You are right. Under the original plan it would have made sense to use some kind of PS/2 keyboard or have an MCU on the board. The customer has now decided that he's willing to lug around his laptop on-site after all and just use the serial port. So the immediate need has passed.

But I was left thinking that with the decreasing availability of serial ports on laptops and computers it is going to be harder and harder to use that option in the future.

Are there any portable "dumb terminals" out there at a reasonable price? Simply a keyboard and some kind of display with an RS232 port? Or maybe an I2C port? Or an SPI port? Or maybe all of the above? If not, I'm thinking one needs to be built and made available. It might not be a huge market but it seems that as fewer and fewer computers have serial ports that there will be more and more need for a way to easily access these kinds of devices that use serial communications for simplicity and cost.

Regards,
Craig Steiner