Author Topic: USB to serial converter termination  (Read 727 times)

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Offline drummerdimitriTopic starter

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USB to serial converter termination
« on: June 15, 2020, 03:11:24 pm »
I just received this USB to Serial converter cable: https://www.aliexpress.com/item/4000570382636.html?spm=a2g0s.12269583.0.0.390f2b8bk7eW2b  which is plug and play so

windows automatically downloads the driver for it but when I try to plug it into my Meanwell TN-1500 inverter via a RJ11 connection and make sure the hardware and software are using the same COM port and BAUD rate, I get a "Inverter not found" error message.

I cut the end off the cable thinking the original cables pin configuration may be wrong for my inverter and there are three conductors inside (black white and green) but since I don't have the pin-out, I cannot follow the manual (see attached manual, page 3) to crimp a new RJ11 connector with the correct wire arrangement.

Does anyone have a clue what conductors correspond to the correct pins from 1-6 on an RJ11?

 

Offline MarkF

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Re: USB to serial converter termination
« Reply #1 on: June 15, 2020, 04:07:29 pm »
Paragraph #2 in your linked document gives you the pinout.
You may need to swap TXD and RXD?

With a meter you can find what color is ground and guess at the other two colors.



« Last Edit: June 15, 2020, 04:09:44 pm by MarkF »
 

Offline Ian.M

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Re: USB to serial converter termination
« Reply #2 on: June 15, 2020, 04:20:46 pm »
Diagram A in the manual you attached shows the relationship between the RJ11 pinout and the standard DE-9 PC COM port pinout. 

To identify the wires:
The ground wire should have continuity back to ground on the USB connector, and if you plug the cable into a PC and open the port in a terminal program, with no data being sent, one of the remaining wires will be a floating input (RxD) which will measure close to 0V and the other (TxD) will output a voltage: +5v or +3.3V if its a logic level (aka: 'TTL') USB serial adapter, and negative -5V to -25V (but unlikely to be more than -9V) for a true RS-232 levels USB serial adapter.  See  http://tldp.org/HOWTO/Serial-HOWTO-19.html

The two types of adapter aren't compatible, your inverter expects true RS-232 levels and, as its only got three wires, almost certainly doesn't provide USB Vbus so you cant use a MAX3232 serial level converter chip, so if you measure a positive voltage with the port open, you'll need to get a different adapter (preferably one with a DE-9 plug as they almost invariably use RS-232 levels).
« Last Edit: June 15, 2020, 04:22:34 pm by Ian.M »
 


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