Why not go all the way?

ringzero

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Jun 11, 2006
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LED lights are nearly there. Some of them already use a small switch merely to control the electronics. Why not go all the way to a solid state light? Eliminate that pesky mechanical switch completely for greater reliability.

How about two stainless steel or aluminum posts protruding outward through a molded plastic surround, which insulates them from each other and from the body of the light? (Or, maybe one post is grounded to the body.)

Touching both posts simultaneously with a finger tip completes a circuit which generates a pulse to the control electronics. (Maybe one post is hooked directly to the base of a Darlington pair.)

One touch on, second touch off. Or, the light is on whenever a fingertip bridges the posts, for momentary. Two rapid taps locks it on. A third tap turns it off. On a multilevel light, a series of taps controls brightness, strobe function, etc., just like a clicky switch. One obvious problem is that the light would switch on whenever water bridges the posts, but there may be ways to work around this.

Has anyone seen a light with a control like this?
 

paxxus

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May 29, 2006
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I have wondered about this too. I think maybe the operation of a SSS is unreliable with gloves on or in rainy weather. It should be pretty simple to make and it would probably be cheaper to manufacture and take up less space. If the light already has an uC (like HDS) it should be a total no-brainer, so there must be a reason why it's not used often (if ever).
 

gadgetnerd

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Interesting concept ringzero.

Another alternative would be to have capacitance sensing similar to that on iPods, Creative Zen Touch etc. I've no idea how much juice it would suck though. And come to think of it the touch interface on my Creative Zen Touch died for no reason, so there's robustness and reliability issues too!

I have to admit the idea of a completely solid state torch is pretty appealing.
 

PacketStorm

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Also take a look at the Gladius. Inherently it's a magnetically activated switch. Sure there's the mechanical pushbutton that moves the magnet into sensing range, but deep inside it's all solid state...
 

lukus

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Some of those little cheap bracelets that you get at fairs and carnivals that have the LEDs in them use a solid state switch like that. I've got a couple of them and they had what looked like little floppy plastic switches. One of the kids broke his "switch" and when I looked in it there was just 2 contacts from a circuit board underneath the switch. Moisten the tip of your finger and touch the contacts for off and on. Kinda cool for a toy.
 

ringzero

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Jun 11, 2006
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1,316
Thanks a lot to everyone who took time to reply.

A well designed and assembled solid state circuit with good conformal coating is orders of magnitude more reliable than any mechanical switch.

For added reliability - and much higher cost - the circuit can be 'burned in' after assembly. Put through its paces very rapidly, thousands of times a second, for several hours or even for several days. If it doesn't fail during burn in, it's highly unlikely to ever fail while in use.

When I get the time, I'll try the basic concept out on an old, plastic incandescent 2D I have laying around, which should have enough room in the head for the electronics. The basic momentary on - permanent on - off functions shouldn't require much more than a couple of transistors and a flip-flop. I'll drill through the plastic of the head and mount two small bolts to act as external contacts.

A better approach for small lights, 1AA or similar, would be a propoly or lexan body with a stainless ring set in the bezel, and a stainless ring set in the tailcap. The bezel and tailcap rings are the two contacts. (For longer lights, the tailcap contact ring could be set midway along the body of the light to preserve good ergonomics.)

Held naturally in the hand, the tailcap ring contacts the palm and small fingers, and extending the thumb or forefinger to touch the bezel ring completes the circuit. Should also work using a 'tactical' grip.

Operation of light would be independent of angular orientation in the hand, like with a tail clicky, unlike the case with a side-mounted clicky. Also, the contacts would be much less likely to shorted by rain or water droplets.

However, submerging the light, or dropping the light in mud, would turn it on. That could even be desirable in some circumstances. "That's not a bug - it's a feature!"

Jay R and greenLED:

Do either of you own the Indium?

Cool looking little light, but the website doesn't really explain much. Those two little metallic bumps near the center of the light - are those the touch contacts?


Packetstorm:

Yes, I've read about several lights with magnetic controls. Most of them have internal reed switches, which don't really count as solid state. They're a type of mechanical relay, although they're undoubtedly more reliable than mechanical switches. Some reed switches can reliably switch on and off thousands of times a second!

Seem to recall some light that uses a Hall Effect sensor, which does count as really solid state. That should be extremely reliable. So long as the external magnet is present, it should always work. For dive lights and such, an external movable magnet with an internal Hall Effect sensor is probably about the ultimate control system. But, due to the nature of magnets, this type of control system seems to require a very long switch throw to work reliably.
 
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