I had a peak inside the switch / speed controller box on my scroll saw. It seems to be a NVR switch followed by a reasonably sophisticated electronic speed controller, with a two wire feed to the induction motor at the end of it (there is also a two wire connection to a 15uf high voltage cap that is housed in the same enclosure).
Now what would be nice, would be to add the capability to have a foot switch to stop / start the saw (momentary action - push to go, let go to stop kind of thing)
The NVR switch prevents the easy option of switching the mains in. So the options would seem to be:
1) Insert a switch between the NVR switch output and the mains into the speed controller.2) Switch between the output of the speed controller and the motor
3) Combination of 1 or 2 above in addition to a foot pedal containing a suitable variable resistance to take the place of the speed selection knob - giving a sewing machine like control over speed.1) seems like the obvious one, but can anyone thing of particular pros/cons of the options?
Next a suitable connector...
Can anyone suggest a suitable connector? I recall in the past there being a Telefunken style figure 8 socket that also integrated a switch that was actuated when the lead was inserted, but I can's find anything like that at the moment. It would be nice to have a smallish mains rated connector system that could be configured to leave the system running normally when the external switch is disconnected, but would automatically adapt to using it when plugged in. (and preferably with the female bit of the connector on the saw such that you can leave a pin live without risk!)