Modbus RS232 to RS485 converted 3

[techzone12]

I have a PLC that talks Modbus. I am going to use Modscan software running on my laptop (master), to pull data form the PLC (for initial testing purposes). The PLC have 3 terminal blocks for communications (+,- and shield).
In order for me to connect from my laptop comports (comm1, RJ485 to USB) to the PLC, I guess I will need a converter (RS232/RS485 or USB/RS485).
Since this setup is for testing only, I would like to buy a very basic converter. Can I make the converter myself?

Thanks

 

[danw2]

The converter is a tool that is needed to get the job done.

If productivity is your (or your employer's) goal, then buy the tool and get the job done.

If serial communications is your hobby, have at a design.

Dan

 

[dV8r]

I would start by trying it without the converter, attach both sets of TX -to- RX and the common. With short distances and 1:1 this often works for testing. The two hardware voltage specifications overlap slightly so with a two wire system the two look alike to the software.

 

[catserveng]

I use Modscan a lot for field troubleshooting, never have been able to use it without a convertor.

I use a little 9 pin to terminal strip type of convertor by B&B electronics, part number 485SD9TB, port powered and works very well, don't know if you could build one for the price they charge.

Regards,

 

[danw2]

I use that same B&B port powered converter, but I always carry a 12Vdc power wall wart power supply for it, because many laptops just won't provide sufficient power to run it.

Some port powered converters have no provision (no terminals) for external power. My opinion: avoid those at all costs.

I've never tried to connect 23 to 485 without a converter. Maybe I'll give that a shot sometime on a benchtop.

Dan