I am trying to build a pull switch for my invention that can survive 10 million cycles, and in a previous question here I recieved advice not to use a mechanical contact.
The other problem is size. The sensor assembly cannot be larger than 1x1x4 centimeters and the sliding distance can't be larger than 2 centimeters, otherwise I would need to do a mayor redesign of my invention.
There won't be more than 3-4 switching cycles per second, usually less, and the 10 million cycles is my extreme worst case scenario after several years of use. The sensor assembly will be sealed so there shouldn't be any problems with moisture, but perhaps some loose material from the casing due to wear and tear.
I've searched the net for a suitable pullswitch but found nothing that would work.
My questions are:
I tried using a hall effect switch with a permanent magnet and it worked fine, but wouldn't magnetism cause problems with EMC testing, CE and FCC rules?
I need to use a non latching hall effect switch, are there any reliability issues with those?
Do permanent magnets loose some of their strength over time? The sliding distance needed to close the switch cannot change more than a few milimeters.
Are there any other good alternatives besides hall effect sensors? Perhaps some form of piezo sensor? Preferably one that can work with the voltage levels of Arduino, though I have plenty of room on my PCB for resistors so wrong voltage shouldn't be a showstopper.
Best Answer
Not if it is a tiny permanent magnet - fridge magnets are typically not FCC certified. A varying magnetic field is more of a concern.
Not if the Hall Effect switch is from a reputable manufacturer. Adding the identified switch(es) to the question will help provide additional insight.
Some types of permanent magnet lose field strength due to impacts, but a tiny rare earth magnet will probably outlast the rest of the device by orders of magnitude.
That would depend on the purpose and application of the switch, but capacitive sensing lends itself to really long operational life, with the actual switching by a MOSFET for instance.
There are many capacitive sensing products available, including some self-contained cap-sense pushbutton and proximity sensor (QTouch and QTouchADC) ICs from Atmel that do not even require a sensing electrode, the IC itself works as the sensor. See these two references: 1, 2.
Another option is light path interruption sensing, such as using an LED and a photodiode, or prepackaged such sensors with both parts integrated.