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Arduino RS-232 to RS-485 Converter [message #3033] Mon, 28 April 2014 22:51
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If you have one of these RS-232 to RS-485 converters (probably bought from E-BAY):
 Arduino rs-485 to rs-232 Converter

You will probably get a description like this:

* It is able to convert RS-232 signal to RS-485 balanced differential signal and extend the communihoneyion distance to 1.2km.
* It uses a particular pump to gain power from RS-232 signal (RTS, DTR, TXD) without initializing the RS-232 series interface.
* This interface converter does this without requiring any AC or DC power.

You will have problems with this converter from the arduino unless you read the spec sheet. Unfortunately the sellers will probably not give you the schematic or tell you how the circuit works.

I used this converter along with an arduino using the TX and RX TTL output to a MAX232 circuit, then this plugged directly into the RS-232 to RS-485 converter which in turn was connected to the power meter.

The response from the arduino was perfect. Not problems. But the power meter was not receiving the correct data.

The problem that the sellers don't tell you very clearly is what is needed to power the converter.

The trick here is to read this sentence a few times to understand it: "It uses a particular pump to gain power from RS-232 signal (RTS, DTR, TXD) without initializing the RS-232 series interface." So in order to get this RS-232 to RS-485 converter to work, you will need to hook the RS-232 serial port's DTR and RTS pins to the 5V Pin on the arduino (or another source if you have it), pin 5 of the serial port to Ground on Arduino, and the TX and RX from the Arduino to the corresponding pins 2 and 3 on the RS-232 port.

Pin 4 (DTR) - Jumper these two pins and hook to 5V from arduino
Pin 7 (RTS)

Once this is done, the RS-485 device will have enough power to send the correct data through.

*You could get around all of this by just purchasing a RS-485 plug in module for the arduino. It will save you a lot of time since these modules will convert the data for you without having to go to a TTL to RS-232 conversion, then to RS-485.
 Arduino rs-485 Converter Module

[Updated on: Tue, 13 May 2014 02:16]

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