Can I still join the tactile switch slapfight? It's really simple, switches are rated for a maximum voltage, and then a maximum amperage at that voltage. Run at a lower voltage, and you can use higher amperage, because it's the *wattage* conducted by the switch that counts.
These tactile switches everyone is using are rated at 12v, 50mA (or 0.6W). At the normal voltages (3.0-4.2v), we're pushing roughly 3-5 watts, so we're exceeding the rated capacity of the switch by a factor of 5-8. What does that mean?
It means the switch is going to have a much shorter service life than the normal several tens of thousands of activations it's rated for. Each time you hit the switch, the contacts corrode a little at the points of first and last contact, as that corrosion builds up, the switch eventually becomes intermittently functional, then non-functional.
It's not going to start on fire because if you are getting any significant amount of resistance, the contacts degrade *very* quickly (milliseconds), because they're a very thin film with no thermal tolerance. They're not going to short out, because there's not enough metal there to support a short for more than microseconds. They're just going to quit working.
Now, if we were significantly exceeding their maximum voltage, with some monster atomizer running off house current, an audio amp, or something, then Bad Things could happen. But at 3-8V, there just isn't enough electrical potential there to do anything but degrade the contacts. How long will that take? Could be anywhere from dozens to thousands of activations, since you're outside the rating profile there's no way to say, two switches from the same batch could be totally different.
Oh, and if the switch is rated for AC rather than DC, divide by 6.66 to get the ballpark equivalent DC for wattage purposes (I can't explain why without throwing out a bunch of vector trigonometry I barely remember and only half understood when I learned it).
So a 120VAC, 0.5A momentary switch like I currently have at my soldering station is equivalent to an 18V 0.5A, or 9W, and could carry over 2A at 4.2V, which is the target if you want a long-lived switch for an e-cig. Or you can use mosfet based solutions, which are more complicated electronically but then your only concern of the switch itself is actual failure from too much mechanical movement. Membrane PCB switches, for example, probably won't hack it, but the tiny switches they use in mouse buttons are perfect.
That pedometer switch.... I don't know, mechanically it should be fine but I doubt it's going to handle the current for long.
--Dave
