Using a laptop USB port to connect to a RS-232 serial device.

Thread Starter

Walks91

Joined Apr 28, 2018
20
I'm trying to connect a virtual serial device from my laptop to a RS-232 > Ethernet/IP converter (EIP-2202). I'm only using a virtual serial port to get an idea of how my converter sends and receives data. I know this can generally be solved with a simple USB to RS-232 converter. However my converter needs to be individually wired, there is no connector. My serial device only has wire connections for CTS, RXD, RTS, TXD, 24vdc power, common and chassis ground. I have a 24v power supply to use for the converter.

I was thinking about using a USB > RS232 cable and cutting the serial connector off and then determine which wires are which. When I know which wires are the the ones I need, could I just hook the four of them up? I looked at some USB > RS-232 converters and there is definitely some circuitry involved so I want to make sure this would actually work before I go cutting up my cables.

An overview of my project is to create a virtual com port on my laptop, connect laptop USB to the converter's serial port > connect the converter back to my laptop via Ethernet/IP. The converter is a Comtrl EIP-2202 and has it's own IP address. If ip addressing conflict might be a problem I can maybe use a VM with a different ip to create the virtual com port.

Thanks for any help!
 

Yaakov

Joined Jan 27, 2019
1,612
It's hard to understand just what you are trying to do, but, an ordinary USB serial port adapter will have a DB9 connector on it. You can get a mating DB9 and wire it to the screw terminals on the EIP-2202. That would be the easiest and most sensible way to do it, so far as I can understand your goal.
 

Thread Starter

Walks91

Joined Apr 28, 2018
20
I want to take a USB > DB9 cable like in the picture shown, cut off the DB9 connector and connect the individual CTS, RXD, RTS, TXD wires to my converter. So it would be a straight cable from the USB port on my laptop to the serial connection on my converter. Does the DB9 connector part of the cable contain circuitry for the conversion?

I agree with you that using the port adapter would be easiest, I'm just trying to use what I have at home.
upload_2019-2-21_16-30-8.png
 

Yaakov

Joined Jan 27, 2019
1,612
I want to take a USB > DB9 cable like in the picture shown, cut off the DB9 connector and connect the individual CTS, RXD, RTS, TXD wires to my converter. So it would be a straight cable from the USB port on my laptop to the serial connection on my converter. Does the DB9 connector part of the cable contain circuitry for the conversion?

I agree with you that using the port adapter would be easiest, I'm just trying to use what I have at home.
View attachment 170697
Yes, in the case of the device you show, that connector has the active electronics molded in. you need the signals on the pins of the DB9, not the ones on the wires from the USB.
 

Thread Starter

Walks91

Joined Apr 28, 2018
20
I posted this in the other thread so I might as well post it here. My temporary solution is to daisy chain my USB > RS232 cable to a normal RS232>RS232 cable. It should hopefully work until I get one of those smaller USB > Serial converters delivered.

Thank you for the help!

upload_2019-2-21_17-31-7.png
 
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