I'm working with a group to design a ventilator for low cost, rapid deploym ent... or something. There is presently a decision being made about variou s methods of detecting end of travel for the back stroke of the motor. One of the selection criteria is "simplicity", rated 1 to 3. I don't see that as an objective value, rather a subjective rating of what they think of ea ch approach. Cost is rated from 1 to 3 without any real consideration of a dollar (or pound since this is a UK project) figure. The three methods th at use a detector each are rated 1 on cost (because there is some) and two methods are rated 3 on cost because they use timing (guessing) or motor cur rent on reaching a mechanical stop.
So do Hall effect sensors have any real issues such as magnetic interferenc e? They work off of a magnetic field, but not a rapidly varying field (the motor output is single digit RPM in use) so will local magnetic effects im pact it, like the motor current (brushed DC)? The sensor will probably be9 inches away. Is a magnet built into Hall effect sensors or is that requi red to be added?
Another choice is an optical sensor. They list as a disadvantage optical i nterference! That seems rather unlikely in a closed box especially. There are openings, but not large. For some reason this one is listed as poores t in simplicity. Seems simple to me and reliable.
They list circuit boards as being needed for those two and a micro switch. I know these can be mounted on cables, but is there a reason why that woul d be a bad idea for reliability? I recall in my very early days in enginee ring seeing front panels with switches and LEDs being wired up by hand via ribbon cable and heat shrink tubing. That was equipment for a NASA ground station, forty years ago. Likely they would not accept that now?
There is also the option of the motor shaft encoder, but that is significan tly more expensive and I recall there was a strong dislike of the $15 price . I suggested they include a couple of the options in the circuit board an d after development is done leave out the one you don't use. They seem to think they can make all the decisions without knowing for sure how this wil l need to be used really.