What should a pendant look like?

[JAZZCNC]

Most pendants don't want single handed operation because that makes it unsafe and very easy to crash by accidentally catching knobs buttons etc.

Step selection(course/fine) is critical with pendants and one of the single most used features. Blast across bed in Continous mode then switch to step and creep up on material. Having step resolution is important because you won't want to jog at full rapid when setting Z axis for instance but equally you won't want to jog in steps of 0.1mm while going down close to surface but when with in mm's of surface you will want to step into this 0.1mm or higher resolution.

For the electronics then I'd look into the POKEY's device if using mach3 as it gives loads of I/O which you'll need for a Pedant and it's designed with pendants in mind and makes it easy.
Arduino is the next thing I'd look at but again you'll need some way to let the control software know and lack of I/O with Parallel Port will be your enemy.!

So my minimum controls would be E-stop, Axis selection, Step selection, Step resolution, and axis jog buttons.
After this then things like spindle control or feed over ride, feed hold etc are things to consider.