Hi Jameson,
I have trouble getting an RS485 connection to talk to one Omnimeter V3 (SN 10000063) using the Dash software.
I've built my own usb to RS485 adapter with the following parts from Sparkfun.com:
BOB-00718 (FT232RL breakout board)
BOB-10124 (RS485 breakout board) using a SP3481 chip.
These two boards were connected together as follows:
3.3V from FT232RL board to 3-5Vinput on RS485 board
TX-O from FT232RL board to RX-I on rs485 board
RX-I from FT232RL board to TX-O on rs485 board
TXDEN from FT232RL board to RTS input on RS485 board.
GND from FT232RL board to GND on rs485 board
This setup was tested with Hyperterminal, and a scope connected at A - B - GND (RS485 output) and i see data frames when typing on the keyboard. Also used your Dash software and try DISCOVER under the ADVANCED TAB, i see a bunch of frames being sent out on the scope ( A-B-GND output).
The voltage swings between (+3.3V and -3.3Vdc) when i connect the scope between the A-B RS485 line. Because the RS485 board operates at 3.3Vdc. Is this OK? You sell USB to RS485 adapters, are they setup in a special way that would explain why i am not able to talk to my Omnimeter V3 ?
The casing of the Omnimeter V3 tells me to connect to 20-21-22 (writing on the case) is this OK? I cannot find any writing documentation on your site that tell me that RS485 is on pins 20-21-22 for V3 Omnimeters.
Is there any way of confirming this by reading voltages of those pins (or using a scope to see pattern string coming out of the A-B RS485 lines?) What DC voltage should i read between A and GND, B and GND , A and B on the Omnimeter V3 RS485 pins?
Cheers Jameson,
Jean-Francois
I haven't made RS-485 communications work
-
noisette123
- Posts: 4
- Joined: Sun Aug 26, 2012 7:53 am
Re: I haven't made RS-485 communications work
Hello Jean-Francois,
I am really not able to comment with any kind of authority on other kinds of RS485 converters. We have tried dozens of different converters and many of them simply do not work.
I would imagine that the FTDI chip you had would work, but do not know about the configuration of the RS485 transceiver board. You can start playing with biasing resistors and terminating resistors, but other than this I will not be of much help.
I would really recommend our USB to RS485 converter (not to sell you, but because it works so well): http://www.ekmmetering.com/ekm-metering ... erter.html
From the Serial number you gave, it looks like you are using the Omnimeter II UL v.3. This is our UL Listed Omnimeter. The RS-485 connections on this meter are RS-485 A+ is port 20, RS-485 B- is port 21.
The best way to "see" your RS-485 output (rather than using a scope) is to use a serial sniffing software such as "Advanced Serial Port Monitor". You will be able to see if you have good clean data or if your data is garbled (usually because of bad terminating or biasing resistor values).
Hope this helps.
I am really not able to comment with any kind of authority on other kinds of RS485 converters. We have tried dozens of different converters and many of them simply do not work.
I would imagine that the FTDI chip you had would work, but do not know about the configuration of the RS485 transceiver board. You can start playing with biasing resistors and terminating resistors, but other than this I will not be of much help.
I would really recommend our USB to RS485 converter (not to sell you, but because it works so well): http://www.ekmmetering.com/ekm-metering ... erter.html
From the Serial number you gave, it looks like you are using the Omnimeter II UL v.3. This is our UL Listed Omnimeter. The RS-485 connections on this meter are RS-485 A+ is port 20, RS-485 B- is port 21.
The best way to "see" your RS-485 output (rather than using a scope) is to use a serial sniffing software such as "Advanced Serial Port Monitor". You will be able to see if you have good clean data or if your data is garbled (usually because of bad terminating or biasing resistor values).
Hope this helps.