Waterproof switching.

Ok guys i want to brain storm.
The project is a dive light.
All complete except the switching mechanism.
needs to be water proof to 200m.
I can contain the switch inside the housing, but that makes switching on and off tricky. Thought of using FET.
The power will be about 14V, to run a HID lamp.
Any ideas?

Magnetic switch so there's no holes for water to get in. Also make only one opening, one place to seal the head to the tube so it minimizes any potential for o-ring bypass/ failure.

I deadset can't believe i didn't think of that thanks mate.
Do you know an online supplier?

yep, magnetic switches are the best for moisture immunity. For low power drain, use a reed switch. The reed switch can then be used to drive a mosfet or whatever. They are fairly rugged devices, considering how lightly built most are. They are used as the speed pick-up in most bicycle computers (i.e. speedometers). In this application, they open and close once for every rotation of the wheel. They also get smacked around a lot, and seem to survive quite well, so they are pretty rugged.

If you are feeling adventurous, see if you can figure out how to recharge the batteries without opening up the housing! This would allow you to permanently seal the housing. I've seen electric toothbrushes use a winding in the base as the secondary winding of a transformer. This is probably the most practical way to accomplish this goal, especially since you'll want to be transmitting a half watt or so. Capacitive coupling is an option, but it seems like you would either need huge plates, or very high frequencies, in order to transmit much power.

good luck,
Steve K.

Hi guyzz,

Here's my reed switch:



A little magnet is embedded in the green ring: Triggers two power relays to keep it on the safe side: HID can draw nasty startup-currents.

This is water resistant up to depths of 200 ft.

Ra.