This is for the die hard DIYers out there...
I have made several serial port pedals. Increasingly, however, transcribers can't use them because their computers don't have a serial port. I have had hit-and-miss luck with USB-to-serial port adapters...but even when they hit, they generally take some tweaking.
I may be wrong, not having purchased a USB pedal, but most of the commercial pedals seem to have drivers that need installing. This board is full of problems with the various pedals and drivers.
So I kept looking for a better solution, and eventually stumbled on this YouTube video:
I took Matt Richardson's (the guy in the video) approach a little further to make a four button pedal. The pedal I made has, from left to right, REWIND/STOP/PLAY/FAST-FORWARD. This is accomplished by "re-purposing" the keyboard controller so that the buttons on the pedal activate F7/F4/F9/F8. In other words the foot pedal is essentially a keyboard with just four keys--those four function keys.
The lovely thing about this approach is that it will work with any computer that has a USB port. There are no special drivers needed, since as far as the computer knows, the foot pedal is a keyboard.
I used the same model keyboard that Mr. Richardson used, and have mapped a schematic for re-purposing it:
Dell L-100 keyboard to foot pedal schematic
I think a similar "hack" should work with other keyboards, but you'll need to map where the contacts go since it will be a bit different for every keyboard model.
I appreciate the help I have gotten here! Hope this helps someone else.