Some code to expore interesting old Human Interface Devices from before the era of USB. They all have serial (RS-232) connections and some of them are powered that way too.
Many early PC mice were connected via RS-232. Most had two or three buttons, but there was the Prohance Power Mouse 50 that had 14 buttons, and the Prohance Power Mouse 100 with a total of 40 buttons. Trackballs were interfaced that way as well. I have an A4 Tech WT-7P serial trackball that can operate in either "PC" 3-button or "MS" 2-button modes. I've also recently acquired a Microsoft Easyball and a Truedox 300 trackball.
Some force-feedback joysticks were connected via serial because the original PC game port was input-only (analog pots and buttons). The force-feedback motors need much more power than RS-232 can supply, so these devices have external power supplies. Some joysticks were serial, such as the Logitech Wingman Force Feedback, whereas the Microsoft Sidewinder Force Feedback used the MIDI port included in later versions of the PC game port.
Not something that is commonly seen as a HID, but it surely is one: the display. How about the customer display or pole display of a cash register, till, or Point-Of-Sale computer? I have the Wincor-Nixdorf BA63 customer display, a two-line by 20-character Vacuum Fluorescent Display (VFD). Other displays are bigger (e.g. the 4-line BA66) and/or use other display technologies (e.g. LCD). The BA63 is powered by 12V supplied through the same cable as the RS-232 serial interface.
The Spaceball was originally a serial device for use with very expensive 3D graphics workstations, so it had an RS-232 interface. The device was badged by several manufacturers, including HP, Logitech and IBM. The Spaceball 4000 FLX was serial, whereas the 5000 is a USB device. Older models like the Logitech Magellan were also serial.
A real rarity, the dialbox was an early computer graphics input device consisting of a row of pots in a box. IBM had one that used a serial interface (IBM 6094-010), also branded by Sun (370-1223-01) and SGI (9980992) Possibly all these were variants of the Danaher DLS80-1022.
Along with the dialbox, another example of a specialised interface device is the button-box. It usually had lights as well as buttons or keys. The classic example is the IBM Lighted Program Function Keyboard (LPFK), model 6094-020. That Prohance Power Mouse 100 could probably be regarded as a button-box with a built-in mouse.
The button-box may have had keyboard-like keys, but it wasn't laid out like a keyboard and wasn't intended for typing text. Many workstation keyboards had serial interfaces, but the standard IBM PC keyboard did not. It wouldn't make sense to offer an add-on full keyboard that had a serial interface. However, several vendors supply add-on numeric keypads for laptops. I have one which has a serial interface, the Genovation 623A.
Many early graphics tablets (or digitising tablets) were serial, but companies continued to make them into the early 2000s for people who didn't yet have USB on their computers. But the big advantage of USB was that it supplies power, and did away with the need for a special 9-pin connector with a power connector on the back. Can we find the serial protocols for these old tablets? I have a Wacom GD-1212-R, where '1212' represents the size (12 inches square) and 'R' means RS-232.
Not sure if this is really a user-interface device or not, but before we had USB, we had swipe card readers with serial interfaces (and PS/2 as well). What protocol and commands do they use?
We can buy USB-interface flight control yokes and throttle quadrants. Were these gadgets ever made for serial? What about car-style steering wheels and pedals, which are common game console controllers?
What other weird HID gadgets were made for RS-232?