me theory of using two round over cables canceling each other out make sense?

The device is rated for something like 1000 meters or something crazy. I'm using the device to extend not using a straight cable
Do those units map TX to RX and RX to TX? If not, you may need to take that into account with the cables you use.
I got it working today! Here is my summation:

I used one of an HAI db9 to rj12 adapter that is supplied for controlling serial devices (which we referenced above) on one end and made a copy on the other since I didn't have another handy. I tried the resistor lead as a probe but it didn't work. I made a cable with a RJ12 end on it and just stripped the wire bare and tested that way. The older I get the worse my vision and I just couldn't get an accurate read.

I didn't have to flip the RX and TX on the other side apparently the rs232 adapter will make the switch in hardware.

For your information (if you care or it comes up again and for my notes) the pin out's / color coding for a standard DB9 to RJ45 adapter are:

The numbers below are the DB9 side and the colors are a standard DB9 to RJ45 pin configuration

7 Not Used
8 Not Used
9 Not Used

BLUE and WHITE aren't used in this situation.