I'm putting a new kit together and would like some feedback.

Maxim makes a MAX3160 IC $17 that has both an RS232 & RS485 selectable interface (also includes RS422 but I'm not going to offer that)
Seems like a pricy part as the kit will only offer one or the other when sold (user could pull the socketed part and swap in their own so...)
* I guess I'm answering my question as I type this So I'll pose another query.

Jumpers to select RS232 / 485 (slightly higher cost)
or simply only install the IC ST232 or SN75176 depending on your requirements.

I'll use a DE9 connector though, just like the MAX3160 schematic.

* Incase you missed it I'll avoid the MAX3160 as it would be the most expensive part in the kit!

 

I wonder if that's what's used on alot of commercial boards where 232 vs. 485 is selectable. I did lots of stuff with RS485 years ago. How far of a cable you going to connect between devices? Problem I often see with 485 circuits on commercial boards is that they don't take into account ground differences very well, don't offer or even mention termination resistance. Our current equipment at work goes from building to building and we optically isolate them.

 

This is true. I'll add bias & terminating resistors. I would guess commercial units use the MAX3160 but they tend to be very expensive.

 

I'm wondering why you'd even want to offer RS-232, as it's slow, legacy, and is disappearing from newer computers. I don't know what your application is.

You might want to look at offering USB 2.0 or 3.0 interface instead.

 

A USB host is beyond the scope of the project, I agree it's pretty old. RS232 still has a handful of useful devices (Modem, PC, RF extenders eg: XBee...) where as RS485 has multidrop and range but it's not common on PCs.

The bigger picture is it's an PIC 18F based Ethernet to I/O controller (JDS Stargate, ELK Magic, Sensaphone Web600)

The RS232 mode would be handy where Ethernet isn't available but phone connections are eg: Cottage.

 

If it would double the price of the kit, make it an optional upgrade.

If the price won't change enough to chase away customers, make it switchable.

 

As SgtWookie pointed out RS232 isn't used as much as it used to be so making it an extra cost option (a ST232 and four caps) keeps the price down. It's really easy to add the pads and traces on the PCB. My target projected MSRP is $150

 

How about IR.

Then you can sell RS-232 dongle, USB dongle, Parallel port dongle.. and they can still comunicate with the device.

That way any future ports can still be supported via dongle rather than new board.

It can double as an EVERYTHING to Ethernet adapter if needed.